Fix what the review of this branch found, starting with the pick rule it only claimed

The off-screen rule for clicks was described in 3f0abf8 and in the pull request, but only its
comment was committed: pickAt still let the slop reach past the frame. The mutant that was said
to catch it matched nothing, and an unrelated flaky test failed instead. The frame test is now in
pickAt, before the slop, and its test fails without it (star at NDC 1.01, click at 0.995).

Venus, Uranus and Pluto turned forwards: Horizons states a retrograde spin twice, by a negative
rate and by an obliquity over 90 degrees, and both were applied. The period's sign is now used
only when no obliquity is known. Measured on the live markers, spin axis against orbit normal is
cos(obliquity) for each: Venus -0.999, Uranus -0.135, Pluto -0.494, Earth 0.917.

Moons listed as rates rather than "Synchronous" drifted about 5 degrees an orbit and Titan did not
turn: every moon is now locked at its Kepler period. Pluto's obliquity comes from IAU WGCCRE 2015,
Horizons gives none.

Also:
- the star's light is white at pi, not a warm 2.2 that left the photographs dim;
- procedural textures are 128x64, not 512x256 that froze the main thread ~60 ms a body;
- Io, Pluto, Titan and Deimos lose their "maps", which were disc photographs with black sky;
- an exoplanet with only a mass gets a radius from it (M^0.55, capped at Jupiter), not Earth's;
- the clock knows when it has left the present even once back at real time, so the date and
  "Back to now" stay up.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -37,14 +37,19 @@ jobs:
       # different dependency tree than the one committed.
       - run: npm ci
 
-      # Four TypeScript projects, checked by four different things. These two have no build of
+      # Five TypeScript projects, checked by four different things. These three have no build of
-      # their own, so nothing else would ever compile them.
+      # their own that checks them, so nothing else would ever compile them. The worker is bundled by
+      # the build, but esbuild only strips its types, and `tsconfig.app.json` leaves it out, since
+      # its lib is `webworker` rather than `dom`.
       - name: Typecheck the ETL
         run: npm run etl:typecheck
 
       - name: Typecheck the end-to-end tests
         run: npm run e2e:typecheck
 
+      - name: Typecheck the routing worker
+        run: npm run worker:typecheck
+
       # `tsconfig.spec.json` is compiled here, `tsconfig.app.json` by the build below.
       - name: Unit tests
         run: npm test -- --no-watch

.github/workflows/data-refresh.yml

@@ -39,9 +39,21 @@ jobs:
 
       - run: npm ci
 
-      # The ETL's cache directory is gitignored and this is a fresh runner, so every source is
+      # Gaia DR3 is a frozen release: the same query returns the same bytes (a live re-fetch has
-      # fetched live (~50-100 MB). A failed fetch fails the run by design — no refresh is
+      # reproduced stars.bin exactly), so its responses are carried from one run to the next
-      # better than a partial one — except Gaia, which the ETL itself treats as best-effort.
+      # rather than re-downloaded every week from an archive that times out under load. The key
+      # follows gaia.ts, where the queries are written, so a changed query is fetched afresh.
+      - uses: actions/cache@v4
+        with:
+          path: tools/etl/.cache/gaia-dr3-*.csv
+          key: gaia-dr3-${{ hashFiles('tools/etl/sources/gaia.ts') }}
+
+      # Every other source is fetched live on this fresh runner. A failed fetch fails the run by
+      # design — no refresh is better than a partial one. That includes Gaia on a cold cache, by
+      # two different paths: its Hipparcos cross-match is required, so an unreachable archive
+      # fails the run from fetchStars itself, while its main query is skipped when unreachable and
+      # the merge gate in build.ts then refuses a catalogue it contributed nothing to. An archive
+      # that answers short rather than not at all is caught in fetchGaiaStars.
       - name: Rebuild the datasets
         run: npm run etl
 

e2e/galaxy-view.spec.ts

@@ -40,4 +40,23 @@ test.describe('Galaxy view', () => {
     await page.getByRole('button', { name: 'Solar Neighbourhood' }).click();
     await expect(page.getByTestId('hud-title')).toHaveText('Local Stars', { timeout: 15_000 });
   });
+
+  test('a scale bar and labelled rings say how far things are, and follow the zoom', async ({ page }) => {
+    test.setTimeout(90_000);
+    await page.goto('/?stars=4000');
+    await expect(page.getByTestId('scene-canvas')).toBeVisible({ timeout: 30_000 });
+
+    // The rings are distances from the Sun, the survey's own edge called out among them.
+    await expect(page.getByText('Survey edge')).toBeVisible({ timeout: 30_000 });
+    const scale = page.getByTestId('hud-scale');
+    await expect(scale).toHaveAttribute('aria-label', /^Scale: [\d.]+ k?pc$/);
+    const opening = await scale.getAttribute('aria-label');
+
+    // Zooming in shortens the round length the bar stands for.
+    await page.getByTestId('scene-canvas').hover();
+    for (let notch = 0; notch < 10; notch++) {
+      await page.mouse.wheel(0, -400);
+    }
+    await expect(scale).not.toHaveAttribute('aria-label', opening ?? '', { timeout: 15_000 });
+  });
 });

package.json

@@ -10,7 +10,8 @@
     "etl": "tsx tools/etl/build.ts",
     "etl:typecheck": "tsc -p tools/etl/tsconfig.json --noEmit",
     "e2e": "playwright test",
-    "e2e:typecheck": "tsc -p e2e/tsconfig.json --noEmit"
+    "e2e:typecheck": "tsc -p e2e/tsconfig.json --noEmit",
+    "worker:typecheck": "tsc -p tsconfig.worker.json --noEmit"
   },
   "private": true,
   "packageManager": "npm@11.12.1",

src/app/features/galaxy-system/galaxy-system-scene.component.spec.ts

@@ -1,7 +1,7 @@
 import { ComponentFixture, TestBed } from '@angular/core/testing';
 import { Router } from '@angular/router';
 import * as THREE from 'three/webgpu';
-import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { afterEach, beforeEach, describe, expect, it, MockInstance, vi } from 'vitest';
 
 import { DataLoaderService, StarField } from '../../core/data/data-loader.service';
 import { EngineService, EngineTickCallback } from '../../core/engine/engine.service';
@@ -10,7 +10,13 @@ import { DeepSkyRecord } from '../../shared/models/deepsky.model';
 import { ExoplanetRecord } from '../../shared/models/exoplanet.model';
 import { StarRecord } from '../../shared/models/star.model';
 import { NavigationStore } from '../../shared/state/navigation.store';
+import { LinkBudget } from '../../shared/astro/jump-links';
+import { HudDisplay } from '../hud/hud-dock.component';
 import { GalaxySystemSceneComponent } from './galaxy-system-scene.component';
+import { galacticNormal } from './grid-plane';
+import { JumpLinkRenderer } from './jump-link-renderer';
+import { StarFieldRenderer } from './star-field-renderer';
+import { LabeledPoint, StarLabelOverlay } from './star-label-overlay';
 
 // jsdom does not implement ResizeObserver; the component only uses it to react to real
 // layout changes, which never happen in this headless test.
@@ -22,7 +28,8 @@ import { GalaxySystemSceneComponent } from './galaxy-system-scene.component';
 
 const SUN: StarRecord = { id: 0, name: 'Sol', x: 0, y: 0, z: 0, magnitude: -26.7, spectralType: 'G2V', colorIndex: 0.656 };
 const ALPHA_CENTAURI: StarRecord = { id: 1, name: 'Alpha Centauri', x: 1.34, y: 0, z: 0, magnitude: 4.4, spectralType: 'G2V', colorIndex: 0.7 };
-const PROXIMA: StarRecord = { id: 2, name: 'Proxima Centauri', x: 0, y: 1.3, z: 0, magnitude: 11.1, spectralType: 'M5V', colorIndex: 1.8 };
+// Its id deliberately differs from its place in STARS, so a lookup by id cannot pass for one by index.
+const PROXIMA: StarRecord = { id: 42, name: 'Proxima Centauri', x: 0, y: 1.3, z: 0, magnitude: 11.1, spectralType: 'M5V', colorIndex: 1.8 };
 
 const STARS: StarRecord[] = [SUN, ALPHA_CENTAURI, PROXIMA];
 const STAR_POSITIONS = new Float32Array(STARS.flatMap((star) => [star.x, star.y, star.z]));
@@ -94,14 +101,18 @@ class FakeEngineService {
 
   setProjection(projection: 'perspective' | 'orthographic', distanceToTarget: number): void {
     this.projection = projection;
+    this.orthographic.zoom = 1;
+    this.orthographic.position.copy(this.camera.position);
+    this.orthographic.quaternion.copy(this.camera.quaternion);
+    this.frameOrthographic(distanceToTarget);
+  }
+
+  frameOrthographic(distanceToTarget: number): void {
     const halfHeight = Math.max(distanceToTarget, 1e-6) * Math.tan((this.camera.fov * Math.PI) / 360);
     this.orthographic.top = halfHeight;
     this.orthographic.bottom = -halfHeight;
     this.orthographic.left = -halfHeight * this.camera.aspect;
     this.orthographic.right = halfHeight * this.camera.aspect;
-    this.orthographic.zoom = 1;
-    this.orthographic.position.copy(this.camera.position);
-    this.orthographic.quaternion.copy(this.camera.quaternion);
     this.orthographic.updateProjectionMatrix();
   }
 
@@ -124,6 +135,13 @@ class FakeEngineService {
 
   resize(): void {}
 
+  /** The canvas's device pixels per CSS pixel, as the renderer was told. */
+  pixelRatio = 1;
+
+  getRenderer(): { getPixelRatio(): number } {
+    return { getPixelRatio: () => this.pixelRatio };
+  }
+
   /** Test helper: simulates one rendered frame by invoking every registered tick callback. */
   tick(deltaSeconds: number): void {
     for (const callback of this.tickCallbacks) {
@@ -200,6 +218,602 @@ describe('GalaxySystemSceneComponent camera-flight transitions', () => {
     expect(navigationStore.viewLevel()).toBe('galaxy');
   });
 
+  it('clears a selection the catalogue no longer holds instead of chasing it', async () => {
+    // A bookmark saved against a Gaia row id that the next refresh renumbered. Before the guard,
+    // entering the missing system completed at once, completion re-read the same id, and the
+    // two recursed until the stack overflowed.
+    navigationStore.selectStar(987654321);
+    await flushAsync();
+
+    expect(navigationStore.selectedStarId()).toBeNull();
+    expect(navigationStore.viewLevel()).toBe('galaxy');
+  });
+
+  it('chooses the drawn stars again once the view centre has moved, and not for a small drift', async () => {
+    const component = fixture.componentInstance as unknown as { controls: { target: THREE.Vector3 } };
+    const refocus = vi.spyOn(StarFieldRenderer.prototype, 'refocus');
+    // The first pass always chooses; what is under test is the move after it.
+    await advanceFrames(engine, 0.3);
+    refocus.mockClear();
+
+    component.controls.target.set(40, 0, 0);
+    await advanceFrames(engine, 0.3);
+    expect(refocus).toHaveBeenCalledTimes(1);
+    expect(refocus.mock.calls[0][0].centre).toMatchObject({ x: 40, y: 0, z: 0 });
+
+    component.controls.target.set(42, 0, 0);
+    await advanceFrames(engine, 0.3);
+    expect(refocus).toHaveBeenCalledTimes(1);
+    refocus.mockRestore();
+  });
+
+  describe('the drawn stars, chosen for what the camera shows', () => {
+    type ViewScene = { controls: { target: THREE.Vector3; update(): void }; display: { update(change: (display: HudDisplay) => HudDisplay): void } };
+    let refocus: MockInstance<StarFieldRenderer['refocus']>;
+
+    beforeEach(() => {
+      refocus = vi.spyOn(StarFieldRenderer.prototype, 'refocus');
+    });
+    afterEach(() => refocus.mockRestore());
+
+    /** Swings the camera about the view's centre, around the scene's vertical, by `degrees`. */
+    function orbit(component: ViewScene, degrees: number): void {
+      const camera = engine.getCamera();
+      const target = component.controls.target;
+      camera.position.sub(target).applyAxisAngle(new THREE.Vector3(0, 1, 0), THREE.MathUtils.degToRad(degrees)).add(target);
+      component.controls.update();
+    }
+
+    it('chooses them for the opening view on the first pass, planet hosts included', async () => {
+      await advanceFrames(engine, 0.6);
+
+      expect(refocus).toHaveBeenCalledTimes(1);
+      const [focus] = refocus.mock.calls[0];
+      expect(focus.view).toBeDefined();
+      // The Sun has Earth, so it is a host; the others have nothing catalogued.
+      expect(Array.from(focus.hosts ?? [])).toEqual([1, 0, 0]);
+    });
+
+    it('chooses again once the camera has turned half the margin, and not for less', async () => {
+      const component = fixture.componentInstance as unknown as ViewScene;
+      await advanceFrames(engine, 0.3);
+
+      orbit(component, 1);
+      await advanceFrames(engine, 0.3);
+      expect(refocus).toHaveBeenCalledTimes(1);
+
+      orbit(component, 3);
+      await advanceFrames(engine, 0.3);
+      expect(refocus).toHaveBeenCalledTimes(2);
+    });
+
+    it('chooses again once a pan has moved the view further than a fifth of the neighbourhood, and not for less', async () => {
+      const component = fixture.componentInstance as unknown as ViewScene;
+      const camera = engine.getCamera();
+      // Camera and centre together, so the camera neither turns nor zooms.
+      const pan = (pc: number) => {
+        component.controls.target.x += pc;
+        camera.position.x += pc;
+        component.controls.update();
+      };
+      await advanceFrames(engine, 0.3);
+
+      pan(3);
+      await advanceFrames(engine, 0.3);
+      expect(refocus).toHaveBeenCalledTimes(1);
+
+      pan(3);
+      await advanceFrames(engine, 0.3);
+      expect(refocus).toHaveBeenCalledTimes(2);
+    });
+
+    it('chooses again once a zoom has changed the frame by half the margin, and not for less', async () => {
+      const component = fixture.componentInstance as unknown as ViewScene;
+      const camera = engine.getCamera();
+      const dolly = (factor: number) => camera.position.sub(component.controls.target).multiplyScalar(factor).add(component.controls.target);
+      await advanceFrames(engine, 0.3);
+
+      dolly(0.95);
+      await advanceFrames(engine, 0.3);
+      expect(refocus).toHaveBeenCalledTimes(1);
+
+      dolly(0.8);
+      await advanceFrames(engine, 0.3);
+      expect(refocus).toHaveBeenCalledTimes(2);
+    });
+
+    it('chooses again for the plan view, where a small turn moves deep stars furthest', async () => {
+      const component = fixture.componentInstance as unknown as ViewScene;
+      // About 10 pc of frame either side of the centre.
+      engine.getCamera().position.setLength(21.4);
+      component.controls.update();
+      await advanceFrames(engine, 0.3);
+      const beforePlan = refocus.mock.calls.length;
+
+      component.display.update((display) => ({ ...display, plan: true }));
+      TestBed.tick();
+      await advanceFrames(engine, 0.3);
+      expect(refocus).toHaveBeenCalledTimes(beforePlan + 1);
+
+      // Harmless under perspective; under the plan it moves a star 250 pc deep by 4 pc, against a 2.5 pc margin.
+      orbit(component, 1);
+      await advanceFrames(engine, 0.3);
+      expect(refocus).toHaveBeenCalledTimes(beforePlan + 2);
+    });
+
+    it('chooses again when the projection changes under a pose that has not moved at all', async () => {
+      await advanceFrames(engine, 0.3);
+      const before = refocus.mock.calls.length;
+      // The same place, direction and frame height, but a box instead of a frustum, which frames other stars.
+      const perspective = engine.getPerspectiveCamera();
+      const plan = (engine as unknown as { orthographic: THREE.OrthographicCamera }).orthographic;
+      plan.position.copy(perspective.position);
+      plan.quaternion.copy(perspective.quaternion);
+      engine.projection = 'orthographic';
+
+      await advanceFrames(engine, 0.3);
+
+      expect(refocus).toHaveBeenCalledTimes(before + 1);
+    });
+
+    it('holds a turn to the narrower side of a portrait frame', async () => {
+      const component = fixture.componentInstance as unknown as ViewScene;
+      engine.getPerspectiveCamera().aspect = 0.4;
+      engine.getPerspectiveCamera().updateProjectionMatrix();
+      await advanceFrames(engine, 0.3);
+
+      // Inside half the margin above and below, past half of it at the sides.
+      orbit(component, 2);
+      await advanceFrames(engine, 0.3);
+
+      expect(refocus).toHaveBeenCalledTimes(2);
+    });
+
+    it('keeps up with a flight frame by frame, from the frame it comes back into parsec space', async () => {
+      const component = fixture.componentInstance as unknown as ViewScene & { galaxyGroup: THREE.Group; rig: { isAnimating: boolean } };
+      navigationStore.selectStar(SUN.id);
+      await flushAsync();
+      await advanceFrames(engine, 2.5);
+      refocus.mockClear();
+
+      navigationStore.selectStar(null);
+      await flushAsync();
+      let choicesOnReturningFrame = -1;
+      let flightFrames = 0;
+      let flightChoices = 0;
+      for (let frame = 0; frame < 80; frame++) {
+        const wasInSystem = !component.galaxyGroup.visible;
+        const before = refocus.mock.calls.length;
+        engine.tick(0.05);
+        await flushAsync(1);
+        if (wasInSystem && component.galaxyGroup.visible) {
+          choicesOnReturningFrame = refocus.mock.calls.length - before;
+        }
+        if (component.galaxyGroup.visible && component.rig.isAnimating) {
+          flightFrames++;
+          flightChoices += refocus.mock.calls.length - before;
+        }
+      }
+
+      // Chosen for the view in the very frame the camera jumps back, not up to a pass later.
+      expect(choicesOnReturningFrame).toBe(1);
+      // The return zooms out from inside the system to the opening view: more re-choices than one a
+      // pass could make, and every one of them for the view.
+      expect(flightChoices).toBeGreaterThan(Math.ceil((flightFrames * 0.05) / 0.2));
+      expect(refocus.mock.calls.every(([focus]) => focus.view !== undefined)).toBe(true);
+    });
+
+    it('chooses once for the whole sky on the way out to the Galaxy, then leaves them alone', async () => {
+      const component = fixture.componentInstance as unknown as ViewScene;
+      engine.getCamera().position.set(0, 0, 30000);
+      await advanceFrames(engine, 0.3);
+      const onArrival = refocus.mock.calls.length;
+      expect(refocus.mock.calls.at(-1)![0].view).toBeUndefined();
+
+      component.controls.target.set(500, 0, 0);
+      await advanceFrames(engine, 0.3);
+      component.controls.target.set(1500, 0, 0);
+      await advanceFrames(engine, 0.3);
+
+      expect(refocus).toHaveBeenCalledTimes(onArrival);
+      expect(refocus.mock.calls.filter(([focus]) => focus.view === undefined)).toHaveLength(1);
+    });
+  });
+
+  describe('the local grid of distance rings', () => {
+    type GridScene = {
+      controls: { target: THREE.Vector3; update(): void };
+      display: { update(change: (display: HudDisplay) => HudDisplay): void };
+      localGridRadii: readonly number[];
+    };
+
+    it('sizes the rings by how far the frame reaches from the Sun, under either projection', async () => {
+      const component = fixture.componentInstance as unknown as GridScene;
+      const camera = engine.getCamera();
+      // Centred on a point 200 pc out along the galactic plane — where the rings are — seen from
+      // 20 pc above it. The rings have to reach it, and one of them has to cross the frame.
+      const normal = galacticNormal();
+      const centre = new THREE.Vector3(1, 0, 0).projectOnPlane(normal).normalize().multiplyScalar(200);
+      component.controls.target.copy(centre);
+      camera.position.copy(centre).addScaledVector(normal, 20);
+      component.controls.update();
+      await advanceFrames(engine, 0.3);
+      const underPerspective = [...component.localGridRadii];
+
+      component.display.update((display) => ({ ...display, plan: true }));
+      TestBed.tick();
+      await advanceFrames(engine, 0.3);
+
+      expect(underPerspective.at(-1)).toBeGreaterThanOrEqual(200);
+      // The frame is a band about 19 pc either side of 200 pc: rings out to 220 at a step sized to
+      // all 220 are 180 and 200, both of them off screen.
+      const halfHeight = engine.visibleHalfHeight(20);
+      expect(underPerspective.some((radius) => Math.abs(radius - 200) < halfHeight)).toBe(true);
+      // The plan view's wheel moves the frame rather than the camera, so "how far out the camera
+      // is" means something else there; what the rings have to cover does not.
+      expect([...component.localGridRadii]).toEqual(underPerspective);
+    });
+
+    it('measures the span in the plane the rings lie in, not through it', async () => {
+      const component = fixture.componentInstance as unknown as GridScene;
+      const camera = engine.getCamera();
+      // The same 200 pc out along the plane, but lifted 150 pc above it: 250 pc from the Sun as the
+      // crow flies, and still 200 pc out among the rings, which is the distance they are drawn at.
+      const normal = galacticNormal();
+      const centre = new THREE.Vector3(1, 0, 0).projectOnPlane(normal).normalize().multiplyScalar(200).addScaledVector(normal, 150);
+      component.controls.target.copy(centre);
+      camera.position.copy(centre).addScaledVector(normal, 20);
+      component.controls.update();
+      await advanceFrames(engine, 0.3);
+
+      const halfHeight = engine.visibleHalfHeight(20);
+      expect([...component.localGridRadii].some((radius) => Math.abs(radius - 200) < halfHeight)).toBe(true);
+    });
+
+    it('leaves the rings alone while the grid is not drawn', async () => {
+      const component = fixture.componentInstance as unknown as GridScene;
+      const camera = engine.getCamera();
+      await advanceFrames(engine, 0.3);
+      component.display.update((display) => ({ ...display, grid: false }));
+      TestBed.tick();
+      await advanceFrames(engine, 0.3);
+      const hidden = [...component.localGridRadii];
+
+      // A zoom this size crosses two round steps, and each crossing rebuilds every ring's vertices.
+      camera.position.setLength(camera.position.length() / 8);
+      component.controls.update();
+      await advanceFrames(engine, 0.3);
+
+      expect([...component.localGridRadii]).toEqual(hidden);
+    });
+
+    it('drops a ring label that a star name has taken, or that is off screen, and keeps the ladder otherwise', () => {
+      const component = fixture.componentInstance as unknown as {
+        ringLabelsInTheClear(candidates: readonly LabeledPoint[], camera: THREE.Camera, stars: readonly LabeledPoint[]): LabeledPoint[];
+      };
+      const camera = engine.getCamera();
+      camera.updateMatrixWorld(true);
+      const at = (x: number, y: number) => new THREE.Vector3(x, y, 0.5).unproject(camera);
+      // Rungs at a twentieth of the screen: well inside the separation two names would keep, and
+      // well outside the clearance a ring label keeps from a name, so neither test is a coin toss.
+      const near = at(0.1, 0.1);
+      const nextRungUp = at(0.1, 0.18);
+      const offScreen = at(1.6, 0.1);
+      const ladder: LabeledPoint[] = [
+        { id: 'ring-50', name: '50 pc', x: near.x, y: near.y, z: near.z },
+        { id: 'ring-100', name: '100 pc', x: nextRungUp.x, y: nextRungUp.y, z: nextRungUp.z },
+        { id: 'ring-150', name: '150 pc', x: offScreen.x, y: offScreen.y, z: offScreen.z }
+      ];
+
+      // A ladder of rings stays whole, though its rungs are closer than two star names would be.
+      expect(component.ringLabelsInTheClear(ladder, camera, []).map((label) => label.id)).toEqual(['ring-50', 'ring-100']);
+      // A star's name is worth more than a distance.
+      const star: LabeledPoint = { id: 7, name: 'Sirius', x: near.x, y: near.y, z: near.z };
+      expect(component.ringLabelsInTheClear(ladder, camera, [star]).map((label) => label.id)).toEqual(['ring-100']);
+    });
+
+    it('stays out of the text of a name, not just off its point', () => {
+      const component = fixture.componentInstance as unknown as {
+        ringLabelsInTheClear(candidates: readonly LabeledPoint[], camera: THREE.Camera, stars: readonly LabeledPoint[]): LabeledPoint[];
+        viewportAspect(): number;
+      };
+      const camera = engine.getCamera();
+      camera.updateMatrixWorld(true);
+      const aspect = component.viewportAspect();
+      const at = (x: number, y: number) => new THREE.Vector3(x / aspect, y, 0.5).unproject(camera);
+      // A hand's breadth apart on screen — past any clearance around the point — and on the same
+      // line, with the name's text running right through where the ring label starts.
+      const ring = at(0.125, -0.123);
+      const rung: LabeledPoint = { id: 'ring-50', name: '50 pc', x: ring.x, y: ring.y, z: ring.z };
+      const beside = at(0.06, -0.12);
+      const rightHand: LabeledPoint = { id: 7, name: 'Alpha Centauri', side: 'right', x: beside.x, y: beside.y, z: beside.z };
+
+      expect(component.ringLabelsInTheClear([rung], camera, [rightHand])).toEqual([]);
+      // The same name hanging the other way leaves that space empty, and the rung with it.
+      expect(component.ringLabelsInTheClear([rung], camera, [{ ...rightHand, side: 'left' }])).toEqual([rung]);
+
+      // And a rung to the left of a name keeps its place: "50 pc" is a third of a star name's
+      // width, so it ends well before the name starts, whatever the anchors' spacing suggests.
+      const centred = at(0, 0);
+      const spanning: LabeledPoint = { id: 8, name: 'Alnitak', side: 'right', x: centred.x, y: centred.y, z: centred.z };
+      const toTheLeft = at(-0.25, 0.02);
+      const clearRung: LabeledPoint = { id: 'ring-100', name: '100 pc', x: toTheLeft.x, y: toTheLeft.y, z: toTheLeft.z };
+
+      expect(component.ringLabelsInTheClear([clearRung], camera, [spanning])).toEqual([clearRung]);
+    });
+
+    it('places the ring labels with the star names rather than over them', async () => {
+      const component = fixture.componentInstance as unknown as GridScene;
+      const update = vi.spyOn(StarLabelOverlay.prototype, 'update');
+      const cleared = vi.spyOn(GalaxySystemSceneComponent.prototype as unknown as { ringLabelsInTheClear: (...args: unknown[]) => LabeledPoint[] }, 'ringLabelsInTheClear');
+      const camera = engine.getCamera();
+      camera.position.set(0, 4, 10);
+      component.controls.target.set(0, 0, 0);
+      component.controls.update();
+      await advanceFrames(engine, 0.3);
+
+      const labels = (update.mock.calls.at(-1)?.[0] ?? []) as LabeledPoint[];
+      const rings = labels.filter((label) => String(label.id).startsWith('ring-'));
+      expect(rings.length).toBeGreaterThan(0);
+      // Handed over as the clearing pass left them, not as the grid produced them.
+      expect(cleared).toHaveBeenCalled();
+      expect(rings).toEqual(cleared.mock.results.at(-1)?.value);
+      update.mockRestore();
+      cleared.mockRestore();
+    });
+  });
+
+  it('keeps the stars of a plotted route drawn, and the selected star', async () => {
+    const component = fixture.componentInstance as unknown as { routeResult: { set(value: unknown): void } };
+    const refocus = vi.spyOn(StarFieldRenderer.prototype, 'refocus');
+    await advanceFrames(engine, 0.3);
+
+    component.routeResult.set({ stars: [{ id: SUN.id, name: 'Sol' }, { id: PROXIMA.id, name: 'Proxima Centauri' }], totalPc: 1.3, neededRangePc: null, gaveUp: false, least: true });
+    await advanceFrames(engine, 0.3);
+
+    // As catalogue indices: the Sun is the first entry of STARS, Proxima the third.
+    expect(refocus.mock.calls.at(-1)![0].pinned).toEqual([0, 2]);
+    refocus.mockRestore();
+  });
+
+  describe('the jump-link graph', () => {
+    type LinkScene = {
+      routing: { links(rangePc: number, drawn: Uint32Array, budget?: LinkBudget): Promise<Float32Array>; route(): Promise<never>; dispose(): void };
+      display: { update(change: (display: { jumpLinks: boolean }) => unknown): void };
+      jumpRangePc: { set(rangePc: number): void };
+      routeResult: { set(value: unknown): void };
+      controls: { target: THREE.Vector3 };
+      starField: { drawnStars: Uint32Array; drawn: Uint32Array };
+    };
+    /** Real time, since the rebuild waits on a real timer for the range and the drawn stars to settle. */
+    const settle = () => new Promise((resolve) => setTimeout(resolve, 300));
+
+    function linkScene(links: LinkScene['routing']['links']): LinkScene {
+      const component = fixture.componentInstance as unknown as LinkScene;
+      component.routing = { links, route: () => new Promise<never>(() => undefined), dispose: () => undefined };
+      component.display.update((display) => ({ ...display, jumpLinks: true }));
+      TestBed.tick();
+      return component;
+    }
+
+    /** Makes the next refocus choose a different set: the field is told it draws one star, then the view moves. */
+    async function changeDrawnStars(component: LinkScene, targetX: number): Promise<void> {
+      component.starField.drawn = Uint32Array.of(0);
+      component.controls.target.set(targetX, 0, 0);
+      await advanceFrames(engine, 0.3);
+    }
+
+    it('links the stars being drawn, and asks again once a new set of them holds still', async () => {
+      const links = vi.fn((_rangePc: number, _drawn: Uint32Array) => Promise.resolve(new Float32Array(0)));
+      const component = linkScene(links);
+      await settle();
+      expect(links).toHaveBeenCalledTimes(1);
+      expect(links.mock.calls[0].slice(0, 2)).toEqual([3, component.starField.drawnStars]);
+
+      await changeDrawnStars(component, 40);
+      expect(links).toHaveBeenCalledTimes(1);
+      await settle();
+      expect(links).toHaveBeenCalledTimes(2);
+      expect(links.mock.calls[1][1]).toBe(component.starField.drawnStars);
+      expect(links.mock.calls[1][1]).not.toBe(links.mock.calls[0][1]);
+
+      // A route re-chooses the drawn stars around its pins, and here they come out the same: no new graph.
+      component.routeResult.set({ stars: [{ id: SUN.id, name: 'Sol' }], totalPc: 0, neededRangePc: null, gaveUp: false, least: true });
+      await advanceFrames(engine, 0.3);
+      await settle();
+      expect(links).toHaveBeenCalledTimes(2);
+    });
+
+    it('asks for as much of the graph as a million pixels of line make, around where the view is centred', async () => {
+      const links = vi.fn((_rangePc: number, _drawn: Uint32Array, _budget?: LinkBudget) => Promise.resolve(new Float32Array(0)));
+      Object.defineProperty((fixture.nativeElement as HTMLElement).querySelector('canvas')!, 'clientHeight', { value: 1080 });
+      // A screen scaled to 200%: 1080 CSS pixels are 2160 drawn ones, and the lines are drawn in those.
+      engine.pixelRatio = 2;
+      linkScene(links);
+      await settle();
+
+      const budget = links.mock.calls[0][2];
+      // The view opens centred on the Sun: its frame's half-height there, over 1080 drawn pixels, is a pixel's worth of parsecs.
+      const halfHeight = engine.getCamera().position.length() * Math.tan((50 * Math.PI) / 360);
+      expect(budget?.centre).toEqual({ x: 0, y: 0, z: 0 });
+      expect(budget?.lengthPc).toBeCloseTo((1_000_000 * halfHeight) / 1080, 3);
+    });
+
+    it('asks again once the view has zoomed past the budget it asked with, though the drawn stars are the same', async () => {
+      // All three stars fit the star budget, so the drawn set never changes: only the budget can.
+      const links = vi.fn((_rangePc: number, _drawn: Uint32Array, _budget?: LinkBudget) => Promise.resolve(new Float32Array(0)));
+      Object.defineProperty((fixture.nativeElement as HTMLElement).querySelector('canvas')!, 'clientHeight', { value: 1080 });
+      const component = linkScene(links);
+      await advanceFrames(engine, 0.3);
+      await settle();
+      const asked = links.mock.calls.length;
+
+      const camera = engine.getCamera();
+      camera.position.sub(component.controls.target).multiplyScalar(0.5).add(component.controls.target);
+      await advanceFrames(engine, 0.3);
+      await settle();
+
+      expect(links.mock.calls.length).toBe(asked + 1);
+      expect(links.mock.calls.at(-1)![1]).toBe(links.mock.calls[0][1]);
+    });
+
+    it('asks for no graph from inside a system, where distances are in astronomical units', async () => {
+      const links = vi.fn((_rangePc: number, _drawn: Uint32Array, _budget?: LinkBudget) => Promise.resolve(new Float32Array(0)));
+      navigationStore.selectStar(SUN.id);
+      await flushAsync();
+      await advanceFrames(engine, 2.5);
+
+      linkScene(links);
+      await settle();
+
+      expect(links).not.toHaveBeenCalled();
+    });
+
+    it('keeps what it asked for when an older request it replaced is rejected', async () => {
+      // Off and on again while a graph is still waiting: the waiting one is replaced, and its
+      // rejection must not be taken for the request that replaced it.
+      const pending: Array<{ resolve: (segments: Float32Array) => void; reject: (error: Error) => void }> = [];
+      const setSegments = vi.spyOn(JumpLinkRenderer.prototype, 'setSegments');
+      const component = linkScene(() => new Promise<Float32Array>((resolve, reject) => pending.push({ resolve, reject })));
+      await settle();
+      component.display.update((display) => ({ ...display, jumpLinks: false }));
+      TestBed.tick();
+      await settle();
+      component.display.update((display) => ({ ...display, jumpLinks: true }));
+      TestBed.tick();
+      await settle();
+      expect(pending).toHaveLength(2);
+
+      pending[0].reject(new Error('Superseded by a newer request'));
+      await flushAsync();
+      const graph = new Float32Array(6);
+      pending[1].resolve(graph);
+      await flushAsync();
+
+      expect(setSegments).toHaveBeenLastCalledWith(graph);
+      setSegments.mockRestore();
+    });
+
+    it('gives a view on the move a new graph at least every quarter second, rather than waiting for it to stop', async () => {
+      const links = vi.fn((_rangePc: number, _drawn: Uint32Array) => Promise.resolve(new Float32Array(0)));
+      const component = linkScene(links);
+      await settle();
+
+      // A new drawn set about every 150 ms for a second, as an orbit makes one each pass.
+      for (let pass = 1; pass <= 7; pass++) {
+        await changeDrawnStars(component, pass * 40);
+        await new Promise((resolve) => setTimeout(resolve, 120));
+      }
+
+      expect(links.mock.calls.length).toBeGreaterThanOrEqual(3);
+    });
+
+    it('draws a late graph for the range still asked for, and not one for a range left behind', async () => {
+      const answers: Array<(segments: Float32Array) => void> = [];
+      const setSegments = vi.spyOn(JumpLinkRenderer.prototype, 'setSegments');
+      const component = linkScene(() => new Promise<Float32Array>((resolve) => answers.push(resolve)));
+      await settle();
+      await changeDrawnStars(component, 40);
+      await settle();
+      expect(answers).toHaveLength(2);
+
+      // For stars no longer drawn, but at the range still asked for: newer than what is on screen.
+      const olderSet = new Float32Array(6);
+      answers[0](olderSet);
+      await flushAsync();
+      expect(setSegments).toHaveBeenLastCalledWith(olderSet);
+
+      component.jumpRangePc.set(5);
+      TestBed.tick();
+      await settle();
+      expect(answers).toHaveLength(3);
+      answers[1](new Float32Array(12));
+      await flushAsync();
+      expect(setSegments).toHaveBeenLastCalledWith(olderSet);
+
+      const current = new Float32Array(18);
+      answers[2](current);
+      await flushAsync();
+      expect(setSegments).toHaveBeenLastCalledWith(current);
+      setSegments.mockRestore();
+    });
+  });
+
+  it('shows the answer to the latest route asked for, whatever order the answers arrive in', async () => {
+    type Answer = { route: { stars: number[]; totalPc: number; longestHopPc: number } | null; neededRangePc: number | null; gaveUp: boolean; least: boolean };
+    const answers: Array<(answer: Answer) => void> = [];
+    const component = fixture.componentInstance as unknown as {
+      routing: { route(): Promise<Answer>; links(): Promise<Float32Array>; dispose(): void };
+      routePending(): boolean;
+      routeResult(): { stars: { id: number }[]; gaveUp: boolean } | null;
+      onRouteRequested(request: { fromId: number; toId: number; rangePc: number }): void;
+    };
+    component.routing = {
+      route: () => new Promise<Answer>((resolve) => answers.push(resolve)),
+      links: () => Promise.resolve(new Float32Array(0)),
+      dispose: () => undefined
+    };
+
+    component.onRouteRequested({ fromId: SUN.id, toId: ALPHA_CENTAURI.id, rangePc: 2 });
+    component.onRouteRequested({ fromId: SUN.id, toId: PROXIMA.id, rangePc: 2 });
+    expect(component.routePending()).toBe(true);
+
+    answers[1]({ route: { stars: [SUN.id, PROXIMA.id], totalPc: 1.3, longestHopPc: 1.3 }, neededRangePc: null, gaveUp: false, least: true });
+    await flushAsync();
+    answers[0]({ route: { stars: [SUN.id, ALPHA_CENTAURI.id], totalPc: 1.34, longestHopPc: 1.34 }, neededRangePc: null, gaveUp: false, least: true });
+    await flushAsync();
+
+    expect(component.routeResult()?.stars.map((star) => star.id)).toEqual([SUN.id, PROXIMA.id]);
+    expect(component.routePending()).toBe(false);
+
+    // "It gave up" travels to the panel, which says something else for it than for "there is none".
+    component.onRouteRequested({ fromId: SUN.id, toId: ALPHA_CENTAURI.id, rangePc: 0.5 });
+    answers[2]({ route: null, neededRangePc: null, gaveUp: true, least: false });
+    await flushAsync();
+    expect(component.routeResult()).toMatchObject({ stars: [], gaveUp: true });
+  });
+
+  it('releases the routes panel when a route cannot be worked out, so it can be tried again', async () => {
+    const component = fixture.componentInstance as unknown as {
+      routing: { route(): Promise<never>; links(): Promise<Float32Array>; dispose(): void };
+      routePending(): boolean;
+      onRouteRequested(request: { fromId: number; toId: number; rangePc: number }): void;
+    };
+    const logged = vi.spyOn(console, 'error').mockImplementation(() => undefined);
+    component.routing = { route: () => Promise.reject(new Error('worker gone')), links: () => Promise.resolve(new Float32Array(0)), dispose: () => undefined };
+
+    component.onRouteRequested({ fromId: SUN.id, toId: PROXIMA.id, rangePc: 2 });
+    await flushAsync();
+
+    expect(component.routePending()).toBe(false);
+    expect(logged).toHaveBeenCalled();
+    logged.mockRestore();
+  });
+
+  it('asks for no more label candidates once the last label it will show is placed', () => {
+    // Near the Sun a label candidate past the fifteenth can sit at the far end of the catalogue's
+    // brightness order, so asking for one more than is used can cost a walk of the whole order.
+    const component = fixture.componentInstance as unknown as {
+      spreadLabels(candidates: Iterable<{ id: number; name: string; x: number; y: number; z: number }>, camera: THREE.Camera, keepId: null): unknown[];
+    };
+    const camera = engine.getCamera();
+    camera.updateMatrixWorld(true);
+    camera.updateProjectionMatrix();
+    let pulled = 0;
+    const grid = function* () {
+      for (let row = 0; row < 5; row++) {
+        for (let column = 0; column < 5; column++) {
+          pulled++;
+          const point = new THREE.Vector3(-0.8 + column * 0.4, -0.8 + row * 0.4, 0.5).unproject(camera);
+          yield { id: row * 5 + column, name: `label-${pulled}`, x: point.x, y: point.y, z: point.z };
+        }
+      }
+    };
+
+    expect(component.spreadLabels(grid(), camera, null)).toHaveLength(15);
+    expect(pulled).toBe(15);
+  });
+
   it('flies the camera into a selected star system: hides the galaxy group, shows the system group, and switches to AU-scale near/far planes', async () => {
     navigationStore.selectStar(SUN.id);
     await flushAsync();

src/app/features/galaxy-system/jump-link-renderer.ts

@@ -1,7 +1,5 @@
 import * as THREE from 'three/webgpu';
 
-import { JumpLink } from '../../shared/astro/jump-links';
-
 /** Faint, because there are tens of thousands of them and none is worth reading on its own. */
 const LINK_OPACITY = 0.16;
 /** The one route is the figure; the graph it is drawn on is the ground. */
@@ -48,23 +46,17 @@ export class JumpLinkRenderer {
     this.links.frustumCulled = false;
     this.route.frustumCulled = false;
     this.object.add(this.links, this.route);
-    this.setLinks([], () => undefined);
+    this.setSegments(new Float32Array(0));
     this.setRoute([], () => undefined);
   }
 
-  setLinks(links: readonly JumpLink[], positionOf: (starId: number) => LinkPoint | undefined): void {
+  /** The graph, as vertex pairs: six floats a link, one end then the other. See `jumpLinkSegments`. */
-    const vertices = new Float32Array(links.length * 6);
+  setSegments(vertices: Float32Array): void {
-    let at = 0;
+    this.replaceGeometry(this.links, vertices);
-    for (const link of links) {
+    // Given rather than left for the renderer to compute: it wants a bounding sphere to sort by and,
-      const from = positionOf(link.from);
+    // finding none, walks every vertex on the main thread in the first frame that draws the graph.
-      const to = positionOf(link.to);
+    // The graph is never culled, and it sorts by its centre, where the catalogue is centred too.
-      if (!from || !to) {
+    this.links.geometry.boundingSphere = new THREE.Sphere(new THREE.Vector3(), Infinity);
-        continue;
-      }
-      vertices.set([from.x, from.y, from.z, to.x, to.y, to.z], at);
-      at += 6;
-    }
-    this.replaceGeometry(this.links, at === vertices.length ? vertices : vertices.subarray(0, at));
   }
 
   /** The chain to draw over the graph, departure first. Fewer than two stars draws nothing. */

src/app/features/galaxy-system/routing-client.spec.ts

@@ -0,0 +1,259 @@
+import { describe, expect, it } from 'vitest';
+
+import { jumpLinkSegments, routeBetween } from '../../shared/astro/jump-links';
+import { RoutingRequest, RoutingResponse } from '../../shared/astro/routing';
+import { StarNeighbourhood } from '../../shared/astro/star-neighbourhood';
+import { StarRecord } from '../../shared/models/star.model';
+import { RoutingClient, SupersededRequest } from './routing-client';
+
+const STARS: StarRecord[] = Array.from({ length: 6 }, (_, i) => ({
+  id: 100 + i,
+  name: `star-${i}`,
+  x: i < 5 ? i : 9,
+  y: 0,
+  z: 0,
+  magnitude: 5,
+  spectralType: 'G2V',
+  colorIndex: 0.6
+}));
+const POSITIONS = Float32Array.from(STARS.flatMap((star) => [star.x, star.y, star.z]));
+const index = new StarNeighbourhood(STARS);
+/** Every star drawn. */
+const ALL = Uint32Array.from(STARS.keys());
+
+/** Flushes settled promises and their handlers. */
+const flush = () => new Promise((resolve) => setTimeout(resolve, 0));
+
+/** A worker that records what it is sent and answers only when told to. */
+class FakeWorker {
+  readonly sent: Array<RoutingRequest | { kind: 'catalogue' }> = [];
+  readonly transferred: ArrayBufferLike[] = [];
+  private readonly listeners: Record<string, Array<(event: { data?: unknown }) => void>> = {};
+  terminated = false;
+
+  postMessage(message: RoutingRequest | { kind: 'catalogue' }, transfer: Transferable[] = []): void {
+    this.sent.push(message);
+    this.transferred.push(...(transfer as ArrayBufferLike[]));
+  }
+
+  addEventListener(type: string, listener: (event: { data?: unknown }) => void): void {
+    (this.listeners[type] ??= []).push(listener);
+  }
+
+  terminate(): void {
+    this.terminated = true;
+  }
+
+  /** The requests sent so far, catalogue aside. */
+  get requests(): RoutingRequest[] {
+    return this.sent.filter((message): message is RoutingRequest => message.kind !== 'catalogue');
+  }
+
+  answer(response: RoutingResponse): void {
+    for (const listener of this.listeners['message'] ?? []) listener({ data: response });
+  }
+
+  fail(): void {
+    for (const listener of this.listeners['error'] ?? []) listener({});
+  }
+}
+
+function clientWithFake(): { client: RoutingClient; worker: FakeWorker } {
+  const worker = new FakeWorker();
+  const client = new RoutingClient(STARS, POSITIONS, index, () => worker as unknown as Worker);
+  return { client, worker };
+}
+
+// The unit tests' DOM has no Worker, which is exactly the case the client answers in place.
+describe('RoutingClient without a worker', () => {
+  it('has no Worker to use here, so the in-place answers are what is being tested', () => {
+    expect(typeof Worker).toBe('undefined');
+  });
+
+  it('answers a route from the index it was given', async () => {
+    const client = new RoutingClient(STARS, POSITIONS, index);
+
+    await expect(client.route(100, 104, 1.5, 8)).resolves.toEqual({ route: routeBetween(index, 100, 104, 1.5).route, neededRangePc: null, gaveUp: false, least: true });
+    client.dispose();
+  });
+
+  it('answers a refused route with the range that would open it', async () => {
+    const client = new RoutingClient(STARS, POSITIONS, index);
+
+    const answer = await client.route(100, 105, 1.5, 8);
+
+    expect(answer.route).toBeNull();
+    expect(answer.neededRangePc).toBeCloseTo(5, 1);
+    client.dispose();
+  });
+
+  it('answers the graph as segments', async () => {
+    const client = new RoutingClient(STARS, POSITIONS, index);
+
+    expect(Array.from(await client.links(1.5, ALL))).toEqual(Array.from(jumpLinkSegments(index, 1.5)));
+    client.dispose();
+  });
+
+  it('keeps only the links its budget holds, nearest the centre first', async () => {
+    const client = new RoutingClient(STARS, POSITIONS, index);
+
+    // Stars at x = 0 to 4 a parsec apart: from a centre at 3.9, one and a half parsecs is the link 3-4 alone.
+    const segments = await client.links(1.5, ALL, { centre: { x: 3.9, y: 0, z: 0 }, lengthPc: 1.5 });
+
+    expect(Array.from(segments)).toEqual([3, 0, 0, 4, 0, 0]);
+    client.dispose();
+  });
+
+  it('links only the stars it is told are drawn', async () => {
+    const client = new RoutingClient(STARS, POSITIONS, index);
+
+    // Stars at x = 0, 1 and 3: only the first two are within 1.5 pc of each other.
+    expect(Array.from(await client.links(1.5, Uint32Array.of(0, 1, 3)))).toEqual([0, 0, 0, 1, 0, 0]);
+    client.dispose();
+  });
+});
+
+describe('RoutingClient with a worker', () => {
+  it('sends the catalogue first, then one request at a time', () => {
+    const { client, worker } = clientWithFake();
+
+    void client.links(8, ALL);
+    void client.links(3, ALL);
+
+    expect(worker.sent[0].kind).toBe('catalogue');
+    expect(worker.requests).toHaveLength(1);
+    client.dispose();
+  });
+
+  // A graph at 8 pc is seconds of work the worker cannot drop once started. Every pause on the
+  // range slider used to queue another, and a route asked for after them waited behind them all.
+  it('replaces a waiting graph with the newer one before it is ever built, and sends a route ahead of it', async () => {
+    const { client, worker } = clientWithFake();
+    const first = client.links(5, ALL);
+    const superseded = client.links(6, ALL).catch((error: unknown) => error);
+    const latest = client.links(8, ALL);
+    const route = client.route(100, 104, 1.5, 8);
+
+    const building = worker.requests[0];
+    worker.answer({ kind: 'links', requestId: building.requestId, segments: new Float32Array(6) });
+    await flush();
+
+    expect(await superseded).toBeInstanceOf(SupersededRequest);
+    expect(worker.requests.map((request) => request.kind)).toEqual(['links', 'route']);
+    await expect(first).resolves.toHaveLength(6);
+
+    const routeRequest = worker.requests[1];
+    worker.answer({ kind: 'route', requestId: routeRequest.requestId, route: null, neededRangePc: 4, gaveUp: false, least: true });
+    await expect(route).resolves.toEqual({ route: null, neededRangePc: 4, gaveUp: false, least: true });
+    await flush();
+
+    expect(worker.requests.map((request) => (request.kind === 'links' ? request.rangePc : request.kind))).toEqual([5, 'route', 8]);
+    const lastGraph = worker.requests[2];
+    worker.answer({ kind: 'links', requestId: lastGraph.requestId, segments: new Float32Array(12) });
+    await expect(latest).resolves.toHaveLength(12);
+    client.dispose();
+  });
+
+  it('shares the answer to a route already on its way rather than asking it twice', async () => {
+    const { client, worker } = clientWithFake();
+    const once = client.route(100, 104, 1.5, 8);
+    const again = client.route(100, 104, 1.5, 8);
+    const widerRange = client.route(100, 104, 2.5, 8);
+
+    expect(worker.requests).toHaveLength(1);
+    worker.answer({ kind: 'route', requestId: worker.requests[0].requestId, route: null, neededRangePc: 4, gaveUp: false, least: true });
+
+    expect(await again).toEqual(await once);
+    await flush();
+    // The same two stars at another range is another question.
+    expect(worker.requests.map((request) => request.rangePc)).toEqual([1.5, 2.5]);
+    worker.answer({ kind: 'route', requestId: worker.requests[1].requestId, route: null, neededRangePc: null, gaveUp: false, least: true });
+    await expect(widerRange).resolves.toEqual({ route: null, neededRangePc: null, gaveUp: false, least: true });
+    client.dispose();
+  });
+
+  // Turning the layer off and on again while the worker is busy asks for the same graph twice. Were
+  // the second to replace the first, the first's rejection would wipe the scene's record of the second.
+  it('shares a graph already on its way for the same range and the same list of drawn stars', async () => {
+    const { client, worker } = clientWithFake();
+    const drawn = Uint32Array.of(0, 1, 2);
+    const building = client.links(3, drawn);
+    const waiting = client.links(5, drawn);
+    const again = client.links(5, drawn);
+    const sameAsBuilding = client.links(3, drawn);
+
+    worker.answer({ kind: 'links', requestId: worker.requests[0].requestId, segments: new Float32Array(6) });
+    await expect(building).resolves.toHaveLength(6);
+    await expect(sameAsBuilding).resolves.toHaveLength(6);
+    await flush();
+    worker.answer({ kind: 'links', requestId: worker.requests[1].requestId, segments: new Float32Array(12) });
+    await expect(waiting).resolves.toHaveLength(12);
+    await expect(again).resolves.toHaveLength(12);
+    expect(worker.requests.map((request) => request.kind === 'links' && request.rangePc)).toEqual([3, 5]);
+    client.dispose();
+  });
+
+  it('builds a graph for each set of drawn stars asked about, and never gives the list away', async () => {
+    const { client, worker } = clientWithFake();
+    const near = Uint32Array.of(0, 1, 2);
+    const far = Uint32Array.of(3, 4, 5);
+    void client.links(3, near);
+    const second = client.links(3, far);
+
+    worker.answer({ kind: 'links', requestId: worker.requests[0].requestId, segments: new Float32Array(6) });
+    await flush();
+
+    expect(worker.requests.map((request) => request.kind === 'links' && Array.from(request.drawn))).toEqual([[0, 1, 2], [3, 4, 5]]);
+    worker.answer({ kind: 'links', requestId: worker.requests[1].requestId, segments: new Float32Array(12) });
+    await expect(second).resolves.toHaveLength(12);
+    // The same list at a different budget is a different graph.
+    void client.links(3, far, { centre: { x: 1, y: 0, z: 0 }, lengthPc: 10 });
+    void client.links(3, far, { centre: { x: 1, y: 0, z: 0 }, lengthPc: 20 });
+    worker.answer({ kind: 'links', requestId: worker.requests[2].requestId, segments: new Float32Array(0) });
+    await flush();
+    expect(worker.requests.map((request) => request.kind === 'links' && request.budget?.lengthPc)).toEqual([undefined, undefined, 10, 20]);
+    // The star field goes on drawing and picking from these lists, so they are copied, not moved.
+    expect(worker.transferred).not.toContain(near.buffer);
+    expect(worker.transferred).not.toContain(far.buffer);
+    client.dispose();
+  });
+
+  it('hands on that the search gave up, along with the answer it did give', async () => {
+    const { client, worker } = clientWithFake();
+    const answer = client.route(100, 105, 1.5, 8);
+
+    worker.answer({ kind: 'route', requestId: worker.requests[0].requestId, route: null, neededRangePc: null, gaveUp: true, least: false });
+
+    await expect(answer).resolves.toEqual({ route: null, neededRangePc: null, gaveUp: true, least: false });
+    client.dispose();
+  });
+
+  it('rejects a request the worker failed on, and goes on to the next', async () => {
+    const { client, worker } = clientWithFake();
+    const failing = client.route(100, 104, 1.5, 8).catch((error: unknown) => error);
+    const next = client.links(3, ALL);
+
+    worker.answer({ kind: 'failed', requestId: worker.requests[0].requestId, message: 'out of memory' });
+
+    expect(((await failing) as Error).message).toBe('out of memory');
+    await flush();
+    expect(worker.requests.map((request) => request.kind)).toEqual(['route', 'links']);
+    worker.answer({ kind: 'links', requestId: worker.requests[1].requestId, segments: new Float32Array(0) });
+    await expect(next).resolves.toHaveLength(0);
+    client.dispose();
+  });
+
+  it('answers in place what a worker that failed to load left outstanding, and everything after', async () => {
+    const { client, worker } = clientWithFake();
+    const route = client.route(100, 104, 1.5, 8);
+    const graph = client.links(1.5, Uint32Array.of(0, 1, 3));
+
+    worker.fail();
+
+    await expect(route).resolves.toEqual({ route: routeBetween(index, 100, 104, 1.5).route, neededRangePc: null, gaveUp: false, least: true });
+    expect(Array.from(await graph)).toEqual([0, 0, 0, 1, 0, 0]);
+    await expect(client.route(100, 105, 1.5, 8)).resolves.toMatchObject({ route: null });
+    expect(worker.terminated).toBe(true);
+    client.dispose();
+  });
+});

src/app/features/galaxy-system/routing-client.ts

@@ -0,0 +1,199 @@
+import { answerRouting, RoutingRequest, RoutingResponse } from '../../shared/astro/routing';
+import { LinkBudget, Route } from '../../shared/astro/jump-links';
+import { StarNeighbourhood } from '../../shared/astro/star-neighbourhood';
+import { StarRecord } from '../../shared/models/star.model';
+
+export interface RouteAnswer {
+  readonly route: Route | null;
+  readonly neededRangePc: number | null;
+  /** True when the search at the range asked for gave up rather than ruling a route out. */
+  readonly gaveUp: boolean;
+  /** True when the search for a range that would work looked everywhere up to the ceiling. */
+  readonly least: boolean;
+}
+
+/** A request dropped before it was sent, because a newer one of the same kind replaced it. */
+export class SupersededRequest extends Error {
+  constructor() {
+    super('Superseded by a newer request');
+  }
+}
+
+/** A request made and not yet answered: what was asked, and the promise whoever asked is holding. */
+interface Outstanding {
+  readonly request: RoutingRequest;
+  readonly promise: Promise<RoutingResponse>;
+  readonly resolve: (response: RoutingResponse) => void;
+  readonly reject: (error: Error) => void;
+}
+
+function outstanding(request: RoutingRequest): Outstanding {
+  let resolve!: (response: RoutingResponse) => void;
+  let reject!: (error: Error) => void;
+  const promise = new Promise<RoutingResponse>((onResolve, onReject) => {
+    resolve = onResolve;
+    reject = onReject;
+  });
+  return { request, promise, resolve, reject };
+}
+
+/**
+ * Whether two requests ask the same question. A graph is the same when it is for the same range, the
+ * same budget and the very same list of drawn stars: the star field replaces that list whenever the
+ * set changes, so one array is one set, and comparing 70 000 indices would cost more than sharing
+ * could save.
+ */
+function asksTheSame(a: RoutingRequest, b: RoutingRequest): boolean {
+  if (a.kind === 'links' || b.kind === 'links') {
+    return (
+      a.kind === 'links' &&
+      b.kind === 'links' &&
+      a.rangePc === b.rangePc &&
+      a.drawn === b.drawn &&
+      a.budget?.lengthPc === b.budget?.lengthPc &&
+      a.budget?.centre.x === b.budget?.centre.x &&
+      a.budget?.centre.y === b.budget?.centre.y &&
+      a.budget?.centre.z === b.budget?.centre.z
+    );
+  }
+  return a.fromId === b.fromId && a.toId === b.toId && a.rangePc === b.rangePc && a.ceilingPc === b.ceilingPc;
+}
+
+/** The routing worker, where this environment has one. */
+function startRoutingWorker(): Worker | undefined {
+  return typeof Worker === 'undefined' ? undefined : new Worker(new URL('../../shared/astro/routing.worker', import.meta.url), { type: 'module' });
+}
+
+/**
+ * Asks the route questions of a worker holding its own copy of the catalogue, and hands back
+ * promises.
+ *
+ * The worker answers one request at a time and cannot drop one it has started: a route with no path
+ * can be seconds of work, and a graph of the drawn stars at 8 pc a few hundred milliseconds. So
+ * requests are held here and sent one by one, and while one is out, only the latest of each kind
+ * waits behind it — a newer graph replaces an older one before it is ever built, and the older
+ * promise is rejected with {@link SupersededRequest}. Routes go ahead of graphs, being quick to ask
+ * for and asked for by a click. The same question asked again while it is still outstanding shares
+ * the answer rather than being worked out twice; see `asksTheSame`.
+ *
+ * Where there is no worker — the unit tests' DOM has none, and a worker can fail to load or crash —
+ * the same answers are worked out in place, from the index the scene already holds.
+ */
+export class RoutingClient {
+  private worker?: Worker;
+  private inFlight?: Outstanding;
+  private readonly waiting: Partial<Record<RoutingRequest['kind'], Outstanding>> = {};
+  private nextRequestId = 0;
+
+  constructor(
+    stars: readonly StarRecord[],
+    positions: Float32Array,
+    private readonly localIndex: StarNeighbourhood,
+    startWorker: () => Worker | undefined = startRoutingWorker
+  ) {
+    this.worker = startWorker();
+    if (!this.worker) {
+      return;
+    }
+    this.worker.addEventListener('message', ({ data }: MessageEvent<RoutingResponse>) => this.settle(data));
+    // A worker that fails to load, or dies, answers nothing further: everything outstanding, and
+    // everything asked from here on, is worked out in place instead of waiting for good.
+    this.worker.addEventListener('error', () => this.abandonWorker());
+    this.worker.addEventListener('messageerror', () => this.abandonWorker());
+    // Copies, since the scene goes on using its own; transferred, so the copy is sent and not cloned again.
+    const ids = Int32Array.from(stars, (star) => star.id);
+    const copy = positions.slice();
+    this.worker.postMessage({ kind: 'catalogue', ids, positions: copy }, [ids.buffer, copy.buffer]);
+  }
+
+  route(fromId: number, toId: number, rangePc: number, ceilingPc: number): Promise<RouteAnswer> {
+    return this.ask({ kind: 'route', requestId: this.nextRequestId++, fromId, toId, rangePc, ceilingPc }).then((response) =>
+      response.kind === 'route'
+        ? { route: response.route, neededRangePc: response.neededRangePc, gaveUp: response.gaveUp, least: response.least }
+        : { route: null, neededRangePc: null, gaveUp: false, least: false }
+    );
+  }
+
+  /**
+   * Vertex pairs for every link within `rangePc` between two of the `drawn` stars (catalogue
+   * indices), three floats to an end; only those nearest the budget's centre that fit it, if given.
+   */
+  links(rangePc: number, drawn: Uint32Array, budget?: LinkBudget): Promise<Float32Array> {
+    return this.ask({ kind: 'links', requestId: this.nextRequestId++, rangePc, drawn, budget }).then((response) =>
+      response.kind === 'links' ? response.segments : new Float32Array(0)
+    );
+  }
+
+  dispose(): void {
+    this.worker?.terminate();
+    this.worker = undefined;
+    this.inFlight = undefined;
+    delete this.waiting.route;
+    delete this.waiting.links;
+  }
+
+  private ask(request: RoutingRequest): Promise<RoutingResponse> {
+    if (!this.worker) {
+      return new Promise((resolve) => resolve(answerRouting(this.localIndex, request)));
+    }
+    // Shared rather than replaced: an identical request superseding the one it repeats would reject it,
+    // and whoever holds that promise would take the rejection for its own question.
+    const same = [this.inFlight, this.waiting[request.kind]].find((other) => other !== undefined && asksTheSame(other.request, request));
+    if (same) {
+      return same.promise;
+    }
+    const asked = outstanding(request);
+    this.waiting[request.kind]?.reject(new SupersededRequest());
+    this.waiting[request.kind] = asked;
+    this.sendNext();
+    return asked.promise;
+  }
+
+  private sendNext(): void {
+    if (this.inFlight || !this.worker) {
+      return;
+    }
+    const next = this.waiting.route ?? this.waiting.links;
+    if (!next) {
+      return;
+    }
+    delete this.waiting[next.request.kind];
+    this.inFlight = next;
+    // Cloned, never transferred: a graph's `drawn` is the star field's own list, still drawn and
+    // picked from, and answered in place from should the worker die.
+    this.worker.postMessage(next.request);
+  }
+
+  private settle(response: RoutingResponse): void {
+    const answered = this.inFlight;
+    if (!answered || answered.request.requestId !== response.requestId) {
+      return;
+    }
+    this.inFlight = undefined;
+    if (response.kind === 'failed') {
+      answered.reject(new Error(response.message));
+    } else {
+      answered.resolve(response);
+    }
+    this.sendNext();
+  }
+
+  private abandonWorker(): void {
+    this.worker?.terminate();
+    this.worker = undefined;
+    const stranded = [this.inFlight, this.waiting.route, this.waiting.links];
+    this.inFlight = undefined;
+    delete this.waiting.route;
+    delete this.waiting.links;
+    for (const request of stranded) {
+      if (!request) {
+        continue;
+      }
+      try {
+        request.resolve(answerRouting(this.localIndex, request.request));
+      } catch (error) {
+        request.reject(error instanceof Error ? error : new Error(String(error)));
+      }
+    }
+  }
+}

src/app/features/galaxy-system/star-field-renderer.spec.ts

@@ -172,6 +172,25 @@ describe('StarFieldRenderer', () => {
       renderer.dispose();
     });
 
+    it('ignores a star just outside the frame, however close the pointer gets to the edge', () => {
+      // Its hit area is the drawn size plus a slop, so near an edge that area reaches past the
+      // frame — and a system nobody can see is not one a click should fly into.
+      const offScreen = [star({ id: 9, x: 0, y: 0, z: -10, magnitude: -2 })];
+      const renderer = new StarFieldRenderer(offScreen, packPositions(offScreen));
+      const centre = new THREE.Vector3(0, 0, -10).project(camera);
+      expect(renderer.pickAt(new THREE.Vector2(centre.x, centre.y), camera, camera.aspect)).toBe(9);
+
+      // The same star, just outside the top of the frame: its centre at NDC 1.01, its disc ending at
+      // 1.0033. A click at 0.995 is within its hit radius (0.0167) — so without the frame test this
+      // picks it — while none of the star is on screen.
+      const above = [star({ id: 9, x: 0, y: 10 * Math.tan((camera.fov * Math.PI) / 360) * 1.01, z: -10, magnitude: -2 })];
+      const outside = new StarFieldRenderer(above, packPositions(above));
+
+      expect(outside.pickAt(new THREE.Vector2(0, 0.995), camera, camera.aspect)).toBeUndefined();
+      renderer.dispose();
+      outside.dispose();
+    });
+
     it('picks the star nearest the pointer when several are in view', () => {
       const spread = [
         star({ id: 1, x: 0, y: 0, z: -10 }),
@@ -260,11 +279,6 @@ describe('selectDrawnStars', () => {
     expect(drawn).toEqual([0, 2, 3]);
   });
 
-  it('returns catalogue indices in order, so positions can be subset alongside', () => {
-    const catalogue = Array.from({ length: 100 }, (_, i) => catalogueStar(i, 150, 100 - i));
-    const drawn = Array.from(selectDrawnStars(catalogue, 10));
-    expect(drawn).toEqual([...drawn].sort((a, b) => a - b));
-  });
 });
 
 describe('StarFieldRenderer render budget', () => {
@@ -291,3 +305,212 @@ describe('StarFieldRenderer render budget', () => {
     renderer.dispose();
   });
 });
+
+describe('selectDrawnStars around the view', () => {
+  /** 200 bright stars 240 pc out, enough to spend any small budget on their own. */
+  const brightFar = (from: number) => Array.from({ length: 200 }, (_, i) => catalogueStar(from + i, 240, 2));
+
+  it('draws a faint star near where the view is centred, however far that is from the Sun', () => {
+    const faint = catalogueStar(0, 150, 12);
+    const catalogue = [faint, ...brightFar(1)];
+
+    expect(Array.from(selectDrawnStars(catalogue, 20))).not.toContain(0);
+    expect(Array.from(selectDrawnStars(catalogue, 20, { centre: { x: 150, y: 0, z: 0 } }))).toContain(0);
+  });
+
+  it("keeps the Sun's neighbourhood drawn while the view looks elsewhere", () => {
+    const catalogue = [catalogueStar(0, 1.3, 11), catalogueStar(1, 150, 13), ...brightFar(2)];
+
+    expect(Array.from(selectDrawnStars(catalogue, 20, { centre: { x: 150, y: 0, z: 0 } })).slice(0, 2)).toEqual([1, 0]);
+  });
+
+  it('draws a pinned star wherever it is and however faint', () => {
+    const catalogue = [catalogueStar(0, 240, 14), ...brightFar(1)];
+
+    expect(Array.from(selectDrawnStars(catalogue, 20))).not.toContain(0);
+    expect(Array.from(selectDrawnStars(catalogue, 20, { pinned: [0] }))).toContain(0);
+  });
+
+  it('spends a budget too small for everything on the pinned stars, then the view, then the Sun, then the brightest', () => {
+    const catalogue = [catalogueStar(0, 1, 12), catalogueStar(1, 150, 13), catalogueStar(2, 240, 14), ...brightFar(3)];
+    const focus = { centre: { x: 150, y: 0, z: 0 }, pinned: [2] };
+
+    expect(Array.from(selectDrawnStars(catalogue, 4, focus))).toEqual([2, 1, 0, 3]);
+    expect(Array.from(selectDrawnStars(catalogue, 2, focus))).toEqual([2, 1]);
+  });
+
+  it('keeps the brightest part of a neighbourhood the budget cannot hold whole', () => {
+    const catalogue = [catalogueStar(0, 150, 9), catalogueStar(1, 151, 4), catalogueStar(2, 152, 11), catalogueStar(3, 153, 6), ...brightFar(4)];
+
+    expect(Array.from(selectDrawnStars(catalogue, 2, { centre: { x: 150, y: 0, z: 0 } }))).toEqual([1, 3]);
+  });
+
+  it('draws nothing twice when the view is centred on the Sun or pins a star already near it', () => {
+    const catalogue = [catalogueStar(0, 1, 12), catalogueStar(1, 2, 13), ...brightFar(2)];
+    const drawn = Array.from(selectDrawnStars(catalogue, 10, { centre: { x: 0, y: 0, z: 0 }, pinned: [0, 0, 1] }));
+
+    expect(new Set(drawn).size).toBe(drawn.length);
+    expect(drawn).toHaveLength(10);
+  });
+});
+
+describe('selectDrawnStars in view', () => {
+  /** A star anywhere, with a given apparent magnitude. */
+  const at = (id: number, x: number, y: number, z: number, magnitude: number) => star({ id, x, y, z, magnitude });
+  /** What the camera shows, as the scene hands it over. */
+  const viewOf = (camera: THREE.Camera) => new THREE.Matrix4().multiplyMatrices(camera.projectionMatrix, camera.matrixWorldInverse);
+  /** Bright stars far in front of `testCamera`, spread across its frame. */
+  const brightAhead = (from: number, count = 30) => Array.from({ length: count }, (_, i) => at(from + i, (i - count / 2) * 5, 0, -400, 2));
+  /** Bright stars behind `testCamera`, which only a selection blind to the view would draw. */
+  const brightBehind = (from: number, count = 30) => Array.from({ length: count }, (_, i) => at(from + i, (i - count / 2) * 5, 0, 400, 2));
+
+  it('draws only what is in view, and a pinned star wherever it is', () => {
+    const ahead = Array.from({ length: 5 }, (_, i) => at(i, i * 10, 0, -240, 12));
+    const pinnedBehind = at(5, 0, 0, 240, 14);
+    const catalogue = [...ahead, pinnedBehind, ...brightBehind(6)];
+
+    const drawn = Array.from(selectDrawnStars(catalogue, 20, { pinned: [5], view: viewOf(testCamera()) }));
+
+    expect(drawn).toEqual([5, 0, 1, 2, 3, 4]);
+  });
+
+  it('reaches a quarter of the frame past its edges, and no further', () => {
+    // At 100 pc in front of a 55° camera the frame's half-height is 52 pc: 1.2 of it is 62.5 pc, 1.3 is 67.7.
+    const halfHeight = 100 * Math.tan((55 * Math.PI) / 360);
+    const catalogue = [at(0, 0, 1.2 * halfHeight, -100, 12), at(1, 0, 1.3 * halfHeight, -100, 12), ...brightBehind(2)];
+
+    const drawn = Array.from(selectDrawnStars(catalogue, 20, { view: viewOf(testCamera()) }));
+
+    expect(drawn).toEqual([0]);
+  });
+
+  it("draws the neighbourhood of the view's centre ahead of brighter stars, but only the part in view", () => {
+    const camera = new THREE.PerspectiveCamera(55, 16 / 9, 0.01, 5000);
+    camera.position.set(0, 0, -140);
+    camera.lookAt(0, 0, -1000);
+    camera.updateMatrixWorld(true);
+    const memberAhead = at(0, 0, 0, -160, 14);
+    const memberBehind = at(1, 0, 0, -130, 14);
+    const catalogue = [memberAhead, memberBehind, ...Array.from({ length: 30 }, (_, i) => at(2 + i, (i - 15) * 5, 0, -600, 2))];
+
+    const drawn = Array.from(selectDrawnStars(catalogue, 20, { centre: { x: 0, y: 0, z: -150 }, view: viewOf(camera) }));
+
+    expect(drawn[0]).toBe(0);
+    expect(drawn).not.toContain(1);
+  });
+
+  it('draws the planet hosts in view first after the pinned stars, and not those out of view', () => {
+    const hostAhead = at(0, 0, 0, -240, 14);
+    const hostBehind = at(1, 0, 0, 240, 14);
+    const nearSun = at(2, 0, 0, -10, 13);
+    const catalogue = [hostAhead, hostBehind, nearSun, ...brightAhead(3)];
+    const hosts = Uint8Array.from(catalogue, (_, index) => (index < 2 ? 1 : 0));
+
+    const drawn = Array.from(selectDrawnStars(catalogue, 3, { hosts, view: viewOf(testCamera()) }));
+
+    expect(drawn).toEqual([0, 2, 3]);
+  });
+
+  it('frames a plan view as a box, however deep: behind the camera included', () => {
+    const plan = new THREE.OrthographicCamera(-10, 10, 10, -10, -5000, 5000);
+    plan.position.set(0, 0, 0);
+    plan.lookAt(0, 0, -1);
+    plan.updateMatrixWorld(true);
+    const catalogue = [at(0, 0, 0, 50, 12), at(1, 12, 0, -50, 12), at(2, 13, 0, -50, 12), ...Array.from({ length: 30 }, (_, i) => at(3 + i, 500, i, 0, 2))];
+
+    const drawn = Array.from(selectDrawnStars(catalogue, 20, { view: viewOf(plan) }));
+
+    expect(drawn).toEqual([0, 1]);
+  });
+});
+
+describe('StarFieldRenderer refocus', () => {
+  const camera = testCamera();
+  /** A faint star straight ahead, 150 pc out, among bright ones well off to the side. */
+  const faintAhead = star({ id: 77, x: 0, y: 0, z: -150, magnitude: 13, colorIndex: 1.9 });
+  const catalogue = [faintAhead, ...Array.from({ length: 50 }, (_, i) => star({ id: 100 + i, x: 60, y: i, z: -40, magnitude: 1, colorIndex: -0.3 + i * 0.04 }))];
+  const positions = packPositions(catalogue);
+
+  it('draws and picks a faint star once the view is centred near it', () => {
+    const renderer = new StarFieldRenderer(catalogue, positions, 10);
+    expect(renderer.pickAt(new THREE.Vector2(0, 0), camera, camera.aspect)).toBeUndefined();
+
+    renderer.refocus({ centre: { x: 0, y: 0, z: -140 } });
+
+    expect(renderer.pickAt(new THREE.Vector2(0, 0), camera, camera.aspect)).toBe(77);
+    expect((renderer.object.geometry as THREE.InstancedBufferGeometry).instanceCount).toBe(renderer.drawnCount);
+    renderer.dispose();
+  });
+
+  it('draws a pinned star, and passes over an index past the end of the catalogue', () => {
+    const renderer = new StarFieldRenderer(catalogue, positions, 10);
+
+    renderer.refocus({ pinned: [123456, 0] });
+
+    const drawnIds = Array.from({ length: renderer.drawnCount }, (_, i) => renderer.starIdAt(i));
+    expect(drawnIds).toContain(77);
+    expect(renderer.drawnCount).toBe(10);
+    renderer.dispose();
+  });
+
+  it('gives each drawn star its own colour and size, wherever the refocus put it', () => {
+    const renderer = new StarFieldRenderer(catalogue, positions, 10);
+    renderer.refocus({ centre: { x: 0, y: 0, z: -140 }, pinned: [21] });
+    const { colorAttribute, sizeAttribute } = renderer as unknown as { colorAttribute: THREE.InstancedBufferAttribute; sizeAttribute: THREE.InstancedBufferAttribute };
+
+    for (let instance = 0; instance < renderer.drawnCount; instance++) {
+      const drawnStar = catalogue.find((candidate) => candidate.id === renderer.starIdAt(instance))!;
+      const expected = colorIndexToRgb(drawnStar.colorIndex, drawnStar.spectralType);
+      expect(colorAttribute.getX(instance)).toBeCloseTo(expected.r, 5);
+      expect(colorAttribute.getZ(instance)).toBeCloseTo(expected.b, 5);
+      expect(sizeAttribute.getX(instance)).toBeGreaterThan(0);
+    }
+    const faintSlot = Array.from({ length: renderer.drawnCount }, (_, i) => renderer.starIdAt(i)).indexOf(77);
+    const brightSlot = Array.from({ length: renderer.drawnCount }, (_, i) => renderer.starIdAt(i)).indexOf(120);
+    expect(sizeAttribute.getX(brightSlot)).toBeGreaterThan(sizeAttribute.getX(faintSlot));
+    renderer.dispose();
+  });
+
+  it('leaves the buffers alone when the drawn set has not changed, and rewrites them when it has', () => {
+    const renderer = new StarFieldRenderer(catalogue, positions, 10);
+    const { positionAttribute } = renderer as unknown as { positionAttribute: THREE.InstancedBufferAttribute };
+    const version = positionAttribute.version;
+
+    renderer.refocus({ centre: { x: 0, y: 0, z: 0 } });
+    expect(positionAttribute.version).toBe(version);
+
+    renderer.refocus({ centre: { x: 0, y: 0, z: -140 } });
+    expect(positionAttribute.version).toBeGreaterThan(version);
+    renderer.dispose();
+  });
+
+  it('drops a star from the drawn set, and from picking, once the view has moved away from it', () => {
+    // The subtle failure this guards: buffers rewritten for a new selection while picking still
+    // reads the old one would leave clickable ghosts where nothing is drawn.
+    const renderer = new StarFieldRenderer(catalogue, positions, 10);
+    renderer.refocus({ centre: { x: 0, y: 0, z: -140 } });
+    expect(renderer.pickAt(new THREE.Vector2(0, 0), camera, camera.aspect)).toBe(77);
+
+    renderer.refocus({ centre: { x: 0, y: 0, z: 0 } });
+
+    expect(renderer.pickAt(new THREE.Vector2(0, 0), camera, camera.aspect)).toBeUndefined();
+    expect(Array.from({ length: renderer.drawnCount }, (_, i) => renderer.starIdAt(i))).not.toContain(77);
+    renderer.dispose();
+  });
+
+  it('drops a star from the drawn set, and from picking, once the camera has turned away from it', () => {
+    const renderer = new StarFieldRenderer(catalogue, positions, 10);
+    const view = (from: THREE.Camera) => new THREE.Matrix4().multiplyMatrices(from.projectionMatrix, from.matrixWorldInverse);
+    renderer.refocus({ centre: { x: 0, y: 0, z: -140 }, view: view(camera) });
+    expect(renderer.pickAt(new THREE.Vector2(0, 0), camera, camera.aspect)).toBe(77);
+
+    const turned = testCamera();
+    turned.lookAt(0, 0, 1);
+    turned.updateMatrixWorld(true);
+    renderer.refocus({ centre: { x: 0, y: 0, z: -140 }, view: view(turned) });
+
+    expect(renderer.pickAt(new THREE.Vector2(0, 0), camera, camera.aspect)).toBeUndefined();
+    expect(Array.from({ length: renderer.drawnCount }, (_, i) => renderer.starIdAt(i))).not.toContain(77);
+    renderer.dispose();
+  });
+});

src/app/features/galaxy-system/star-field-renderer.ts

@@ -1,6 +1,7 @@
 import * as THREE from 'three/webgpu';
 import { float, instancedBufferAttribute, mix, modelViewMatrix, smoothstep, uniform, uv, vec2, vec4 } from 'three/tsl';
 
+import { BrightnessIndex, brightnessIndex, Positioned } from '../../shared/astro/brightest';
 import { spectralTypeToColorIndex } from '../../shared/astro/spectral';
 import { SceneCamera } from '../../core/engine/engine.service';
 import { StarRecord } from '../../shared/models/star.model';
@@ -25,25 +26,25 @@ const PICK_NDC_SLOP = 0.01;
 /**
  * How many stars the field draws at once, however many the catalogue holds.
  *
- * The catalogue reaches as far as its parallaxes do — 68388 stars at 250 pc — but drawing all of
+ * The *data* is the catalogue and the *drawing* is a budget, and the two are allowed to differ:
- * them is a cost paid every frame by every machine, and most of that cost buys 1.5-pixel dots.
+ * everything still exists for search, for flying to, and for hosting planets. Which stars fill
- * So the *data* is the catalogue and the *drawing* is a budget, and the two are allowed to
+ * the budget follows the view; see {@link selectDrawnStars}.
- * differ. Everything still exists for search, for flying to, and for hosting planets.
  *
- * Currently set to the whole catalogue, which is what a GPU should be asked to do — this is one
+ * The number is set by what the field looks like, before what it costs. The catalogue is
- * instanced draw call, and a discrete card will not notice it. The budget still exists because
+ * 423 651 stars since Gaia, and drawn whole the opening view is a grey wash: the additive
- * the catalogue is meant to grow past what any machine should draw at once: Gaia alone could
+ * blending of that many 1.5-pixel dots buries the labels, the rings on the planet hosts and the
- * contribute a million stars, and at that point the selection below is what keeps the field
+ * grid. At 150 000 the wash has begun; at this budget the view reads. Measured at 1920 × 1080 on
- * legible rather than a grey wash.
+ * a Ryzen 7700X, the cost argues the same way. An RTX 4080 draws the whole catalogue in the same
- *
+ * 6.1 ms a frame as this budget, so a discrete card does not notice. The processor's own
- * Machines without a GPU do feel it. A software rasterizer measured here lost about a third of
+ * two-core Radeon, standing in for an entry-level laptop, pays about 4 ms a frame for every
- * its frame rate per 12000 stars drawn; if that matters for a deployment, this is the one number
+ * 100 000 stars: 112 frames a second at this budget, 44 at the whole catalogue, and the same
- * to turn down.
+ * again under the WebGL2 fallback.
  */
-export const STAR_RENDER_BUDGET = 68388;
+export const STAR_RENDER_BUDGET = 70_000;
 
 /**
- * Radius (parsecs) inside which every star is drawn regardless of brightness.
+ * Radius (parsecs) around the Sun, and around wherever the view is centred, inside which every
+ * star in view is drawn regardless of brightness.
  *
  * A pure brightness cut would be defensible — apparent magnitude is exactly "how visible this
  * is" — but it would drop the solar neighbourhood, because the nearest stars are overwhelmingly
@@ -51,11 +52,50 @@ export const STAR_RENDER_BUDGET = 68388;
  * and the ones that hold the nearby planets, so the neighbourhood is kept whole and the budget
  * is spent on the brightest of everything beyond it.
  *
- * Kept deliberately small against the catalogue's 250 pc reach. The guaranteed core occupies a
+ * The same holds wherever the view is looking. Before the drawn set followed the view, a region
- * thousandth of that volume, so a generous radius spends most of the budget inside it and draws
+ * 150 pc out drew 49 of the 442 stars within this radius of it, and a route plotted there ran
- * a dense knot surrounded by nothing — which is a worse picture than the smaller catalogue was.
+ * through waypoints nobody could see or click: Sol to Almach at 8 pc passed 19 stars and drew 6.
+ *
+ * Kept deliberately small against the catalogue's reach. Around the Sun it holds 3 654 stars;
+ * a generous radius spends most of the budget inside it and draws a dense knot surrounded by
+ * nothing.
  */
-export const ALWAYS_DRAWN_RADIUS_PC = 25;
+export const FOCUS_RADIUS_PC = 25;
+
+/**
+ * How far past the edges of the frame the drawn stars reach, as a share of the frame's half-width
+ * and half-height: 5° beyond the top and bottom at the 50° field of view, 6° beyond each side.
+ *
+ * The drawn set is chosen for a camera pose and kept until the view has turned or moved half this
+ * far, so the margin is what is on screen by the time it is chosen again. Wider stays whole
+ * through faster turns but spends the budget off screen: at 30 pc from the Sun, where the budget
+ * binds, 0.25 leaves 52 000 of the 70 000 on screen and 0.5 only 44 000.
+ */
+export const VIEW_MARGIN = 0.25;
+
+/** What, besides the brightest stars, the field should be sure to draw. */
+export interface DrawFocus {
+  /** Where the view is centred. Its neighbourhood is drawn whole, like the Sun's. */
+  readonly centre?: Positioned;
+  /**
+   * Catalogue indices drawn wherever they are and however faint: the selected star, the stars
+   * of a plotted route. Anything the map points at has to be there to be pointed at.
+   */
+  readonly pinned?: readonly number[];
+  /**
+   * 1 for each catalogue index with known planets. Drawn next after the pinned stars, however
+   * faint: each carries a ring, and a ring around a star that is not drawn circles nothing that
+   * can be clicked.
+   */
+  readonly hosts?: Uint8Array;
+  /**
+   * The camera's projection times its view matrix. Only stars inside its frame, widened by
+   * {@link VIEW_MARGIN}, are drawn, pinned stars aside; without it, the whole sky is in view.
+   */
+  readonly view?: THREE.Matrix4;
+}
+
+const SUN: Positioned = { x: 0, y: 0, z: 0 };
 
 const COLD_STAR_COLOR = new THREE.Color(0.65, 0.75, 1.0);
 const NEUTRAL_STAR_COLOR = new THREE.Color(1.0, 1.0, 1.0);
@@ -101,7 +141,99 @@ function createQuadGeometry(instanceCount: number): THREE.InstancedBufferGeometr
 }
 
 /**
- * Builds the galaxy-scale star field as instanced camera-facing billboards, one per HYG star,
+ * Reads a render budget override off the page URL (`?stars=20000`), falling back to the default.
+ *
+ * Two uses, one real and one incidental. The real one is a deployment or a machine that cannot
+ * draw the whole catalogue — a number in a URL beats a rebuild. The incidental one is the
+ * end-to-end suite, which runs against a software rasterizer whose frame rate is two orders of
+ * magnitude below a real GPU's: those tests are checking navigation and state, and making them
+ * wait on a rasterizer measures nothing about the app.
+ */
+export function starRenderBudgetFromUrl(search: string, fallback = STAR_RENDER_BUDGET): number {
+  const requested = Number(new URLSearchParams(search).get('stars'));
+  return Number.isFinite(requested) && requested > 0 ? Math.floor(requested) : fallback;
+}
+
+/**
+ * Chooses which stars to draw when the catalogue is larger than the budget. In order, until the
+ * budget is spent: the pinned stars wherever they are, then of the stars in view, the planet
+ * hosts, everything within {@link FOCUS_RADIUS_PC} of where the view is centred, everything within
+ * it of the Sun, and the brightest of the rest. Each tier is taken brightest first, so a budget too
+ * small to hold one whole keeps its most visible part.
+ *
+ * Returns indices into the original list, in the order they were chosen. `index` is the
+ * catalogue's brightness index, passed in when the caller already has it rather than sorted again
+ * on every call.
+ */
+export function selectDrawnStars(
+  stars: readonly StarRecord[],
+  budget = STAR_RENDER_BUDGET,
+  focus: DrawFocus = {},
+  index: BrightnessIndex = brightnessIndex(stars)
+): Uint32Array {
+  if (stars.length <= budget) {
+    return Uint32Array.from(stars.keys());
+  }
+
+  // One walk of the brightness order, reading positions laid out in that order, sorts each tier
+  // brightest first as it goes: 2.4-3.1 ms on the real catalogue in Node, against 6.4-8.5 ms
+  // gathering both neighbourhoods in catalogue order and sorting them. Of the stars in no earlier
+  // tier only the first `budget` in view can ever be taken, so past those it looks for the tiers.
+  const { order, positions } = index;
+  const radiusSq = FOCUS_RADIUS_PC * FOCUS_RADIUS_PC;
+  const centre = focus.centre ?? SUN;
+  const view = focus.view?.elements;
+  const reachScale = 1 + VIEW_MARGIN;
+  const hosts: number[] = [];
+  const nearCentre: number[] = [];
+  const nearSun: number[] = [];
+  const rest: number[] = [];
+  for (let at = 0; at < order.length; at++) {
+    const x = positions[at * 3];
+    const y = positions[at * 3 + 1];
+    const z = positions[at * 3 + 2];
+    const dx = x - centre.x;
+    const dy = y - centre.y;
+    const dz = z - centre.z;
+    const isHost = focus.hosts?.[order[at]] === 1;
+    const inCentre = dx * dx + dy * dy + dz * dz <= radiusSq;
+    const inSun = x * x + y * y + z * z <= radiusSq;
+    if (!isHost && !inCentre && !inSun && rest.length >= budget) {
+      continue;
+    }
+    if (view) {
+      // In clip space: in frame when |x| and |y| are within w, widened by the margin. Behind a
+      // perspective camera w is negative, so nothing there passes; an orthographic camera's w is 1.
+      const reach = (view[3] * x + view[7] * y + view[11] * z + view[15]) * reachScale;
+      if (Math.abs(view[0] * x + view[4] * y + view[8] * z + view[12]) > reach || Math.abs(view[1] * x + view[5] * y + view[9] * z + view[13]) > reach) {
+        continue;
+      }
+    }
+    (isHost ? hosts : inCentre ? nearCentre : inSun ? nearSun : rest).push(order[at]);
+  }
+
+  const chosen = new Uint8Array(stars.length);
+  const selected: number[] = [];
+  const take = (index: number): void => {
+    if (!chosen[index] && selected.length < budget) {
+      chosen[index] = 1;
+      selected.push(index);
+    }
+  };
+  for (const pinned of focus.pinned ?? []) {
+    if (pinned >= 0 && pinned < stars.length) {
+      take(pinned);
+    }
+  }
+  hosts.forEach(take);
+  nearCentre.forEach(take);
+  nearSun.forEach(take);
+  rest.forEach(take);
+  return Uint32Array.from(selected);
+}
+
+/**
+ * Builds the galaxy-scale star field as instanced camera-facing billboards, one per drawn star,
  * coloured by spectral index and sized by magnitude.
  *
  * **Why billboards and not `THREE.Points`.** Point primitives are capped at a single pixel on
@@ -116,50 +248,12 @@ function createQuadGeometry(instanceCount: number): THREE.InstancedBufferGeometr
  * Sizes are angular (`sizeAttenuation = false`), so a star holds the same apparent size however
  * close the camera gets. That is deliberate and physically right: real stars are unresolvable
  * point sources, and their apparent size on screen is a function of brightness, not distance.
- */
-/**
- * Chooses which stars to draw when the catalogue is larger than the budget: everything inside
- * the neighbourhood radius, then the brightest of the rest until the budget is spent.
  *
- * Returns indices into the original list, so the caller can subset the positions that go with
+ * The instance buffers hold the budget, not the catalogue, and are rewritten in place when
- * them. Returns them in catalogue order rather than in selection order, purely so the drawn set
+ * {@link refocus} changes which stars fill it.
- * is stable and inspectable.
  */
-/**
- * Reads a render budget override off the page URL (`?stars=20000`), falling back to the default.
- *
- * Two uses, one real and one incidental. The real one is a deployment or a machine that cannot
- * draw the whole catalogue — a number in a URL beats a rebuild. The incidental one is the
- * end-to-end suite, which runs against a software rasterizer whose frame rate is two orders of
- * magnitude below a real GPU's: those tests are checking navigation and state, and making them
- * wait on a rasterizer measures nothing about the app.
- */
-export function starRenderBudgetFromUrl(search: string, fallback = STAR_RENDER_BUDGET): number {
-  const requested = Number(new URLSearchParams(search).get('stars'));
-  return Number.isFinite(requested) && requested > 0 ? Math.floor(requested) : fallback;
-}
-
-export function selectDrawnStars(stars: readonly StarRecord[], budget = STAR_RENDER_BUDGET): Uint32Array {
-  if (stars.length <= budget) {
-    return Uint32Array.from(stars.keys());
-  }
-
-  const near: number[] = [];
-  const far: number[] = [];
-  stars.forEach((star, index) => {
-    (Math.hypot(star.x, star.y, star.z) <= ALWAYS_DRAWN_RADIUS_PC ? near : far).push(index);
-  });
-
-  far.sort((a, b) => stars[a].magnitude - stars[b].magnitude);
-  const selected = near.concat(far.slice(0, Math.max(0, budget - near.length)));
-  selected.sort((a, b) => a - b);
-  return Uint32Array.from(selected);
-}
-
 export class StarFieldRenderer {
   readonly object: THREE.Mesh;
-  /** How many of the catalogue's stars this field actually draws. */
-  readonly drawnCount: number;
 
   /** 1 under a perspective camera, 0 under an orthographic one. See `setProjection`. */
   private readonly perspective = uniform(1);
@@ -167,39 +261,47 @@ export class StarFieldRenderer {
 
   private readonly geometry: THREE.InstancedBufferGeometry;
   private readonly material: THREE.SpriteNodeMaterial;
-  /** The subset of the catalogue that is drawn, and so the only set that can be clicked. */
+  private readonly budget: number;
-  private readonly stars: readonly StarRecord[];
+  private readonly brightness: BrightnessIndex;
-  /** Angular diameter per drawn star, in the same order as `stars` — reused for picking. */
+  /**
-  private readonly angularSizes: Float32Array;
+   * Colour and angular size of every star in the catalogue, worked out once: a refocus then only
+   * copies them into the instances, 0.7 ms for the budget rather than 5.6 ms computing them again.
+   */
+  private readonly catalogueColors: Float32Array;
+  private readonly catalogueSizes: Float32Array;
 
-  constructor(catalogue: readonly StarRecord[], cataloguePositions: Float32Array, budget = STAR_RENDER_BUDGET) {
+  /** Per-instance data, `budget` long; the first `drawnCount` entries are live. */
-    const drawn = selectDrawnStars(catalogue, budget);
+  private readonly positionAttribute: THREE.InstancedBufferAttribute;
-    this.stars = drawn.length === catalogue.length ? catalogue : Array.from(drawn, (index) => catalogue[index]);
+  private readonly colorAttribute: THREE.InstancedBufferAttribute;
-    this.drawnCount = this.stars.length;
+  private readonly sizeAttribute: THREE.InstancedBufferAttribute;
+  /** Catalogue index behind each live instance: the set that is drawn, and so the only set that can be clicked. */
+  private drawn: Uint32Array = new Uint32Array(0);
 
-    const stars = this.stars;
+  constructor(
-    this.geometry = createQuadGeometry(stars.length);
+    private readonly catalogue: readonly StarRecord[],
+    private readonly cataloguePositions: Float32Array,
+    budget = STAR_RENDER_BUDGET,
+    brightness?: BrightnessIndex
+  ) {
+    this.budget = budget;
+    this.brightness = brightness ?? brightnessIndex(catalogue);
+    const capacity = Math.min(budget, catalogue.length);
+    this.geometry = createQuadGeometry(0);
 
-    const colors = new Float32Array(stars.length * 3);
+    this.positionAttribute = new THREE.InstancedBufferAttribute(new Float32Array(capacity * 3), 3);
-    this.angularSizes = new Float32Array(stars.length);
+    this.colorAttribute = new THREE.InstancedBufferAttribute(new Float32Array(capacity * 3), 3);
-    // Repacked only when the drawn set is a subset; otherwise the ETL's buffer is used as-is.
+    this.sizeAttribute = new THREE.InstancedBufferAttribute(new Float32Array(capacity), 1);
-    const positions =
-      drawn.length === catalogue.length
-        ? cataloguePositions
-        : Float32Array.from({ length: drawn.length * 3 }, (_, i) => cataloguePositions[drawn[(i / 3) | 0] * 3 + (i % 3)]);
 
-    stars.forEach((star, index) => {
+    this.catalogueColors = new Float32Array(catalogue.length * 3);
+    this.catalogueSizes = new Float32Array(catalogue.length);
+    catalogue.forEach((star, index) => {
       const color = colorIndexToRgb(star.colorIndex, star.spectralType);
-      colors[index * 3] = color.r;
+      this.catalogueColors[index * 3] = color.r;
-      colors[index * 3 + 1] = color.g;
+      this.catalogueColors[index * 3 + 1] = color.g;
-      colors[index * 3 + 2] = color.b;
+      this.catalogueColors[index * 3 + 2] = color.b;
-      this.angularSizes[index] = magnitudeToPointSize(star.magnitude) * PIXELS_TO_ANGULAR_SIZE;
+      this.catalogueSizes[index] = magnitudeToPointSize(star.magnitude) * PIXELS_TO_ANGULAR_SIZE;
     });
 
-    const positionAttribute = new THREE.InstancedBufferAttribute(positions, 3);
-    const colorAttribute = new THREE.InstancedBufferAttribute(colors, 3);
-    const sizeAttribute = new THREE.InstancedBufferAttribute(this.angularSizes, 1);
-
     this.material = new THREE.SpriteNodeMaterial({
       transparent: true,
       depthWrite: false,
@@ -212,15 +314,15 @@ export class StarFieldRenderer {
     // a thousandth of a parsec — invisible. Doing the same arithmetic in the node graph, behind
     // a uniform, lets one material serve both cameras without being recompiled between them.
     this.material.sizeAttenuation = true;
-    const position = instancedBufferAttribute<'vec3'>(positionAttribute, 'vec3');
+    const position = instancedBufferAttribute<'vec3'>(this.positionAttribute, 'vec3');
-    const angularSize = instancedBufferAttribute<'float'>(sizeAttribute, 'float');
+    const angularSize = instancedBufferAttribute<'float'>(this.sizeAttribute, 'float');
     this.material.positionNode = position;
     // Perspective: a star's world size is its angular size times how far away it is, which is
     // exactly what the built-in does. Orthographic: distance does not set apparent size at all,
     // the frustum does, so the same angular size is scaled by the frustum instead.
     const viewDepth = modelViewMatrix.mul(vec4(position, 1)).z.negate();
     this.material.scaleNode = angularSize.mul(mix(this.orthographicScale, viewDepth, this.perspective));
-    this.material.colorNode = instancedBufferAttribute<'vec3'>(colorAttribute, 'vec3');
+    this.material.colorNode = instancedBufferAttribute<'vec3'>(this.colorAttribute, 'vec3');
     // Soft radial falloff so each star is a small bright core inside a halo, rather than a
     // hard-edged square. `uv` runs 0..1 across the quad, so 0.5 is its centre.
     const radius = uv().sub(vec2(0.5)).length();
@@ -230,6 +332,51 @@ export class StarFieldRenderer {
     // The quad's own bounds sit at the origin and say nothing about where the instances are,
     // so leaving culling on would drop the whole field whenever the origin left the frustum.
     this.object.frustumCulled = false;
+
+    this.refocus({});
+  }
+
+  /** How many of the catalogue's stars this field is drawing. */
+  get drawnCount(): number {
+    return this.drawn.length;
+  }
+
+  /**
+   * The catalogue indices being drawn. Replaced by a refocus that changes them, never changed in
+   * place, so the same array means the same stars.
+   */
+  get drawnStars(): Uint32Array {
+    return this.drawn;
+  }
+
+  /**
+   * Chooses the drawn stars again for where the view now is, and rewrites the instance buffers
+   * with them. See {@link selectDrawnStars}.
+   */
+  refocus(focus: DrawFocus): void {
+    const drawn = selectDrawnStars(this.catalogue, this.budget, focus, this.brightness);
+    // The same stars in the same instances: the buffers already hold them, and a rewrite would
+    // upload 2 MB to the GPU for nothing — which a pan across empty space would do every pass.
+    if (drawn.length === this.drawn.length && drawn.every((index, instance) => index === this.drawn[instance])) {
+      return;
+    }
+    this.drawn = drawn;
+
+    const positions = this.positionAttribute.array as Float32Array;
+    const colors = this.colorAttribute.array as Float32Array;
+    const sizes = this.sizeAttribute.array as Float32Array;
+    this.drawn.forEach((catalogueIndex, instance) => {
+      for (let axis = 0; axis < 3; axis++) {
+        positions[instance * 3 + axis] = this.cataloguePositions[catalogueIndex * 3 + axis];
+        colors[instance * 3 + axis] = this.catalogueColors[catalogueIndex * 3 + axis];
+      }
+      sizes[instance] = this.catalogueSizes[catalogueIndex];
+    });
+
+    this.geometry.instanceCount = this.drawn.length;
+    this.positionAttribute.needsUpdate = true;
+    this.colorAttribute.needsUpdate = true;
+    this.sizeAttribute.needsUpdate = true;
   }
 
   /**
@@ -245,9 +392,9 @@ export class StarFieldRenderer {
     this.orthographicScale.value = halfHeightWorld === null ? 0 : halfHeightWorld / Math.tan((REFERENCE_FOV_DEGREES * Math.PI) / 360);
   }
 
-  /** Looks up the HYG star id for a given instance index. */
+  /** Looks up the star id for a given instance index. */
   starIdAt(instanceIndex: number): number | undefined {
-    return this.stars[instanceIndex]?.id;
+    return instanceIndex >= 0 && instanceIndex < this.drawn.length ? this.catalogue[this.drawn[instanceIndex]].id : undefined;
   }
 
   /**
@@ -259,6 +406,11 @@ export class StarFieldRenderer {
    * needed: each star is tested against the size it is actually drawn at, so the hit area matches
    * what the user sees at every zoom level instead of being over-permissive up close and
    * sub-pixel at the far end of the camera's range.
+   *
+   * Only stars on screen can be picked. The hit area is the drawn size plus a slop of
+   * {@link PICK_NDC_SLOP}, and near an edge that slop reaches past the frame: a click in the
+   * last few pixels of the view used to be able to fly into a system whose star was outside it,
+   * with nothing on screen to explain where it had gone.
    */
   pickAt(pointerNdc: THREE.Vector2, camera: SceneCamera, aspect: number): number | undefined {
     // What a unit of angular size is worth on screen. Under perspective the field of view sets
@@ -269,22 +421,29 @@ export class StarFieldRenderer {
     const perspective = (camera as THREE.PerspectiveCamera).isPerspectiveCamera;
     const tanHalfFov = Math.tan(((perspective ? (camera as THREE.PerspectiveCamera).fov : REFERENCE_FOV_DEGREES) * Math.PI) / 360);
     const projected = new THREE.Vector3();
+    const positions = this.positionAttribute.array as Float32Array;
+    const sizes = this.sizeAttribute.array as Float32Array;
 
     let bestIndex: number | undefined;
     let bestScore = Infinity;
 
-    for (let index = 0; index < this.stars.length; index++) {
+    for (let index = 0; index < this.drawn.length; index++) {
-      const star = this.stars[index];
+      projected.set(positions[index * 3], positions[index * 3 + 1], positions[index * 3 + 2]).project(camera);
-      projected.set(star.x, star.y, star.z).project(camera);
       // Outside the depth range means behind the camera or beyond the far plane; `project`
       // mirrors points behind the camera onto the screen, so this guard is load-bearing.
       if (projected.z < -1 || projected.z > 1) {
         continue;
       }
-
       // A sprite square in view space projects to an ellipse in NDC: the same half-extent in y,
       // divided by the aspect ratio in x. Scaling dx by the aspect makes the comparison circular.
-      const ndcRadius = (0.5 * this.angularSizes[index]) / tanHalfFov + PICK_NDC_SLOP;
+      const drawnRadius = (0.5 * sizes[index]) / tanHalfFov;
+      // Off screen if no part of the drawn disc is inside the frame. Tested before the slop is
+      // added: the slop is forgiveness for an imprecise click on a star you can see, not a reach
+      // past the edge to one you cannot.
+      if (Math.abs(projected.x) - drawnRadius / aspect > 1 || Math.abs(projected.y) - drawnRadius > 1) {
+        continue;
+      }
+      const ndcRadius = drawnRadius + PICK_NDC_SLOP;
       const dx = (projected.x - pointerNdc.x) * aspect;
       const dy = projected.y - pointerNdc.y;
       const score = Math.hypot(dx, dy) / ndcRadius;
@@ -295,7 +454,7 @@ export class StarFieldRenderer {
       }
     }
 
-    return bestIndex === undefined ? undefined : this.stars[bestIndex].id;
+    return bestIndex === undefined ? undefined : this.starIdAt(bestIndex);
   }
 
   dispose(): void {

src/app/features/galaxy-system/starmap-hud.component.spec.ts

@@ -79,4 +79,17 @@ describe('StarmapHudComponent', () => {
     // An empty nameplate is worse than none: it reads as a selection that failed to resolve.
     expect(render('galaxy').querySelector('[data-testid="hud-banner"]')).toBeNull();
   });
+
+  it('shows the scale it is given, as a bar of that width', () => {
+    fixture.componentRef.setInput('scale', { label: '10 pc', widthPx: 100 });
+    const bar = render('galaxy').querySelector<HTMLElement>('[data-testid="hud-scale"]');
+
+    expect(bar?.getAttribute('aria-label')).toBe('Scale: 10 pc');
+    expect(bar?.textContent?.trim()).toBe('10 pc');
+    expect(bar?.querySelector<HTMLElement>('span:last-child')?.style.width).toBe('100px');
+  });
+
+  it('shows no scale bar while there is no scale to show', () => {
+    expect(render('galaxy').querySelector('[data-testid="hud-scale"]')).toBeNull();
+  });
 });

src/app/features/galaxy-system/starmap-hud.component.ts

@@ -1,5 +1,6 @@
 import { ChangeDetectionStrategy, Component, computed, input, output } from '@angular/core';
 
+import { ScaleBar } from '../../shared/format/scale-bar';
 import { ViewLevel } from '../../shared/state/navigation.store';
 import { ReticleIconComponent } from '../../shared/ui/reticle-icon.component';
 
@@ -20,9 +21,9 @@ const LADDER: readonly { level: ViewLevel; label: string }[] = [
 ];
 
 /**
- * The top of the map's heads-up display: the scale ladder on the left, the nameplate across
+ * The top of the map's heads-up display: the scale ladder on the left with the scale bar under
- * the centre, and a centre reticle on whatever the camera is holding. Readouts and tools live
+ * it, the nameplate across the centre, and a centre reticle on whatever the camera is holding.
- * in the dock along the bottom (`HudDockComponent`).
+ * Readouts and tools live in the dock along the bottom (`HudDockComponent`).
  *
  * Purely presentational — every value arrives as an input and the only thing it emits is a
  * request to move to another scale. The scene owns the camera and decides what that means.
@@ -68,6 +69,15 @@ const LADDER: readonly { level: ViewLevel; label: string }[] = [
       }
     </nav>
 
+    @if (scale(); as bar) {
+      <!-- The map's scale bar, under the rail that names the scale: a round length, measured at the
+           depth the view is centred on, since under perspective every depth has its own. -->
+      <div data-testid="hud-scale" role="img" [attr.aria-label]="'Scale: ' + bar.label" class="absolute top-16 left-6 flex flex-col items-start gap-1">
+        <span class="type-label text-muted tabular-nums">{{ bar.label }}</span>
+        <span class="block h-1.5 border-x border-b border-accent/70" [style.width.px]="bar.widthPx"></span>
+      </div>
+    }
+
     @if (title()) {
       <!-- Hidden below lg: the readout panel names the same thing, and at narrower widths a
            long star name runs into the scale rail on its left and under the object card on its
@@ -86,6 +96,8 @@ export class StarmapHudComponent {
   /** What the view is holding, for the nameplate — the selected star, or nothing. */
   readonly title = input('');
   readonly showReticle = input(true);
+  /** The scale bar for the current zoom, worked out by the scene, which knows the camera. */
+  readonly scale = input<ScaleBar | null>(null);
 
   readonly levelSelected = output<ViewLevel>();
 

src/app/features/galaxy-system/system-framing.spec.ts

@@ -5,7 +5,6 @@ import { eclipticToEquatorial, OBLIQUITY_J2000_DEG } from '../../shared/astro/co
 import {
   bodyMarkerRadiusAu,
   DEFAULT_STAR_MARKER_RADIUS_AU,
-  starGlowExtentAu,
   starMarkerRadiusAu,
   systemFrameRadiusAu,
   systemFramingDistanceAu,
@@ -113,105 +112,6 @@ describe('systemFramingDistanceAu', () => {
   });
 });
 
-describe('starGlowExtentAu', () => {
-  /** A typical viewport, so a screen-space claim can be made in pixels rather than in ratios. */
-  const REFERENCE_VIEWPORT_HALF_HEIGHT_PX = 450;
-
-  /** The halo's visual radius, in AU, at the distance this system is framed from. */
-  function haloRadiusAu(innermostAu: number, outermostAu: number, glowScale = 1): number {
-    // The sprite's extent is its full width, so half of it is what reaches out from the star.
-    return starGlowExtentAu(starMarkerRadiusAu(innermostAu), frameRadiusFor(outermostAu), glowScale) / 2;
-  }
-
-  function frameRadiusFor(outermostAu: number): number {
-    const rings = systemGridRingsAu(outermostAu);
-    return systemFrameRadiusAu(systemFramingDistanceAu(rings[rings.length - 1]));
-  }
-
-  /** Apparent size on screen, as a fraction of the frame's half-height. */
-  function apparentFraction(innermostAu: number, outermostAu: number, glowScale = 1): number {
-    return haloRadiusAu(innermostAu, outermostAu, glowScale) / frameRadiusFor(outermostAu);
-  }
-
-  function apparentPixels(innermostAu: number, outermostAu: number): number {
-    return apparentFraction(innermostAu, outermostAu) * REFERENCE_VIEWPORT_HALF_HEIGHT_PX;
-  }
-
-  it('scales with the star for a compact system, where the star is already big enough', () => {
-    // A tight frame relative to the star, so the star's own multiple is what decides.
-    const marker = 0.02;
-    const tightFrame = 0.5;
-    expect(starGlowExtentAu(marker, tightFrame)).toBeCloseTo(marker * 3.2, 9);
-    expect(starGlowExtentAu(marker * 2, tightFrame)).toBeCloseTo(marker * 2 * 3.2, 9);
-  });
-
-  it('floors against the frame once the star would otherwise vanish into it', () => {
-    // A star sized against a close-in orbit, framed from far enough out to hold a wide system:
-    // the multiple of the star is nothing, so the frame decides instead.
-    const tinyStar = 0.001;
-    const wideFrame = 56;
-    expect(starGlowExtentAu(tinyStar, wideFrame)).toBeGreaterThan(tinyStar * 3.2 * 100);
-  });
-
-  it('keeps the Sun visible at the distance that frames the solar system', () => {
-    // The case that prompted this: the solar system spans a factor of a hundred from Mercury to
-    // Pluto, so a disc that stays clear of Mercury is about a pixel across once Pluto is in view.
-    expect(apparentPixels(0.387, 39.288)).toBeGreaterThan(4);
-  });
-
-  it('leaves the inner orbits clear of the halo', () => {
-    // The other half of the same trade. Venus and Earth have to stay legible as rings around the
-    // star, which bounds the halo from above just as visibility bounds it from below.
-    const halo = haloRadiusAu(0.387, 39.288);
-    const VENUS_AU = 0.723;
-    const EARTH_AU = 1;
-    expect(halo).toBeLessThan(VENUS_AU);
-    expect(halo).toBeLessThan(EARTH_AU);
-  });
-
-  it('cannot clear Mercury as well, and does not pretend to', () => {
-    // Mercury's orbit is 0.7% of the framed radius — about three pixels — so it is inside any
-    // halo big enough to see. Pinned so the trade is a decision rather than an oversight.
-    expect(haloRadiusAu(0.387, 39.288)).toBeGreaterThan(0.387);
-  });
-
-  it('holds the floor across every system scale the datasets contain', () => {
-    // A compact system's star is genuinely large relative to its own system and keeps the bigger
-    // halo; the floor is not there to equalise them, only to stop the wide ones disappearing.
-    for (const [innermost, outermost] of [
-      [0.387, 39.288],
-      [0.035, 0.204],
-      [0.01154, 0.06189],
-      [1.2, 12.4]
-    ]) {
-      expect(apparentPixels(innermost, outermost)).toBeGreaterThan(4);
-    }
-  });
-
-  it('does not blot out the system it sits in', () => {
-    for (const [innermost, outermost] of [
-      [0.387, 39.288],
-      [0.035, 0.204],
-      [0.01154, 0.06189]
-    ]) {
-      expect(apparentFraction(innermost, outermost)).toBeLessThan(0.2);
-    }
-  });
-
-  it('dims for a star drawn from a colour rather than a photograph, but never below the floor', () => {
-    // Above the floor the multiplier applies...
-    expect(starGlowExtentAu(1, 10, 0.6)).toBeLessThan(starGlowExtentAu(1, 10, 1));
-    // ...and at the floor it cannot dim a star into invisibility.
-    expect(starGlowExtentAu(0.001, 56, 0.6)).toBe(starGlowExtentAu(0.001, 56, 1));
-  });
-
-  it('falls back to the star alone when there is no frame to measure against', () => {
-    for (const frame of [0, -1, Number.NaN]) {
-      expect(starGlowExtentAu(0.2, frame)).toBeCloseTo(0.2 * 3.2, 9);
-    }
-  });
-});
-
 describe('the grid and the framing together', () => {
   /** What the scene actually composes: rings from the orbits, then a distance from the rings. */
   function fit(outermostOrbitAu: number, viewport?: SystemViewport): { ring: number; frame: number } {
@@ -278,54 +178,41 @@ describe('star and framing together', () => {
 
 describe('bodyMarkerRadiusAu', () => {
   const EARTH_RADIUS_KM = 6371;
-  const SOLAR_SPAN_AU = 30.07;
+  const KM_PER_AU = 149597870.7;
 
-  it('scales in proportion to the system span', () => {
+  it('draws a body at its true size', () => {
-    const wide = bodyMarkerRadiusAu(EARTH_RADIUS_KM, SOLAR_SPAN_AU);
+    expect(bodyMarkerRadiusAu(EARTH_RADIUS_KM)).toBeCloseTo(EARTH_RADIUS_KM / KM_PER_AU, 12);
-    const compact = bodyMarkerRadiusAu(EARTH_RADIUS_KM, SOLAR_SPAN_AU / 100);
+    expect(bodyMarkerRadiusAu(696340)).toBeCloseTo(0.00465, 5); // the Sun
-
-    expect(compact / wide).toBeCloseTo(0.01, 6);
   });
 
-  it('keeps a marker far smaller than the orbits it sits on, at any scale', () => {
+  it('keeps a moon smaller than its planet and outside it, which the exaggeration did not', () => {
-    // A fixed 0.09 AU marker inside Gl 357's 0.204 AU system was wider than the orbits, so one
+    // Jupiter and Ganymede both ran past the old 0.09 AU ceiling and came out one size, so
-    // planet swallowed the whole view.
+    // Ganymede orbited inside Jupiter; Phobos and Triton sat entirely within Mars and Neptune.
-    for (const span of [0.06, 0.204, 1, 30.07, 800]) {
+    const jupiter = bodyMarkerRadiusAu(69911);
-      expect(bodyMarkerRadiusAu(EARTH_RADIUS_KM, span)).toBeLessThan(span / 5);
+    const ganymede = bodyMarkerRadiusAu(2634);
-    }
+    const callisto = bodyMarkerRadiusAu(2410);
+    const GANYMEDE_SEMI_MAJOR_AXIS_AU = 0.007155;
+
+    expect(ganymede).toBeLessThan(jupiter);
+    expect(callisto).toBeLessThan(ganymede);
+    expect(jupiter + ganymede).toBeLessThan(GANYMEDE_SEMI_MAJOR_AXIS_AU);
   });
 
-  it('gives compact and wide systems the same apparent marker size', () => {
+  it('keeps Phobos outside Mars, where a marker scaled to the system buried it', () => {
-    const apparent = (span: number) => bodyMarkerRadiusAu(EARTH_RADIUS_KM, span) / systemFramingDistanceAu(span);
+    const PHOBOS_SEMI_MAJOR_AXIS_AU = 0.00006268;
 
-    expect(apparent(0.204)).toBeCloseTo(apparent(10), 6);
+    expect(bodyMarkerRadiusAu(3390) + bodyMarkerRadiusAu(11.27)).toBeLessThan(PHOBOS_SEMI_MAJOR_AXIS_AU);
   });
 
   it('still renders a bigger body as a bigger marker', () => {
-    const jupiter = bodyMarkerRadiusAu(69911, SOLAR_SPAN_AU);
+    expect(bodyMarkerRadiusAu(69911)).toBeGreaterThan(bodyMarkerRadiusAu(1188));
-    const pluto = bodyMarkerRadiusAu(1188, SOLAR_SPAN_AU);
-
-    expect(jupiter).toBeGreaterThan(pluto);
   });
 
-  it('falls back to the smallest marker for a body with no known radius', () => {
+  it('falls back to an Earth for a body with no published radius', () => {
-    const unknown = bodyMarkerRadiusAu(undefined, SOLAR_SPAN_AU);
+    for (const nothing of [undefined, 0, -1]) {
-    const pluto = bodyMarkerRadiusAu(1188, SOLAR_SPAN_AU);
+      expect(bodyMarkerRadiusAu(nothing as number | undefined)).toBeCloseTo(EARTH_RADIUS_KM / KM_PER_AU, 12);
-
-    expect(unknown).toBeGreaterThan(0);
-    expect(unknown).toBeLessThanOrEqual(pluto);
-  });
-
-  it('treats a missing span as the reference scale rather than collapsing to zero', () => {
-    for (const span of [0, -5, Number.NaN]) {
-      expect(bodyMarkerRadiusAu(EARTH_RADIUS_KM, span)).toBeGreaterThan(0);
     }
   });
-
-  it('leaves the solar system essentially as it was before scaling', () => {
-    // The constants were tuned at this span, so the scale factor here is ~1.
-    expect(bodyMarkerRadiusAu(EARTH_RADIUS_KM, SOLAR_SPAN_AU)).toBeCloseTo(0.09, 2);
-  });
 });
 
 describe('systemGridRingsAu', () => {

src/app/features/galaxy-system/system-framing.ts

@@ -27,31 +27,6 @@ export const DEFAULT_STAR_MARKER_RADIUS_AU = 0.2;
  */
 const STAR_RADIUS_TO_INNERMOST_ORBIT = 0.45;
 
-/**
- * Halo extent as a multiple of the star's own radius, and the floor on that extent as a
- * fraction of the framed radius.
- *
- * The floor is what keeps a star visible. A system's star is sized against its *innermost*
- * orbit — it must never swallow its closest planet — while the camera is placed to frame the
- * *outermost* ring, and those differ by a factor of a hundred in the solar system. At the
- * distance that fits Pluto in view, a disc that stays clear of Mercury is about one pixel
- * across; there is no radius that satisfies both, because the information genuinely does not
- * fit on one screen at that zoom.
- *
- * The halo resolves it, because light is not a surface: a glow that reaches past the innermost
- * orbit does not claim the star is that large, it claims the star is bright. So the disc stays
- * honest to the orbits and the halo is floored against the frame.
- *
- * The floor is set by what it must not cover. Its visual radius is half the extent, so a floor
- * of `f` puts the halo's edge at `f / 2` of the frame radius — and the orbits it has to leave
- * legible sit at their own fraction of that same radius. In the solar system, framed to hold
- * Pluto, Venus's orbit is at 1.3% of the frame radius and Earth's at 1.8%, so a floor of 2%
- * leaves both of them outside the halo. Mercury's, at 0.7%, is inside it — and would be at any
- * halo large enough to see, since the orbit itself is only a few pixels wide there.
- */
-const STAR_GLOW_TO_MARKER = 3.2;
-const MIN_STAR_GLOW_TO_FRAME = 0.02;
-
 /**
  * Clear space left around the framed radius, as a fraction of it. The camera backs off this
  * much further than the geometry strictly needs, so the outermost ring sits inside the frame
@@ -150,20 +125,6 @@ export function systemFrameRadiusAu(distanceAu: number, viewport: SystemViewport
   return distanceAu * tightHalfExtent(viewport);
 }
 
-/**
- * Extent (AU) of the star's glow sprite — how wide it is drawn, not its radius.
- *
- * Normally a multiple of the star's own radius, so a compact system keeps the corona it has.
- * Floored against the framed radius, so a star framed from far enough out to hold its whole
- * system still reads as a bright point rather than disappearing into it. `glowScale` lets a
- * caller dim the halo for stars drawn without a real photograph.
- */
-export function starGlowExtentAu(markerRadiusAu: number, frameRadiusAu: number, glowScale = 1): number {
-  const fromStar = markerRadiusAu * STAR_GLOW_TO_MARKER * glowScale;
-  const fromFrame = Number.isFinite(frameRadiusAu) && frameRadiusAu > 0 ? frameRadiusAu * MIN_STAR_GLOW_TO_FRAME : 0;
-  return Math.max(fromStar, fromFrame);
-}
-
 /**
  * Distance (AU) to settle the camera at so that `framedRadiusAu` fits in view with a margin
  * around it.
@@ -223,32 +184,35 @@ export function systemGridRingsAu(outermostOrbitAu: number): number[] {
 }
 
 /**
- * Span of the solar system, in AU, used as the reference every other system's marker sizes are
+ * A body is drawn at its true size. Astronomical Unit in kilometres, and what a body with neither
- * scaled against. The marker constants below were tuned by eye at this scale.
+ * a radius nor a mass to estimate one from is drawn as: an Earth, for want of anything better —
+ * exoplanets with a mass and no radius get an estimate from their mass before they reach here.
  */
-const REFERENCE_SYSTEM_SPAN_AU = 30;
+const KM_PER_AU = 149597870.7;
-
+const DEFAULT_BODY_RADIUS_KM = 6371;
-/** Exaggerated (non-physical) marker sizes at the reference scale, so planets stay visible. */
-const MIN_MARKER_RADIUS_AU = 0.012;
-const MAX_MARKER_RADIUS_AU = 0.09;
-/** Physical radius (km) that maps to one AU of marker radius before clamping. */
-const MARKER_RADIUS_KM_PER_AU = 18000;
 
 /**
- * Radius (AU) to draw a planet, moon or exoplanet marker at, scaled to the system it sits in.
+ * The Sun's own radius, in AU — the one star whose size this map knows.
  *
- * Marker sizes are deliberately exaggerated — a true-scale Earth would be invisible next to its
+ * Every other star is drawn at {@link starMarkerRadiusAu}, a size derived from its innermost
- * own orbit — but the exaggeration has to be relative to the system, not absolute. Fixed AU
+ * orbit rather than measured, because no stellar radius reaches the app: the catalogue carries
- * sizes tuned against the solar system's 30 AU span become grotesque in a system a hundredth
+ * positions, magnitudes and colours. Gaia publishes `radius_gspphot` for most of what is drawn
- * that size: a marker of 0.09 AU inside a 0.2 AU system is wider than the orbits it sits on, so
+ * here, and until the ETL fetches it, a system's star is the one body in the view that is not
- * a single planet swallows the entire view.
+ * to scale.
- *
- * Scaling by the span keeps every system looking like the solar system does: orbits legible,
- * planets as small dots on them.
  */
-export function bodyMarkerRadiusAu(radiusKm: number | undefined, systemSpanAu: number): number {
+export const SUN_RADIUS_AU = 696340 / KM_PER_AU;
-  const span = Number.isFinite(systemSpanAu) && systemSpanAu > 0 ? systemSpanAu : REFERENCE_SYSTEM_SPAN_AU;
-  const atReferenceScale = radiusKm ? clamp(radiusKm / MARKER_RADIUS_KM_PER_AU, MIN_MARKER_RADIUS_AU, MAX_MARKER_RADIUS_AU) : MIN_MARKER_RADIUS_AU;
 
-  return atReferenceScale * (span / REFERENCE_SYSTEM_SPAN_AU);
+/**
+ * Radius (AU) to draw a planet, moon or exoplanet marker at: its own, unexaggerated.
+ *
+ * Sizes used to be exaggerated and scaled to the system span, which is what made a moon the size
+ * of its planet — Jupiter and Ganymede both ran past the ceiling and were drawn at one radius, so
+ * every moon orbited inside its parent. True scale needs no rule to prevent that: physics already
+ * puts a moon outside the planet it orbits, and the Sun at a hundredth of Mercury’s orbit.
+ *
+ * What true scale costs is visibility at the framing that holds a whole system, where every body
+ * is sub-pixel. That is paid for on screen instead, in pixels, by the scene's `keepMarkersLegible`.
+ */
+export function bodyMarkerRadiusAu(radiusKm: number | undefined): number {
+  return (radiusKm && radiusKm > 0 ? radiusKm : DEFAULT_BODY_RADIUS_KM) / KM_PER_AU;
 }

src/app/features/galaxy-system/system-orbits-renderer.spec.ts

@@ -372,3 +372,95 @@ describe('SystemOrbitsRenderer exoplanet propagation', () => {
     });
   });
 });
+
+describe('rotation', () => {
+  /** Earth, near enough: a day of 23.934 h, tipped 23.44 degrees off its orbit. */
+  function spinning(overrides: Partial<BodyRecord> = {}): BodyRecord {
+    return {
+      id: 'earth',
+      systemStarId: 0,
+      name: 'Earth',
+      kind: 'planet',
+      radiusKm: 6371,
+      orbit: { semiMajorAxisAu: 1, eccentricity: 0.0167, inclinationDeg: 0, longitudeOfAscendingNodeDeg: 0, argumentOfPeriapsisDeg: 0, meanAnomalyAtEpochDeg: 0, epochJd: DEFAULT_EPOCH_JD },
+      rotationPeriodHours: 23.934,
+      obliquityDeg: 23.4392911,
+      ...overrides
+    };
+  }
+
+  /** How far the marker has turned about its own axis between two dates, in degrees. */
+  function turnedDegrees(body: BodyRecord, afterDays: number): number {
+    const renderer = new SystemOrbitsRenderer([body], [], undefined, 1);
+    renderer.update(DEFAULT_EPOCH_JD);
+    const start = renderer.members[0].marker.quaternion.clone();
+    renderer.update(DEFAULT_EPOCH_JD + afterDays);
+    const turn = start.invert().multiply(renderer.members[0].marker.quaternion);
+    const axis = new THREE.Vector3();
+    const angle = 2 * Math.acos(Math.min(1, Math.abs(turn.w)));
+    turn.normalize();
+    axis.set(turn.x, turn.y, turn.z);
+    const signed = axis.y >= 0 ? angle : -angle;
+    return (signed * 180) / Math.PI;
+  }
+
+  it('turns a body once per its own sidereal day', () => {
+    // A full turn in 23.934 h, so a quarter of that is a quarter turn.
+    expect(Math.abs(turnedDegrees(spinning(), 23.934 / 96))).toBeCloseTo(90, 1);
+  });
+
+  /**
+   * Which way a body spins in the world: its angular velocity projected on its orbit's normal.
+   * Positive is prograde, turning the same way it goes round; negative is retrograde.
+   */
+  function spinSense(body: BodyRecord): number {
+    const renderer = new SystemOrbitsRenderer([body], [], undefined, 1);
+    renderer.update(DEFAULT_EPOCH_JD);
+    const start = renderer.members[0].marker.quaternion.clone();
+    renderer.update(DEFAULT_EPOCH_JD + 0.01);
+    const turn = renderer.members[0].marker.quaternion.clone().multiply(start.invert());
+    const axis = new THREE.Vector3(turn.x, turn.y, turn.z).multiplyScalar(Math.sign(turn.w));
+    return axis.normalize().dot(new THREE.Vector3(0, 0, 1).applyQuaternion(renderer.referenceFrame));
+  }
+
+  it('turns Venus backwards, as Horizons gives it: a negative rate and an obliquity past 90', () => {
+    // Both say retrograde, in two conventions. Applied together they cancelled into a forward
+    // turn, which is how Venus and Uranus used to be drawn.
+    const venus = spinning({ id: 'venus', rotationPeriodHours: -5832.54, obliquityDeg: 177.3 });
+
+    expect(spinSense(spinning())).toBeGreaterThan(0.9);
+    expect(spinSense(venus)).toBeLessThan(-0.9);
+  });
+
+  it('reads the sign of the period only where no obliquity says which way the pole points', () => {
+    expect(spinSense(spinning({ rotationPeriodHours: -23.934, obliquityDeg: undefined }))).toBeLessThan(-0.9);
+    expect(spinSense(spinning({ rotationPeriodHours: 23.934, obliquityDeg: undefined }))).toBeGreaterThan(0.9);
+  });
+
+  it('leaves a body with no published rotation still', () => {
+    // Titan: Horizons states no period for it, and an invented one would be a claim.
+    const renderer = new SystemOrbitsRenderer([spinning({ rotationPeriodHours: undefined })], [], undefined, 1);
+    renderer.update(DEFAULT_EPOCH_JD);
+    const start = renderer.members[0].marker.quaternion.clone();
+    renderer.update(DEFAULT_EPOCH_JD + 40);
+
+    expect(renderer.members[0].marker.quaternion.angleTo(start)).toBe(0);
+  });
+});
+
+describe('exoplanet size without a measured radius', () => {
+  const radiusOf = (overrides: Partial<ExoplanetRecord>): number => {
+    const renderer = new SystemOrbitsRenderer([], [exoplanet(overrides)], undefined, 1);
+    return ((renderer.members[0].marker as THREE.Mesh).geometry as THREE.SphereGeometry).parameters.radius;
+  };
+  const EARTH_AU = 6371 / 149597870.7;
+
+  it('draws a giant known only by its mass at about Jupiter’s size, not at an Earth', () => {
+    // 14 Her b: 2 829 Earth masses, no radius. It used to come out the size of the Earth.
+    expect(radiusOf({ radiusEarth: undefined, massEarth: 2829 }) / EARTH_AU).toBeCloseTo(11.2, 1);
+  });
+
+  it('keeps a measured radius over any estimate', () => {
+    expect(radiusOf({ radiusEarth: 1.88, massEarth: 2829 }) / EARTH_AU).toBeCloseTo(1.88, 2);
+  });
+});

src/app/features/galaxy-system/system-orbits-renderer.ts

@@ -3,7 +3,8 @@ import * as THREE from 'three/webgpu';
 import { appearanceForBody, appearanceForExoplanet } from '../../shared/astro/body-appearance';
 import { gmForParent } from '../../shared/astro/constants';
 import { PlanetAppearance } from '../../shared/astro/planet-appearance';
-import { MARKER_TEXTURE_HEIGHT, MARKER_TEXTURE_WIDTH, planetTexture } from '../../shared/rendering/procedural-planet-texture';
+import { planetTexture } from '../../shared/rendering/procedural-planet-texture';
+import { bodyTexturePath, loadCachedTexture } from '../../shared/rendering/texture-catalog';
 import { isPropagatableOrbit, orbitEllipsePoints, propagateOrbit, resolveGravitationalParameter, resolveOrbitalElements } from '../../shared/astro/kepler';
 import { CartesianCoordinates, OBLIQUITY_J2000_DEG } from '../../shared/astro/coordinates';
 import { BodyRecord, OrbitalElements } from '../../shared/models/body.model';
@@ -18,6 +19,8 @@ export interface SystemMember {
   id: string;
   kind: SystemMemberKind;
   marker: THREE.Object3D;
+  /** For a moon, the id of the body it orbits: what its drawn size is held against. */
+  parentId?: string;
 }
 
 const PLANET_COLOR = new THREE.Color(0.55, 0.75, 1.0);
@@ -119,21 +122,110 @@ function buildOrbitLine(elements: OrbitalElements, kind: SystemMemberKind, frame
 }
 
 /**
- * A marker sphere, surfaced with the body's own derived appearance rather than a flat category
+ * A marker sphere, surfaced with the body's own photograph where one has ever been taken, and
- * colour — so a system reads as a set of distinct worlds at a glance, and the colour of each is
+ * with a texture derived from its measurements where none has — and lit by its star either way,
- * a consequence of its measurements rather than of which list it came from.
+ * so a world shows the day and night it actually has.
  *
- * The texture is tiny (see `MARKER_TEXTURE_WIDTH`): a marker is a few pixels across, so what
+ * The photographs were already in the repository, used only by the detail page: the system view
- * survives is essentially its average colour, and generating it costs well under a millisecond.
+ * drew every body from a 32 by 16 pixel procedural texture instead, which at a few pixels across
+ * was indistinguishable from its average colour and, once the camera closed in, was a blur. A
+ * marker can now fill the frame, so it takes the real image at the size the detail page uses.
  */
-function buildMarker(kind: SystemMemberKind, radiusKm: number | undefined, systemSpanAu: number, appearance: PlanetAppearance | undefined): THREE.Mesh {
+function buildMarker(id: string | undefined, kind: SystemMemberKind, radiusKm: number | undefined, appearance: PlanetAppearance | undefined): THREE.Mesh {
-  const geometry = new THREE.SphereGeometry(bodyMarkerRadiusAu(radiusKm, systemSpanAu), 16, 12);
+  const geometry = new THREE.SphereGeometry(bodyMarkerRadiusAu(radiusKm), MARKER_WIDTH_SEGMENTS, MARKER_HEIGHT_SEGMENTS);
-  const material = appearance
+  const photograph = id ? bodyTexturePath(id) : undefined;
-    ? new THREE.MeshBasicMaterial({ map: planetTexture(appearance, { width: MARKER_TEXTURE_WIDTH, height: MARKER_TEXTURE_HEIGHT }) })
+  // 128 by 64 for the derived texture, not the detail page's 512 by 256: that size costs about
-    : new THREE.MeshBasicMaterial({ color: colorForKind(kind) });
+  // 60 ms a body on the main thread, 360 ms on entering a six-planet system, for a disc that is a
+  // few pixels across until the camera is on top of it.
+  const map = photograph ? loadCachedTexture(photograph) : appearance ? planetTexture(appearance, { width: 128, height: 64 }) : undefined;
+  const material = new THREE.MeshStandardMaterial({
+    map,
+    color: map ? 0xffffff : colorForKind(kind),
+    roughness: 1,
+    metalness: 0
+  });
   return new THREE.Mesh(geometry, material);
 }
 
+/**
+ * The star's own light, at the centre of the system it lights.
+ *
+ * `decay` is 0, which is not what light does: a point source falls off with the square of the
+ * distance, and under that law Neptune, at 30.2 AU, receives about a six-thousandth of what
+ * Mercury does at 0.39 AU and reads as black. The map is a set of worlds to look at rather than a
+ * light meter, so each is lit as a photograph of it would be — the same concession the pixel
+ * floor makes for size. What the light does carry truthfully is which side is day: every body
+ * shows its lit face toward the star, and the terminator falls where it really falls.
+ *
+ * White, at π: a Lambertian surface returns intensity / π of its texture where the light falls
+ * square on it, so π gives back the photograph itself at the point facing the star, and less
+ * towards the limb. A warm tint or a smaller figure darkened the photographs below what they are.
+ */
+function starLight(): THREE.PointLight {
+  const light = new THREE.PointLight(0xffffff, Math.PI, 0, 0);
+  light.position.set(0, 0, 0);
+  return light;
+}
+
+/**
+ * Sphere segments. On a UV sphere the silhouette seen down the pole is the ring of width segments
+ * and the one seen from the side is the meridian profile, so height at half the width makes the
+ * error the same from every direction: at 64 by 32 a body filling the screen — Jupiter reaches
+ * 641 px of radius in the plan view — strays under a pixel from its true circle.
+ */
+const MARKER_WIDTH_SEGMENTS = 64;
+const MARKER_HEIGHT_SEGMENTS = 32;
+
+/**
+ * A drawn radius, in Earth radii, for an exoplanet that has a mass and no measured radius — 1 076
+ * of the 1 692 drawn, most of them found by radial velocity, and most of those giants: their
+ * median is 315 Earth masses. Drawn at an Earth, as they were, a nine-Jupiter-mass planet came out
+ * smaller than its system's super-Earth.
+ *
+ * A rough power law, capped at Jupiter's radius: giants from a third of a Jupiter mass to ten are
+ * all about Jupiter's size, since past that point added mass compresses rather than inflates. It
+ * sets a size to draw, not a figure to print — the readout still says the radius is unknown.
+ */
+function radiusFromMassEarth(massEarth: number | null | undefined): number | undefined {
+  return massEarth && massEarth > 0 ? Math.min(JUPITER_RADIUS_EARTH, massEarth ** 0.55) : undefined;
+}
+const JUPITER_RADIUS_EARTH = 11.2;
+
+/** Local axis a sphere is built around, and what the spin is applied about. */
+const SPIN_AXIS = new THREE.Vector3(0, 1, 0);
+const HOURS_PER_DAY = 24;
+
+/**
+ * How a body is turned at a given date: its own sidereal rotation, about its own axis.
+ *
+ * The obliquity fixes how far the pole leans from the orbit normal, and nothing more: which way
+ * it leans needs the pole's right ascension, which the Horizons pages this reads do not carry. The
+ * lean is taken about the orbit's ascending node because that is the one line the elements name,
+ * not because the data says so — so the tilt is real and its azimuth is not. Likewise the phase:
+ * each body starts at its elements' epoch (2025-01-01 here) in an arbitrary orientation, the
+ * shortest rotation of +Y onto its axis, and turns from there. The rate and the sense are real;
+ * the face towards the camera is not.
+ *
+ * Horizons states a retrograde spin twice over, in two conventions: an obliquity past 90 degrees
+ * (Venus 177.3, Uranus 97.8) and a negative rate. Either one alone turns the body backwards, and
+ * both together cancel into a forward turn — which is how Venus and Uranus were drawn. Where an
+ * obliquity is given it carries the sense, and the period is taken as a magnitude; the sign of the
+ * period is only read for a body with no obliquity at all.
+ */
+function spinFor(elements: OrbitalElements, frame: THREE.Quaternion, rotationPeriodHours: number, obliquityDeg: number | undefined, epochJd: number): THREE.Quaternion {
+  const node = elements.longitudeOfAscendingNodeDeg * DEG_TO_RAD;
+  const inclination = elements.inclinationDeg * DEG_TO_RAD;
+  const nodeDirection = new THREE.Vector3(Math.cos(node), Math.sin(node), 0);
+  const axis = new THREE.Vector3(Math.sin(inclination) * Math.sin(node), -Math.sin(inclination) * Math.cos(node), Math.cos(inclination))
+    .applyAxisAngle(nodeDirection, (obliquityDeg ?? 0) * DEG_TO_RAD)
+    .applyQuaternion(frame);
+  const period = obliquityDeg === undefined ? rotationPeriodHours : Math.abs(rotationPeriodHours);
+  const turns = ((epochJd - elements.epochJd) * HOURS_PER_DAY) / period;
+  return new THREE.Quaternion()
+    .setFromUnitVectors(SPIN_AXIS, axis)
+    .multiply(new THREE.Quaternion().setFromAxisAngle(SPIN_AXIS, turns * 2 * Math.PI));
+}
+
 interface TrackedTopLevelBody {
   id: string;
   kind: SystemMemberKind;
@@ -144,6 +236,9 @@ interface TrackedTopLevelBody {
   frame: THREE.Quaternion;
   /** AU position last computed for this body; moons read their parent's here. */
   position: THREE.Vector3;
+  /** Sidereal rotation, where the catalogue publishes one; negative is retrograde. */
+  rotationPeriodHours?: number;
+  obliquityDeg?: number;
 }
 
 interface TrackedMoon {
@@ -154,6 +249,8 @@ interface TrackedMoon {
   frame: THREE.Quaternion;
   pivot: THREE.Group;
   parentId: string;
+  rotationPeriodHours?: number;
+  obliquityDeg?: number;
 }
 
 /**
@@ -206,8 +303,6 @@ export class SystemOrbitsRenderer {
     const members: SystemMember[] = [];
     const topLevelBodiesById = new Map<string, BodyRecord>();
 
-    // Measured before anything is built, because marker sizes are scaled against the span and
-    // the markers are created as the bodies are added.
     const topLevelAxes = [
       ...bodies.filter((body) => !body.parentBodyId).map((body) => body.orbit.semiMajorAxisAu),
       ...exoplanets.filter((exoplanet) => isPropagatableOrbit(exoplanet.orbit)).map((exoplanet) => exoplanet.orbit.semiMajorAxisAu!)
@@ -227,7 +322,7 @@ export class SystemOrbitsRenderer {
       }
       // A body reaches here only when it has no parentBodyId, so `kind` is 'planet' or 'dwarf'.
       const kind: SystemMemberKind = body.kind;
-      const tracked = this.addTopLevelBody(body.id, kind, body.orbit, gmForParent(undefined), body.radiusKm, ECLIPTIC_FRAME, appearanceForBody(body, bodies, hostLuminositySolar));
+      const tracked = this.addTopLevelBody(body.id, kind, body.orbit, gmForParent(undefined), body.radiusKm, ECLIPTIC_FRAME, appearanceForBody(body, bodies, hostLuminositySolar), { periodHours: body.rotationPeriodHours, obliquityDeg: body.obliquityDeg });
       members.push({ id: body.id, kind, marker: tracked.marker });
     }
 
@@ -240,8 +335,8 @@ export class SystemOrbitsRenderer {
       if (!parentTracked) {
         continue; // orphaned moon reference; skip rather than crash.
       }
-      const moon = this.addMoon(body.id, body.orbit, gmForParent(body.parentBodyId), body.radiusKm, parentTracked, ECLIPTIC_FRAME, appearanceForBody(body, bodies, hostLuminositySolar));
+      const moon = this.addMoon(body.id, body.orbit, gmForParent(body.parentBodyId), body.radiusKm, parentTracked, ECLIPTIC_FRAME, appearanceForBody(body, bodies, hostLuminositySolar), { periodHours: body.rotationPeriodHours, obliquityDeg: body.obliquityDeg });
-      members.push({ id: body.id, kind: 'moon', marker: moon.marker });
+      members.push({ id: body.id, kind: 'moon', marker: moon.marker, parentId: parent.id });
     }
 
     // Every exoplanet in a system shares the same line of sight, so the frame is built once.
@@ -256,7 +351,8 @@ export class SystemOrbitsRenderer {
         continue;
       }
       const elements = resolveOrbitalElements(exoplanet.orbit);
-      const radiusKm = exoplanet.radiusEarth ? exoplanet.radiusEarth * EARTH_RADIUS_KM : undefined;
+      const radiusEarth = exoplanet.radiusEarth ?? radiusFromMassEarth(exoplanet.massEarth);
+      const radiusKm = radiusEarth ? radiusEarth * EARTH_RADIUS_KM : undefined;
       // Not `gmForParent(undefined)`: that assumes a solar-mass host for every system, and
       // most exoplanet hosts are red dwarfs a fraction of the Sun's mass.
       const gm = resolveGravitationalParameter({
@@ -299,6 +395,9 @@ export class SystemOrbitsRenderer {
 
       this.object.add(this.grid.object, this.tethers.object);
     }
+    // The star lights its own system. The star marker itself is unlit — it is the source, not a
+    // surface — so nothing here changes how it is drawn.
+    this.object.add(starLight());
   }
 
   /** Recomputes every marker's position for the given Julian date. Call once per tick. */
@@ -307,6 +406,9 @@ export class SystemOrbitsRenderer {
       const orbital = propagateOrbit(body.elements, body.gmAu3PerDay2, epochJd);
       body.position.set(orbital.x, orbital.y, orbital.z).applyQuaternion(body.frame);
       body.marker.position.copy(body.position);
+      if (body.rotationPeriodHours) {
+        body.marker.quaternion.copy(spinFor(body.elements, body.frame, body.rotationPeriodHours, body.obliquityDeg, epochJd));
+      }
     }
 
     for (const moon of this.moons) {
@@ -317,6 +419,9 @@ export class SystemOrbitsRenderer {
       moon.pivot.position.copy(parent.position);
       const orbital = propagateOrbit(moon.elements, moon.gmAu3PerDay2, epochJd);
       moon.marker.position.set(orbital.x, orbital.y, orbital.z).applyQuaternion(moon.frame);
+      if (moon.rotationPeriodHours) {
+        moon.marker.quaternion.copy(spinFor(moon.elements, moon.frame, moon.rotationPeriodHours, moon.obliquityDeg, epochJd));
+      }
     }
 
     // Moons are left out: their tether would land within a marker's width of their planet's and
@@ -371,15 +476,16 @@ export class SystemOrbitsRenderer {
     gmAu3PerDay2: number,
     radiusKm: number | undefined,
     frame: THREE.Quaternion,
-    appearance?: PlanetAppearance
+    appearance?: PlanetAppearance,
+    rotation?: { periodHours?: number; obliquityDeg?: number }
   ): TrackedTopLevelBody {
     const orbitLine = buildOrbitLine(elements, kind, frame);
-    const marker = buildMarker(kind, radiusKm, this.maxTopLevelSemiMajorAxisAu, appearance);
+    const marker = buildMarker(id, kind, radiusKm, appearance);
     this.object.add(orbitLine, marker);
     this.trackDisposable(orbitLine.geometry, orbitLine.material as THREE.Material);
     this.trackDisposable(marker.geometry, marker.material as THREE.Material);
 
-    const tracked: TrackedTopLevelBody = { id, kind, elements, gmAu3PerDay2, marker, frame, position: new THREE.Vector3() };
+    const tracked: TrackedTopLevelBody = { id, kind, elements, gmAu3PerDay2, marker, frame, position: new THREE.Vector3(), rotationPeriodHours: rotation?.periodHours, obliquityDeg: rotation?.obliquityDeg };
     this.topLevelBodies.push(tracked);
     return tracked;
   }
@@ -391,17 +497,18 @@ export class SystemOrbitsRenderer {
     radiusKm: number | undefined,
     parent: TrackedTopLevelBody,
     frame: THREE.Quaternion,
-    appearance?: PlanetAppearance
+    appearance?: PlanetAppearance,
+    rotation?: { periodHours?: number; obliquityDeg?: number }
   ): TrackedMoon {
     const pivot = new THREE.Group();
     const orbitLine = buildOrbitLine(elements, 'moon', frame);
-    const marker = buildMarker('moon', radiusKm, this.maxTopLevelSemiMajorAxisAu, appearance);
+    const marker = buildMarker(id, 'moon', radiusKm, appearance);
     pivot.add(orbitLine, marker);
     this.object.add(pivot);
     this.trackDisposable(orbitLine.geometry, orbitLine.material as THREE.Material);
     this.trackDisposable(marker.geometry, marker.material as THREE.Material);
 
-    const moon: TrackedMoon = { id, elements, gmAu3PerDay2, marker, frame, pivot, parentId: parent.id };
+    const moon: TrackedMoon = { id, elements, gmAu3PerDay2, marker, frame, pivot, parentId: parent.id, rotationPeriodHours: rotation?.periodHours, obliquityDeg: rotation?.obliquityDeg };
     this.moons.push(moon);
     return moon;
   }

src/app/features/hud/hud-dock.component.spec.ts

@@ -252,4 +252,118 @@ describe('HudDockComponent', () => {
     fixture.detectChanges();
     expect(tab('Readout').getAttribute('aria-selected')).toBe('true');
   });
+
+  it('will not plot from a departure that was typed but never chosen', () => {
+    setReadout();
+    fixture.componentRef.setInput('routing', true);
+    fixture.componentRef.setInput('currentStar', { id: 3, name: "Barnard's Star", subtitle: '1.8 pc' });
+    fixture.componentRef.setInput('routeOptions', [{ id: 7, name: 'Sirius', subtitle: '2.6 pc' }]);
+    fixture.componentRef.setInput('defaultTab', 'routes');
+    fixture.detectChanges();
+    const plot = () => [...host().querySelectorAll<HTMLButtonElement>('button')].find((button) => button.textContent?.includes('Plot route'))!;
+    const type = (field: string, value: string) => {
+      const input = host().querySelector<HTMLInputElement>(`#route-${field}`)!;
+      input.value = value;
+      input.dispatchEvent(new Event('input'));
+      fixture.detectChanges();
+    };
+
+    type('to', 'Sir');
+    host().querySelector<HTMLButtonElement>('#dock-panel-routes ul button')!.click();
+    fixture.detectChanges();
+    // With the departure field empty, the view's own star stands in for it.
+    expect(plot().disabled).toBe(false);
+
+    // Text that names no chosen star is not a departure: plotting from the view's star instead
+    // would name one place and leave from another.
+    type('from', 'Sol');
+    expect(plot().disabled).toBe(true);
+
+    type('from', '');
+    expect(plot().disabled).toBe(false);
+
+    // A space is not text that names a star: the field looks empty, the scene offers nothing to
+    // choose for it, and the button going dead would have nothing on screen to explain it.
+    type('from', ' ');
+    expect(plot().disabled).toBe(false);
+
+    // The offer beside a refusal is the same request by another route, so it is held to the same
+    // test: moving the range with nothing to plot leaves the panel contradicting itself.
+    fixture.componentRef.setInput('routeResult', { stars: [], totalPc: 0, neededRangePc: 1.8, gaveUp: false, least: true });
+    fixture.detectChanges();
+    const offer = () => host().querySelector<HTMLButtonElement>('[data-testid="route-summary"] button')!;
+    expect(offer().disabled).toBe(false);
+
+    type('from', 'Sol');
+    expect(offer().disabled).toBe(true);
+  });
+
+  it('does not replay the acquire wipe over the Routes panel, whose entries survive the trip', () => {
+    setReadout();
+    fixture.componentRef.setInput('routing', true);
+    fixture.componentRef.setInput('display', DEFAULT_HUD_DISPLAY);
+    fixture.componentRef.setInput('defaultTab', 'routes');
+    fixture.detectChanges();
+
+    // The wipe clips its panel for 380 ms, which swallows clicks on entries that are already there.
+    expect(host().querySelector('#dock-panel-routes')?.classList.contains('hud-acquire')).toBe(false);
+    tab('Display').click();
+    fixture.detectChanges();
+    expect(host().querySelector('#dock-panel-display')?.classList.contains('hud-acquire')).toBe(true);
+  });
+
+  it('says the search gave up rather than that there is no route, when that is what happened', () => {
+    fixture.componentRef.setInput('routing', true);
+    fixture.componentRef.setInput('defaultTab', 'routes');
+    const summary = () => host().querySelector('[data-testid="route-summary"]')?.textContent?.replace(/\s+/g, ' ').trim() ?? '';
+
+    fixture.componentRef.setInput('routeResult', { stars: [], totalPc: 0, neededRangePc: null, gaveUp: true, least: false });
+    fixture.detectChanges();
+    expect(summary()).toBe('Too many stars to search at this range.');
+
+    // Having looked everywhere the range reaches is a different answer, and one that can be stated.
+    fixture.componentRef.setInput('routeResult', { stars: [], totalPc: 0, neededRangePc: null, gaveUp: false, least: true });
+    fixture.detectChanges();
+    expect(summary()).toContain('No chain of jumps up to');
+
+    // A range a chain was found at is worth offering — but the search that gave up at the range
+    // asked for still gave up, and saying "no route" beside the offer is saying it did not.
+    fixture.componentRef.setInput('routeResult', { stars: [], totalPc: 0, neededRangePc: 6.4, gaveUp: true, least: false });
+    fixture.detectChanges();
+    expect(summary()).toBe('Too many stars to search at this range. 6.40 pc would reach.');
+
+    // The other way round: the range asked for was searched to exhaustion and the wider search was
+    // the one that gave up. There is no route at this range, and nothing further can be claimed.
+    fixture.componentRef.setInput('routeResult', { stars: [], totalPc: 0, neededRangePc: null, gaveUp: false, least: false });
+    fixture.detectChanges();
+    expect(summary()).toBe('No route at this range.');
+  });
+
+  it('keeps what the Routes panel was set to across a trip to another tab', () => {
+    setReadout();
+    fixture.componentRef.setInput('routing', true);
+    fixture.componentRef.setInput('routeOptions', [{ id: 7, name: 'Sirius', subtitle: '2.6 pc' }]);
+    fixture.componentRef.setInput('defaultTab', 'routes');
+    fixture.detectChanges();
+
+    const destination = host().querySelector<HTMLInputElement>('#route-to')!;
+    destination.value = 'Sir';
+    destination.dispatchEvent(new Event('input'));
+    fixture.detectChanges();
+    host().querySelector<HTMLButtonElement>('#dock-panel-routes ul button')!.click();
+    const range = host().querySelector<HTMLInputElement>('#route-range')!;
+    range.value = '6';
+    range.dispatchEvent(new Event('input'));
+    fixture.detectChanges();
+
+    tab('Readout').click();
+    fixture.detectChanges();
+    expect(host().querySelector<HTMLElement>('#dock-panel-routes')!.hidden).toBe(true);
+    tab('Routes').click();
+    fixture.detectChanges();
+
+    expect(host().querySelector<HTMLElement>('#dock-panel-routes')!.hidden).toBe(false);
+    expect(host().querySelector<HTMLInputElement>('#route-to')!.value).toBe('Sirius');
+    expect(host().querySelector<HTMLInputElement>('#route-range')!.value).toBe('6');
+  });
 });

src/app/features/hud/hud-dock.component.ts

@@ -1,9 +1,27 @@
-import { ChangeDetectionStrategy, Component, computed, ElementRef, HostListener, inject, input, OnInit, output, signal, viewChild } from '@angular/core';
+import {
+  ChangeDetectionStrategy,
+  Component,
+  computed,
+  ElementRef,
+  HostListener,
+  inject,
+  input,
+  OnInit,
+  output,
+  signal,
+  viewChild,
+} from '@angular/core';
 
 import { Bookmark, BookmarksStore } from '../../shared/state/bookmarks.store';
+import { TIME_RATES, TimeStore } from '../../shared/state/time.store';
 import { BookmarkIconComponent } from '../../shared/ui/bookmark-icon.component';
 import { SearchComponent } from '../search/search.component';
-import { RouteRequest, RouteResult, RoutesPanelComponent, RouteStarOption } from './routes-panel.component';
+import {
+  RouteRequest,
+  RouteResult,
+  RoutesPanelComponent,
+  RouteStarOption,
+} from './routes-panel.component';
 
 export interface HudReadout {
   readonly label: string;
@@ -31,7 +49,16 @@ export interface HudDisplay {
   readonly plan: boolean;
 }
 
-export const DEFAULT_HUD_DISPLAY: HudDisplay = { labels: true, orbits: true, grid: true, deepSky: true, sky: true, systems: true, jumpLinks: false, plan: false };
+export const DEFAULT_HUD_DISPLAY: HudDisplay = {
+  labels: true,
+  orbits: true,
+  grid: true,
+  deepSky: true,
+  sky: true,
+  systems: true,
+  jumpLinks: false,
+  plan: false,
+};
 
 const DISPLAY_LAYERS: readonly { key: keyof HudDisplay; label: string }[] = [
   { key: 'labels', label: 'Labels' },
@@ -41,17 +68,26 @@ const DISPLAY_LAYERS: readonly { key: keyof HudDisplay; label: string }[] = [
   { key: 'sky', label: 'Sky' },
   { key: 'systems', label: 'Systems' },
   { key: 'jumpLinks', label: 'Jump links' },
-  { key: 'plan', label: 'Plan view' }
+  { key: 'plan', label: 'Plan view' },
 ];
 
 export type DockTab = 'search' | 'readout' | 'routes' | 'bookmarks' | 'display';
 
-const TAB_LABELS: Record<DockTab, string> = { search: 'Search', readout: 'Readout', routes: 'Routes', bookmarks: 'Bookmarks', display: 'Display' };
+const TAB_LABELS: Record<DockTab, string> = {
+  search: 'Search',
+  readout: 'Readout',
+  routes: 'Routes',
+  bookmarks: 'Bookmarks',
+  display: 'Display',
+};
 
 /** Tailwind's `sm` breakpoint: below it the dock is a bare tab strip and its panel is a sheet. */
 const WIDE_VIEWPORT = '(min-width: 640px)';
 /** One live query, read on every pointer-down, rather than a new MediaQueryList per read. */
-const wideViewportQuery = typeof window !== 'undefined' && typeof window.matchMedia === 'function' ? window.matchMedia(WIDE_VIEWPORT) : null;
+const wideViewportQuery =
+  typeof window !== 'undefined' && typeof window.matchMedia === 'function'
+    ? window.matchMedia(WIDE_VIEWPORT)
+    : null;
 
 function isWideViewport(): boolean {
   return wideViewportQuery?.matches ?? true;
@@ -74,7 +110,10 @@ function isWideViewport(): boolean {
   selector: 'app-hud-dock',
   changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [BookmarkIconComponent, RoutesPanelComponent, SearchComponent],
-  host: { class: 'pointer-events-none fixed inset-x-2 bottom-2 z-20 block font-body sm:inset-x-6 sm:bottom-6' },
+  host: {
+    class:
+      'pointer-events-none fixed inset-x-2 bottom-2 z-20 block font-body sm:inset-x-6 sm:bottom-6',
+  },
   template: `
     <!-- The column is transparent to the pointer and each surface in it opts back in: it is as
          wide as the strip and as tall as the open panel, so a solid one would swallow every
@@ -85,28 +124,54 @@ function isWideViewport(): boolean {
              locking on, once per switch, never per keystroke. -->
         @switch (tab) {
           @case ('search') {
-            <section id="dock-panel-search" role="tabpanel" aria-labelledby="dock-tab-search" class="hud-acquire pointer-events-auto mb-2 w-full max-w-xl">
+            <section
+              id="dock-panel-search"
+              role="tabpanel"
+              aria-labelledby="dock-tab-search"
+              class="hud-acquire pointer-events-auto mb-2 w-full max-w-xl"
+            >
               <app-search (picked)="onPicked()" />
             </section>
           }
           @case ('readout') {
-            <section id="dock-panel-readout" role="tabpanel" aria-labelledby="dock-tab-readout" class="hud-acquire hud-brackets hud-surface pointer-events-auto mb-2 w-full max-w-lg px-4 py-3">
+            <section
+              id="dock-panel-readout"
+              role="tabpanel"
+              aria-labelledby="dock-tab-readout"
+              class="hud-acquire hud-brackets hud-surface pointer-events-auto mb-2 w-full max-w-lg px-4 py-3"
+            >
               <p class="type-label text-muted">{{ eyebrow() }}</p>
               <div class="mt-1 flex items-start gap-2">
-                <p data-testid="hud-title" class="min-w-0 flex-1 text-lg font-bold tracking-[0.04em] text-text uppercase">{{ title() }}</p>
+                <p
+                  data-testid="hud-title"
+                  class="min-w-0 flex-1 text-lg font-bold tracking-[0.04em] text-text uppercase"
+                >
+                  {{ title() }}
+                </p>
                 <!-- Against null, not against falsiness: the Sun's catalogue id is 0, and a
                      truthiness test is what would quietly make the Solar System the one
                      system nobody could keep. -->
                 @if (keepableStarId() !== null) {
                   <button
                     type="button"
-          [attr.aria-label]="(bookmarks.has('star', keepableStarId()!) ? 'Forget ' : 'Keep ') + title()"
+                    [attr.aria-label]="
+                      (bookmarks.has('star', keepableStarId()!) ? 'Forget ' : 'Keep ') + title()
+                    "
                     [attr.aria-pressed]="bookmarks.has('star', keepableStarId()!)"
-          (click)="bookmarks.toggle({ kind: 'star', id: keepableStarId()!, name: title() })"
+                    (click)="
+                      bookmarks.toggle({ kind: 'star', id: keepableStarId()!, name: title() })
+                    "
                     class="shrink-0 p-1 transition-colors focus-visible:outline-1 focus-visible:-outline-offset-1 focus-visible:outline-accent"
-          [class]="bookmarks.has('star', keepableStarId()!) ? 'text-accent' : 'text-muted hover:text-accent'"
+                    [class]="
+                      bookmarks.has('star', keepableStarId()!)
+                        ? 'text-accent'
+                        : 'text-muted hover:text-accent'
+                    "
                   >
-          <app-bookmark-icon class="h-3.5 w-3.5" [kept]="bookmarks.has('star', keepableStarId()!)" />
+                    <app-bookmark-icon
+                      class="h-3.5 w-3.5"
+                      [kept]="bookmarks.has('star', keepableStarId()!)"
+                    />
                   </button>
                 }
               </div>
@@ -117,43 +182,54 @@ function isWideViewport(): boolean {
                 <dl class="mt-3 flex flex-wrap gap-x-6 gap-y-1">
                   @for (readout of readouts(); track readout.label) {
                     <div>
-                      <dt class="type-label text-muted">{{ readout.label }}@if (readout.derived) {<span class="text-accent/80" aria-hidden="true">*</span>}</dt>
+                      <dt class="type-label text-muted">
+                        {{ readout.label }}
+                        @if (readout.derived) {
+                          <span class="text-accent/80" aria-hidden="true">*</span>
+                        }
+                      </dt>
                       <dd class="mt-0.5 text-sm text-text tabular-nums">{{ readout.value }}</dd>
                     </div>
                   }
                 </dl>
               }
               @if (note() || hasDerived()) {
-                <p class="mt-3 border-t border-border/40 pt-2 text-[10px] leading-relaxed text-muted">@if (hasDerived()) {<span class="text-accent/80">*</span> Derived, not catalogued. }{{ note() }}</p>
+                <p
+                  class="mt-3 border-t border-border/40 pt-2 text-[10px] leading-relaxed text-muted"
+                >
+                  @if (hasDerived()) {
+                    <span class="text-accent/80">*</span> Derived, not catalogued.
                   }
-            </section>
+                  {{ note() }}
+                </p>
               }
-          @case ('routes') {
-            <section id="dock-panel-routes" role="tabpanel" aria-labelledby="dock-tab-routes" class="hud-acquire hud-brackets hud-surface pointer-events-auto mb-2 w-full max-w-xl px-4 py-3">
-              <app-routes-panel
-                [result]="routeResult()"
-                [options]="routeOptions()"
-                [currentStar]="currentStar()"
-                (queryChange)="routeQuery.emit($event)"
-                (routeRequested)="routeRequested.emit($event)"
-                (starSelected)="onRouteStarSelected($event)"
-                (rangeChange)="jumpRangeChange.emit($event)"
-              />
             </section>
           }
           @case ('bookmarks') {
-            <section id="dock-panel-bookmarks" role="tabpanel" aria-labelledby="dock-tab-bookmarks" class="hud-acquire hud-brackets hud-surface pointer-events-auto mb-2 w-full max-w-lg">
+            <section
+              id="dock-panel-bookmarks"
+              role="tabpanel"
+              aria-labelledby="dock-tab-bookmarks"
+              class="hud-acquire hud-brackets hud-surface pointer-events-auto mb-2 w-full max-w-lg"
+            >
               @if (bookmarks.bookmarks().length) {
                 <ul class="max-h-64 divide-y divide-border/25 overflow-y-auto">
-                  @for (bookmark of bookmarks.bookmarks(); track bookmark.kind + ':' + bookmark.id) {
+                  @for (
+                    bookmark of bookmarks.bookmarks();
+                    track bookmark.kind + ':' + bookmark.id
+                  ) {
                     <li class="flex items-stretch">
                       <button
                         type="button"
                         (click)="onBookmarkChosen(bookmark)"
                         class="flex min-w-0 flex-1 items-baseline gap-3 px-3 py-2 text-left transition-colors hover:bg-accent/8 focus-visible:bg-accent/12 focus-visible:outline-1 focus-visible:-outline-offset-1 focus-visible:outline-accent"
                       >
-                        <span class="min-w-0 flex-1 truncate text-sm text-text">{{ bookmark.name }}</span>
+                        <span class="min-w-0 flex-1 truncate text-sm text-text">{{
-                        <span class="type-label shrink-0 text-muted">{{ bookmark.kind === 'star' ? 'System' : 'Body' }}</span>
+                          bookmark.name
+                        }}</span>
+                        <span class="type-label shrink-0 text-muted">{{
+                          bookmark.kind === 'star' ? 'System' : 'Body'
+                        }}</span>
                       </button>
                       <button
                         type="button"
@@ -161,7 +237,15 @@ function isWideViewport(): boolean {
                         (click)="bookmarks.remove(bookmark.kind, bookmark.id)"
                         class="shrink-0 border-l border-border/25 px-3 text-muted transition-colors hover:bg-accent/8 hover:text-accent focus-visible:text-accent focus-visible:outline-1 focus-visible:-outline-offset-1 focus-visible:outline-accent"
                       >
-                        <svg class="h-3 w-3" viewBox="0 0 14 14" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" aria-hidden="true">
+                        <svg
+                          class="h-3 w-3"
+                          viewBox="0 0 14 14"
+                          fill="none"
+                          stroke="currentColor"
+                          stroke-width="1.5"
+                          stroke-linecap="round"
+                          aria-hidden="true"
+                        >
                           <path d="M3 3l8 8M11 3l-8 8" />
                         </svg>
                       </button>
@@ -170,13 +254,20 @@ function isWideViewport(): boolean {
                 </ul>
               } @else {
                 <p class="px-3 py-3 text-sm text-muted">
-                  Nothing kept yet. The <app-bookmark-icon class="inline-block h-3.5 w-3.5 -mb-0.5 text-accent" /> on a readout or a body keeps it here, in this browser.
+                  Nothing kept yet. The
+                  <app-bookmark-icon class="inline-block h-3.5 w-3.5 -mb-0.5 text-accent" /> on a
+                  readout or a body keeps it here, in this browser.
                 </p>
               }
             </section>
           }
           @case ('display') {
-            <section id="dock-panel-display" role="tabpanel" aria-labelledby="dock-tab-display" class="hud-acquire hud-brackets hud-surface pointer-events-auto mb-2 w-full max-w-lg px-4 py-3">
+            <section
+              id="dock-panel-display"
+              role="tabpanel"
+              aria-labelledby="dock-tab-display"
+              class="hud-acquire hud-brackets hud-surface pointer-events-auto mb-2 w-full max-w-lg px-4 py-3"
+            >
               <p class="type-label text-muted">Layers</p>
               <div class="mt-2 flex flex-wrap gap-2">
                 @for (layer of layers; track layer.key) {
@@ -185,18 +276,92 @@ function isWideViewport(): boolean {
                     [attr.aria-pressed]="isOn(layer.key)"
                     (click)="toggleLayer(layer.key)"
                     class="type-label flex items-center gap-2 border px-3 py-1.5 transition-colors focus-visible:outline-1 focus-visible:-outline-offset-1 focus-visible:outline-accent"
-                    [class]="isOn(layer.key) ? 'border-accent/60 bg-accent/12 text-accent hover:bg-accent/18' : 'border-border/60 text-muted hover:border-border hover:text-text'"
+                    [class]="
+                      isOn(layer.key)
+                        ? 'border-accent/60 bg-accent/12 text-accent hover:bg-accent/18'
+                        : 'border-border/60 text-muted hover:border-border hover:text-text'
+                    "
                   >
                     <!-- The state mark: a filled tick when the layer is drawn, hollow when it is not. -->
-                    <span aria-hidden="true" class="h-1.5 w-1.5 border border-current" [class.bg-current]="isOn(layer.key)"></span>
+                    <span
+                      aria-hidden="true"
+                      class="h-1.5 w-1.5 border border-current"
+                      [class.bg-current]="isOn(layer.key)"
+                    ></span>
                     {{ layer.label }}
                   </button>
                 }
               </div>
+
+              <!-- The clock. Orbits and rotations are both functions of a date, so this is the
+                   difference between a still picture and an orrery. -->
+              <p class="type-label mt-4 text-muted">Clock</p>
+              <!-- Radios rather than buttons: the rates are one-of-four, and the native control
+                   carries that to a screen reader and to the arrow keys without any script. -->
+              <div
+                class="mt-2 flex flex-wrap items-center gap-2"
+                role="radiogroup"
+                aria-label="Clock rate"
+              >
+                @for (rate of timeRates; track rate.secondsPerSecond) {
+                  <label
+                    class="type-label cursor-pointer border px-3 py-1.5 transition-colors has-[:focus-visible]:outline has-[:focus-visible]:outline-1 has-[:focus-visible]:-outline-offset-1 has-[:focus-visible]:outline-accent"
+                    [class]="
+                      time.rate() === rate.secondsPerSecond
+                        ? 'border-accent/60 bg-accent/12 text-accent hover:bg-accent/18'
+                        : 'border-border/60 text-muted hover:border-border hover:text-text'
+                    "
+                  >
+                    <input
+                      type="radio"
+                      name="clock-rate"
+                      class="sr-only"
+                      [value]="rate.secondsPerSecond"
+                      [checked]="time.rate() === rate.secondsPerSecond"
+                      (change)="time.setRate(rate.secondsPerSecond)"
+                    />
+                    {{ rate.label }}
+                  </label>
+                }
+                @if (!time.atNow()) {
+                  <button
+                    type="button"
+                    (click)="time.reset()"
+                    class="type-label border border-border/60 px-3 py-1.5 text-muted transition-colors hover:border-accent/70 hover:text-accent focus-visible:outline-1 focus-visible:-outline-offset-1 focus-visible:outline-accent"
+                  >
+                    Back to now
+                  </button>
+                }
+              </div>
             </section>
           }
         }
       }
+      <!-- Hidden rather than unmounted: the departure, destination and range it holds would
+           otherwise reset on every trip to another tab, while the scene kept drawing the graph at
+           the old range. No acquire wipe, unlike the panels around it: this is the one that comes
+           back with what it had, so it is not acquiring anything — and for the 380 ms the wipe
+           runs, its clip path swallows clicks on the suggestions it just brought back. -->
+      @if (routing()) {
+        <section
+          id="dock-panel-routes"
+          role="tabpanel"
+          aria-labelledby="dock-tab-routes"
+          [hidden]="activeTab() !== 'routes'"
+          class="hud-brackets hud-surface pointer-events-auto mb-2 w-full max-w-xl px-4 py-3"
+        >
+          <app-routes-panel
+            [result]="routeResult()"
+            [pending]="routePending()"
+            [options]="routeOptions()"
+            [currentStar]="currentStar()"
+            (queryChange)="routeQuery.emit($event)"
+            (routeRequested)="routeRequested.emit($event)"
+            (starSelected)="onRouteStarSelected($event)"
+            (rangeChange)="jumpRangeChange.emit($event)"
+          />
+        </section>
+      }
 
       <div class="hud-brackets hud-surface pointer-events-auto flex w-full items-stretch">
         <div role="tablist" aria-label="Dock" class="flex items-stretch divide-x divide-border/40">
@@ -209,21 +374,39 @@ function isWideViewport(): boolean {
               [attr.aria-controls]="activeTab() === tab ? 'dock-panel-' + tab : null"
               (click)="toggleTab(tab)"
               class="type-eyebrow px-3 py-2 transition-colors focus-visible:outline-1 focus-visible:-outline-offset-1 focus-visible:outline-accent sm:px-4"
-              [class]="activeTab() === tab ? 'bg-accent/15 text-accent' : 'text-muted hover:bg-accent/8 hover:text-accent'"
+              [class]="
+                activeTab() === tab
+                  ? 'bg-accent/15 text-accent'
+                  : 'text-muted hover:bg-accent/8 hover:text-accent'
+              "
             >
               {{ tabLabel(tab) }}
             </button>
           }
         </div>
+        <!-- Only while the map is away from the present: at the present the date is
+             today's, which the reader's own machine already says. -->
+        @if (date()) {
+          <p
+            class="ml-auto flex items-baseline gap-2 border-l border-border/40 px-3 py-2 sm:px-4"
+            data-testid="hud-date"
+          >
+            <span class="type-label text-muted">Date</span>
+            <span class="text-sm text-accent tabular-nums">{{ date() }}</span>
+          </p>
+        }
         @if (range()) {
-          <p class="ml-auto flex items-baseline gap-2 border-l border-border/40 px-3 py-2 sm:px-4">
+          <p
+            class="flex items-baseline gap-2 border-l border-border/40 px-3 py-2 sm:px-4"
+            [class.ml-auto]="!date()"
+          >
             <span class="type-label text-muted">Range</span>
             <span class="text-sm text-accent tabular-nums">{{ range() }}</span>
           </p>
         }
       </div>
     </div>
-  `
+  `,
 })
 export class HudDockComponent implements OnInit {
   /** Readout panel contents. An empty title means there is nothing to read out, and no tab for it. */
@@ -235,12 +418,15 @@ export class HudDockComponent implements OnInit {
   readonly note = input('');
   /** Camera range, pre-formatted by the scene, which is the only thing that knows the units. */
   readonly range = input('');
+  /** The date the sky is drawn for; empty while the map is drawn for the present. */
+  readonly date = input('');
   /** Layer state; `null` means the surface has no layers to toggle and no Display tab. */
   readonly display = input<HudDisplay | null>(null);
   /** Which panel is open on a wide viewport when the dock mounts. */
   readonly defaultTab = input<DockTab | null>(null);
   /** Routing: what the scene found, what it offers for the fields, and where the view is. */
   readonly routeResult = input<RouteResult | null>(null);
+  readonly routePending = input(false);
   readonly routeOptions = input<readonly RouteStarOption[]>([]);
   readonly currentStar = input<RouteStarOption | null>(null);
   /** The star the readout is about, where there is one to keep — a scale is not a place. */
@@ -264,12 +450,14 @@ export class HudDockComponent implements OnInit {
     // Always offered, even with nothing in it: it is the only place that says the map can keep
     // anything at all, and a tab that appears once you already know is a tab that never taught.
     'bookmarks',
-    ...(this.display() ? (['display'] as const) : [])
+    ...(this.display() ? (['display'] as const) : []),
   ]);
 
   readonly activeTab = signal<DockTab | null>(null);
 
   readonly bookmarks = inject(BookmarksStore);
+  readonly time = inject(TimeStore);
+  readonly timeRates = TIME_RATES;
 
   private readonly search = viewChild(SearchComponent);
   private readonly host = inject<ElementRef<HTMLElement>>(ElementRef);
@@ -324,7 +512,10 @@ export class HudDockComponent implements OnInit {
       return;
     }
     const target = event.target as HTMLElement | null;
-    if (target && (target.tagName === 'INPUT' || target.tagName === 'TEXTAREA' || target.isContentEditable)) {
+    if (
+      target &&
+      (target.tagName === 'INPUT' || target.tagName === 'TEXTAREA' || target.isContentEditable)
+    ) {
       return;
     }
     event.preventDefault();
@@ -336,7 +527,11 @@ export class HudDockComponent implements OnInit {
   /** On a narrow viewport the panel is a sheet over the scene: tapping the scene folds it away. */
   @HostListener('document:pointerdown', ['$event'])
   onDocumentPointerDown(event: PointerEvent): void {
-    if (this.activeTab() && !isWideViewport() && !this.host.nativeElement.contains(event.target as Node)) {
+    if (
+      this.activeTab() &&
+      !isWideViewport() &&
+      !this.host.nativeElement.contains(event.target as Node)
+    ) {
       this.activeTab.set(null);
     }
   }

src/app/features/hud/routes-panel.component.ts

@@ -2,6 +2,12 @@ import { ChangeDetectionStrategy, Component, computed, input, output, signal } f
 
 import { formatParsecs } from '../../shared/format/quantity';
 
+/**
+ * The widest jump the Routes panel offers. Past it the drawn graph is a solid sheet of lines, and
+ * a route search through the dense core around the Sun walks thousands of stars at every step.
+ */
+export const MAX_JUMP_RANGE_PC = 8;
+
 /** A star offered for one of the two fields, as the panel needs to show it. */
 export interface RouteStarOption {
   readonly id: number;
@@ -14,8 +20,12 @@ export interface RouteResult {
   /** The chain, departure first. Empty when there is no route at the range asked for. */
   readonly stars: readonly { id: number; name: string }[];
   readonly totalPc: number;
-  /** The shortest range that would open a route, where none was found at the one asked for. */
+  /** A range that would open a route, where none was found at the one asked for. */
   readonly neededRangePc: number | null;
+  /** True when the search gave up rather than showing there is no route at this range. */
+  readonly gaveUp: boolean;
+  /** True when the search for a range that would work looked everywhere up to the widest offered. */
+  readonly least: boolean;
 }
 
 export interface RouteRequest {
@@ -94,11 +104,11 @@ type Field = 'from' | 'to';
       <div class="flex items-center gap-3">
         <button
           type="button"
-          [disabled]="!canPlot()"
+          [disabled]="!canPlot() || pending()"
           (click)="plot()"
           class="type-label border border-border/60 px-3 py-1.5 text-muted transition-colors enabled:hover:border-accent/70 enabled:hover:text-accent disabled:opacity-40 focus-visible:outline-1 focus-visible:-outline-offset-1 focus-visible:outline-accent"
         >
-          Plot route
+          {{ pending() ? 'Plotting…' : 'Plot route' }}
         </button>
         @if (result(); as plotted) {
           @if (plotted.stars.length) {
@@ -107,17 +117,22 @@ type Field = 'from' | 'to';
             </p>
           } @else {
             <p data-testid="route-summary" class="text-sm text-muted">
+              @if (plotted.gaveUp) {
+                Too many stars to search at this range.
+              } @else {
                 No route at this range.
+              }
               @if (plotted.neededRangePc !== null) {
                 <button
                   type="button"
+                  [disabled]="!canPlot() || pending()"
                   (click)="raiseTo(plotted.neededRangePc)"
-                  class="text-accent underline decoration-accent/40 underline-offset-2 hover:decoration-accent focus-visible:outline-1 focus-visible:outline-accent"
+                  class="text-accent underline decoration-accent/40 underline-offset-2 disabled:opacity-40 disabled:no-underline enabled:hover:decoration-accent focus-visible:outline-1 focus-visible:outline-accent"
                 >
                   {{ format(plotted.neededRangePc) }} would reach.
                 </button>
-              } @else {
+              } @else if (plotted.least) {
-                Nothing in the catalogue bridges the gap.
+                No chain of jumps up to {{ format(maxRangePc) }} reaches it.
               }
             </p>
           }
@@ -148,6 +163,8 @@ export class RoutesPanelComponent {
   readonly result = input<RouteResult | null>(null);
   /** Matches for the field currently being typed into, ranked by the scene. */
   readonly options = input<readonly RouteStarOption[]>([]);
+  /** The scene is still working the last request out; asking again would only queue behind it. */
+  readonly pending = input(false);
   /** The star the view is currently inside, offered as the departure without typing. */
   readonly currentStar = input<RouteStarOption | null>(null);
 
@@ -160,8 +177,7 @@ export class RoutesPanelComponent {
   readonly fields: readonly Field[] = ['from', 'to'];
   /** A tenth of a parsec is finer than the catalogue's own distances are known to. */
   readonly minRangePc = 0.5;
-  /** Beyond this the graph is a solid sheet of lines and every pair of stars is connected. */
+  readonly maxRangePc = MAX_JUMP_RANGE_PC;
-  readonly maxRangePc = 8;
 
   readonly rangePc = signal(3);
   readonly open = signal<Field | null>(null);
@@ -169,8 +185,14 @@ export class RoutesPanelComponent {
   private readonly chosen = signal<Record<Field, RouteStarOption | null>>({ from: null, to: null });
   private readonly typed = signal<Record<Field, string>>({ from: '', to: '' });
 
-  /** Departure falls back to wherever the view already is, so one field is usually enough. */
+  /**
-  private readonly departure = computed(() => this.chosen().from ?? this.currentStar());
+   * Departure falls back to wherever the view already is, so one field is usually enough — but only
+   * while the field is empty. Text left in it that names no chosen star used to fall back all the
+   * same, so the panel read "Sol" and the route left from whatever the view had since flown to.
+   */
+  // Trimmed, as the scene trims the same text before offering matches for it: a field holding one
+  // space looks empty, offers nothing to choose, and would otherwise count as a departure.
+  private readonly departure = computed(() => this.chosen().from ?? (this.typed().from.trim() ? null : this.currentStar()));
 
   readonly canPlot = computed(() => this.departure() !== null && this.chosen().to !== null);
   readonly rangeLabel = computed(() => formatParsecs(this.rangePc()));

src/app/shared/astro/brightest.spec.ts

@@ -0,0 +1,90 @@
+import { describe, expect, it } from 'vitest';
+
+import { brightestWithin, brightnessIndex, brightnessOrder } from './brightest';
+
+interface TestStar {
+  id: number;
+  x: number;
+  y: number;
+  z: number;
+  magnitude: number;
+}
+
+/** A pseudo-random cloud with repeated magnitudes, so ties are exercised. */
+function cloud(count: number): TestStar[] {
+  let seed = 5;
+  const random = () => (seed = (seed * 1103515245 + 12345) % 2147483648) / 2147483648;
+  return Array.from({ length: count }, (_, id) => ({
+    id: id * 7,
+    x: random() * 200 - 100,
+    y: random() * 200 - 100,
+    z: random() * 200 - 100,
+    magnitude: Math.round(random() * 40) / 4
+  }));
+}
+
+describe('brightnessOrder', () => {
+  it('puts the brightest first and keeps catalogue order among equals', () => {
+    const stars = [{ magnitude: 5 }, { magnitude: -1 }, { magnitude: 5 }, { magnitude: 2 }];
+
+    expect(Array.from(brightnessOrder(stars))).toEqual([1, 3, 0, 2]);
+  });
+
+  it('orders nothing for an empty catalogue', () => {
+    expect(brightnessOrder([])).toHaveLength(0);
+  });
+});
+
+describe('brightestWithin', () => {
+  // What the labels used to do on every pass: filter the whole catalogue, then sort what was left.
+  function filterThenSort(stars: TestStar[], centre: { x: number; y: number; z: number }, radius: number, alwaysId: number | null): number[] {
+    return stars
+      .filter((star) => Math.hypot(star.x - centre.x, star.y - centre.y, star.z - centre.z) <= radius || star.id === alwaysId)
+      .sort((a, b) => a.magnitude - b.magnitude)
+      .map((star) => star.id);
+  }
+
+  it('yields exactly what filtering and then sorting the catalogue did, in the same order', () => {
+    const stars = cloud(3000);
+    const index = brightnessIndex(stars);
+    const centre = { x: 12, y: -30, z: 5 };
+
+    for (const [radius, alwaysId] of [[40, null], [15, 7 * 2999], [0, 7 * 11], [500, null]] as const) {
+      const lazy = Array.from(brightestWithin(stars, index, centre, radius, alwaysId), (star) => star.id);
+      expect(lazy).toEqual(filterThenSort(stars, centre, radius, alwaysId));
+    }
+  });
+
+  it('includes a star lying exactly on the radius, as the scan it replaced did', () => {
+    const stars = [
+      { id: 1, x: 3, y: 4, z: 0, magnitude: 1 },
+      { id: 2, x: 3, y: 4.001, z: 0, magnitude: 0 }
+    ];
+
+    expect(Array.from(brightestWithin(stars, brightnessIndex(stars), { x: 0, y: 0, z: 0 }, 5, null), (star) => star.id)).toEqual([1]);
+  });
+
+  it('reads no further than the caller takes', () => {
+    const stars = cloud(3000);
+    let read = 0;
+    const counted = new Proxy(stars, {
+      get(target, key, receiver) {
+        if (typeof key === 'string' && /^\d+$/.test(key)) {
+          read++;
+        }
+        return Reflect.get(target, key, receiver);
+      }
+    });
+
+    const taken: number[] = [];
+    for (const star of brightestWithin(counted, brightnessIndex(stars), { x: 0, y: 0, z: 0 }, 1000, null)) {
+      taken.push(star.id);
+      if (taken.length === 15) {
+        break;
+      }
+    }
+
+    expect(taken).toHaveLength(15);
+    expect(read).toBe(15);
+  });
+});

src/app/shared/astro/brightest.ts

@@ -0,0 +1,87 @@
+/**
+ * The catalogue in order of brightness, worked out once and walked as often as needed.
+ *
+ * Two parts of the map want "the brightest stars in this region": the labels, which name about
+ * fifteen of them five times a second, and the star field, which draws a budget of them. Sorting
+ * the region each time is paid for every star in it. At the opening view the label region holds
+ * some 60 000 stars, and sorting them to name fifteen took 55-70 ms a pass, a stall five times
+ * a second on any machine. Walking one shared order and stopping when enough have been taken
+ * costs only the stars looked at before that.
+ */
+
+export interface BrightnessRanked {
+  readonly magnitude: number;
+}
+
+export interface Positioned {
+  readonly x: number;
+  readonly y: number;
+  readonly z: number;
+}
+
+/**
+ * Indices into `stars`, brightest (lowest magnitude) first. Ties keep catalogue order: typed-array
+ * sort is required to be stable, exactly as the sort of the stars themselves was.
+ */
+export function brightnessOrder(stars: readonly BrightnessRanked[]): Uint32Array {
+  // Compared from a typed copy rather than off the stars: the sort reads two magnitudes per
+  // comparison, some eight million times for the whole catalogue: 83 ms this way, 104-139 ms reading them off the stars.
+  const magnitudes = Float64Array.from(stars, (star) => star.magnitude);
+  return Uint32Array.from(stars.keys()).sort((a, b) => magnitudes[a] - magnitudes[b]);
+}
+
+/**
+ * The brightness order, with each star's position and id laid out beside it in that order.
+ *
+ * A walk has to test every star it passes, and near the Sun it passes nearly all of them: a 4 pc
+ * label radius holds a few dozen stars, faint dwarfs deep in the order, so the walk rarely finds
+ * fifteen to name before the end. Reading the stars themselves in brightness order jumps all over
+ * the catalogue, and a full walk took 19-23 ms — slower than the scan and sort it replaced. Read
+ * from these arrays, laid out in the order they are walked, the same walk touches memory in
+ * sequence and reads a star only when it yields one.
+ */
+export interface BrightnessIndex {
+  /** Indices into the catalogue, brightest first. */
+  readonly order: Uint32Array;
+  /** Positions in the same order, three to a star, at full precision so a star on a radius stays on it. */
+  readonly positions: Float64Array;
+  readonly ids: Float64Array;
+}
+
+export function brightnessIndex<T extends BrightnessRanked & Positioned & { readonly id: number }>(stars: readonly T[]): BrightnessIndex {
+  const order = brightnessOrder(stars);
+  const positions = new Float64Array(order.length * 3);
+  const ids = new Float64Array(order.length);
+  order.forEach((index, at) => {
+    const star = stars[index];
+    positions[at * 3] = star.x;
+    positions[at * 3 + 1] = star.y;
+    positions[at * 3 + 2] = star.z;
+    ids[at] = star.id;
+  });
+  return { order, positions, ids };
+}
+
+/**
+ * The stars within `radiusPc` of `centre`, brightest first, plus the one star `alwaysId` names
+ * wherever it is — handed over lazily, so a caller that stops after the first few pays for no
+ * more than it read.
+ */
+export function* brightestWithin<T extends BrightnessRanked & Positioned & { readonly id: number }>(
+  stars: readonly T[],
+  index: BrightnessIndex,
+  centre: Positioned,
+  radiusPc: number,
+  alwaysId: number | null
+): Generator<T> {
+  const { order, positions, ids } = index;
+  const radiusSq = radiusPc * radiusPc;
+  for (let at = 0; at < order.length; at++) {
+    const dx = positions[at * 3] - centre.x;
+    const dy = positions[at * 3 + 1] - centre.y;
+    const dz = positions[at * 3 + 2] - centre.z;
+    if (dx * dx + dy * dy + dz * dz <= radiusSq || ids[at] === alwaysId) {
+      yield stars[order[at]];
+    }
+  }
+}

src/app/shared/astro/coordinates.spec.ts

@@ -7,6 +7,7 @@ import {
   OBLIQUITY_J2000_DEG,
   parallaxMasToParsecs,
   parseSexagesimal,
+  propagateProperMotion,
   raDecDistanceToXyz,
   raDecToUnitVector,
   raDegDecDistanceToXyz
@@ -59,6 +60,27 @@ describe('raDegDecDistanceToXyz', () => {
   });
 });
 
+describe('propagateProperMotion', () => {
+  it("carries Barnard's Star from Gaia's epoch back to HYG's", () => {
+    // Gaia DR3 4472832130942575872 as published for J2016.0, moved back sixteen years with its
+    // own proper motion, lands on the J2000.0 position SIMBAD lists to a milliarcsecond — and
+    // 0.08″ from where HYG has Barnard's Star, instead of the 166″ the two epochs put between them.
+    const j2000 = propagateProperMotion(269.44850252543836, 4.739420051112412, -801.550978, 10362.394207, -16);
+    expect(j2000.raDeg).toBeCloseTo(269.4520772, 6);
+    expect(j2000.decDeg).toBeCloseTo(4.693365, 6);
+  });
+
+  it('divides the right-ascension motion by cos δ, since pmra is published on the sky', () => {
+    // 3600 mas/yr for one year is 3.6″ on the sky; at Dec 60° that is 7.2″ of right ascension.
+    expect(propagateProperMotion(0, 60, 3600, 0, 1).raDeg).toBeCloseTo(7.2 / 3600, 9);
+    expect(propagateProperMotion(0, 60, 0, 3600, 1).decDeg).toBeCloseTo(60 + 3.6 / 3600, 9);
+  });
+
+  it('leaves a star with no proper motion where it is', () => {
+    expect(propagateProperMotion(100, -20, 0, 0, 16)).toEqual({ raDeg: 100, decDeg: -20 });
+  });
+});
+
 describe('parallaxMasToParsecs', () => {
   it('converts a positive parallax to the expected distance', () => {
     expect(parallaxMasToParsecs(769.33)).toBeCloseTo(1.3, 2); // Proxima Centauri

src/app/shared/astro/coordinates.ts

@@ -33,6 +33,21 @@ export function raDegDecDistanceToXyz(raDeg: number, decDeg: number, distancePc:
   return raDecDistanceToXyz(raDeg / HOURS_TO_DEG, decDeg, distancePc);
 }
 
+const MAS_TO_DEG = 1 / 3_600_000;
+
+/**
+ * Moves a sky position along its proper motion by `years` — negative to go back in time — so
+ * catalogues that observed at different epochs can be compared at one. `pmRaMasPerYear` is
+ * μα cos δ, the on-sky rate Hipparcos and Gaia both publish, hence the division by cos δ to turn
+ * it back into right ascension.
+ */
+export function propagateProperMotion(raDeg: number, decDeg: number, pmRaMasPerYear: number, pmDecMasPerYear: number, years: number): { raDeg: number; decDeg: number } {
+  return {
+    raDeg: raDeg + (years * pmRaMasPerYear * MAS_TO_DEG) / Math.cos(decDeg * DEG_TO_RAD),
+    decDeg: decDeg + years * pmDecMasPerYear * MAS_TO_DEG
+  };
+}
+
 /**
  * Obliquity of the ecliptic at J2000.0, in degrees — the tilt of Earth's orbital plane against
  * its equator, and so the angle between this app's two source frames.

src/app/shared/astro/host-star-matching.spec.ts

@@ -1,9 +1,14 @@
 import { describe, expect, it } from 'vitest';
 
 import { buildStarNameIndex, normalizeStarName, resolveHostStarId } from './host-star-matching';
+import { propagateProperMotion, raDegDecDistanceToXyz } from './coordinates';
 import { StarRecord } from '../models/star.model';
 
-// A small fixture standing in for a slice of the HYG star index, used to exercise the
+function star(id: number, name: string, raDeg: number, decDeg: number, distancePc: number): StarRecord {
+  return { id, name, ...raDegDecDistanceToXyz(raDeg, decDeg, distancePc), magnitude: 10, spectralType: 'M', colorIndex: 1.0 };
+}
+
+// A small fixture standing in for a slice of the star catalogue, used to exercise the
 // exoplanet host-star cross-referencing logic without hitting any real API.
 const FIXTURE_STARS: StarRecord[] = [
   // The Sun sits at the origin, exactly where a host with a missing distance lands.
@@ -22,46 +27,150 @@ describe('normalizeStarName', () => {
 
 describe('resolveHostStarId', () => {
   it('matches by exact (normalized) host star name', () => {
-    const id = resolveHostStarId({ hostname: 'Proxima Centauri', raDeg: NaN, decDeg: NaN, distancePc: NaN }, FIXTURE_STARS, 0.5);
+    const id = resolveHostStarId({ hostname: 'Proxima Centauri', raDeg: NaN, decDeg: NaN, distancePc: NaN }, FIXTURE_STARS);
 
     expect(id).toBe(1);
   });
 
   it('matches by name regardless of case/spacing differences', () => {
-    const id = resolveHostStarId({ hostname: 'gj3512', raDeg: NaN, decDeg: NaN, distancePc: NaN }, FIXTURE_STARS, 0.5);
+    const id = resolveHostStarId({ hostname: 'gj3512', raDeg: NaN, decDeg: NaN, distancePc: NaN }, FIXTURE_STARS);
 
     expect(id).toBe(3);
   });
 
-  it('falls back to nearest-neighbour position matching when the name is unknown', () => {
+  it('returns null when there is no name match and no position is available', () => {
-    // Slightly off from Sirius's exact position, within tolerance.
+    const id = resolveHostStarId({ hostname: 'Unknown Star XYZ', raDeg: NaN, decDeg: NaN, distancePc: NaN }, FIXTURE_STARS);
-    const id = resolveHostStarId({ hostname: 'Sirius A', raDeg: 101.29, decDeg: -16.72, distancePc: 2.64 }, FIXTURE_STARS, 0.5);
+
+    expect(id).toBeNull();
+  });
+
+  describe('matching on the sky', () => {
+    // GJ 887's archive row: position at Gaia's epoch, carried by 6.9″/yr of proper motion —
+    // 110″ from where the catalogue has the star at J2000. The matcher must carry the query
+    // back those sixteen years itself, and judge each star on the better of the two epochs: the
+    // decoy standing halfway along the star's own track is nearer than Lacaille 9352 at the
+    // published point *and* nearer at the worse of the two epochs, so it wins unless the
+    // carried-back position is tried and the best epoch — not the worst — decides.
+    it('matches a host published at the Gaia epoch to its star at J2000, past a decoy on its track', () => {
+      const lacaille9352 = star(70, 'Lacaille 9352', 346.46683, -35.85306, 3.29);
+      const archive = propagateProperMotion(346.46683, -35.85306, 6768.2, 1327.52, 16);
+      const decoy = star(71, 'Decoy', (346.46683 + archive.raDeg) / 2, (-35.85306 + archive.decDeg) / 2, 3.29);
+
+      const id = resolveHostStarId(
+        { hostname: 'GJ 887', raDeg: archive.raDeg, decDeg: archive.decDeg, distancePc: 3.28679, pmRaMasPerYear: 6768.2, pmDecMasPerYear: 1327.52 },
+        [decoy, lacaille9352]
+      );
+
+      expect(id).toBe(70);
+    });
+
+    // alf Tau's archive row publishes J2000 outright, and the archive never says which epoch a
+    // row is at. If the matcher trusted one epoch and carried every query back, Aldebaran's
+    // planet would land on the Gliese entry sitting 3″ from the carried-back point; the raw
+    // position, zero arcseconds from Aldebaran itself, has to win.
+    it('keeps a host published at J2000 on its star, proper motion or not', () => {
+      const aldebaran = star(80, 'Aldebaran', 68.980163, 16.509302, 20.43);
+      const carried = propagateProperMotion(68.980163, 16.509302, 63, -189, -16);
+      const ghost = star(81, 'Gl 171.1B', carried.raDeg, carried.decDeg + 3 / 3600, 20.43);
+
+      const id = resolveHostStarId(
+        { hostname: 'alf Tau', raDeg: 68.980163, decDeg: 16.509302, distancePc: 20.43, pmRaMasPerYear: 63, pmDecMasPerYear: -189 },
+        [ghost, aldebaran]
+      );
+
+      expect(id).toBe(80);
+    });
+
+    // GJ 15 A's archive row sits at J2016, 46″ along its proper motion from Groombridge 34's
+    // J2000 place — and only 16″ from an unrelated Gaia entry. Nearest-to-the-published-point
+    // picks the interloper; carrying the query back the sixteen years must put the planets on
+    // the star that actually moved there.
+    it('picks the star the proper motion says the query is, not the entry nearest the published point', () => {
+      const primary = star(90, 'Groombridge 34', 4.595364, 44.022955, 3.562);
+      const published = propagateProperMotion(4.595364, 44.022955, 2891.5, 411.9, 16);
+      const interloper = star(91, 'Gaia DR3 385334196532776576', published.raDeg, published.decDeg + 16 / 3600, 3.563);
+
+      const id = resolveHostStarId(
+        { hostname: 'GJ 15 A', raDeg: published.raDeg, decDeg: published.decDeg, distancePc: 3.56228, pmRaMasPerYear: 2891.5, pmDecMasPerYear: 411.9 },
+        [interloper, primary]
+      );
+
+      expect(id).toBe(90);
+    });
+
+    // GJ 273 is Luyten's Star to the arcsecond, but the archive publishes 5.92 pc for a star
+    // at 3.79 — a 56% disagreement. Direction alone must not override a distance in flat
+    // contradiction, or every line-of-sight coincidence becomes a match.
+    it('refuses a host whose distance flatly contradicts the star it points at', () => {
+      const luytens = star(100, "Luyten's Star", 111.8496, 5.2258, 3.79);
+
+      const id = resolveHostStarId({ hostname: 'GJ 273', raDeg: 111.8496, decDeg: 5.2258, distancePc: 5.921535 }, [luytens]);
+
+      expect(id).toBeNull();
+    });
+
+    // The tolerance is transverse — parsecs on the sky, not an angle — so the same 15″ offset
+    // is a match at 50 pc and a stranger at 200 pc.
+    it('scales the angular tolerance with the host distance', () => {
+      const at200 = resolveHostStarId(
+        { hostname: 'Unmatched', raDeg: 150, decDeg: -40 + 15 / 3600, distancePc: 200 },
+        [star(110, 'Far', 150, -40, 200)]
+      );
+      const at50 = resolveHostStarId(
+        { hostname: 'Unmatched', raDeg: 150, decDeg: -40 + 15 / 3600, distancePc: 50 },
+        [star(111, 'Near', 150, -40, 50)]
+      );
+
+      expect(at200).toBeNull();
+      expect(at50).toBe(111);
+    });
+
+    // A star whose distance disqualifies it is not merely rejected — it must not become the
+    // best-so-far either, or an unmerged twin with a bad parallax, sitting nearer on the sky
+    // than the true host, silently unhosts the planet by outranking a star that is never
+    // allowed to win.
+    it('does not let a star its distance disqualifies shadow the true host behind it', () => {
+      const badParallaxTwin = star(120, 'Gaia DR3 twin', 40, 12 + 1 / 3600, 480);
+      const host = star(121, 'True host', 40, 12 + 3 / 3600, 100);
+
+      const id = resolveHostStarId({ hostname: 'Unmatched', raDeg: 40, decDeg: 12, distancePc: 100 }, [badParallaxTwin, host]);
+
+      expect(id).toBe(121);
+    });
+
+    // A proper motion that is not a number must not poison the comparison: NaN loses every
+    // `<` it appears in, so an unguarded one lets each star past the direction test and hands
+    // the planet to whichever happens to be last in the catalogue.
+    it('treats an unusable proper motion as no motion rather than matching by array order', () => {
+      const pointedAt = star(130, 'Pointed at', 10, 10, 5);
+      const acrossTheSky = star(131, 'Across the sky', 190, -10, 5);
+
+      const id = resolveHostStarId(
+        { hostname: 'Unmatched', raDeg: 10, decDeg: 10, distancePc: 5, pmRaMasPerYear: NaN, pmDecMasPerYear: 0 },
+        [pointedAt, acrossTheSky]
+      );
+
+      expect(id).toBe(130);
+    });
+
+    // Normalizing strips the dot, so `Gl 55.2` and `Gl 552` — two stars 135° apart — answer to
+    // one key. A name that names both names neither: the sky has to settle it.
+    it('sends a name two stars answer to back to the sky', () => {
+      const gl552 = star(140, 'Gl 552', 217.0, 15.0, 14.2);
+      const gl55dot2 = star(141, 'Gl 55.2', 30.0, -20.0, 23.9);
+
+      const id = resolveHostStarId({ hostname: 'Gl 552', raDeg: 217.0, decDeg: 15.0, distancePc: 14.2 }, [gl552, gl55dot2]);
+
+      expect(id).toBe(140);
+    });
+
+    it('reuses a prebuilt name index when given one', () => {
+      const nameIndex = buildStarNameIndex(FIXTURE_STARS);
+
+      const id = resolveHostStarId({ hostname: 'Sirius', raDeg: NaN, decDeg: NaN, distancePc: NaN }, [], nameIndex);
 
       expect(id).toBe(2);
     });
-
-  it('returns null when no name match and no star is within tolerance', () => {
-    const id = resolveHostStarId({ hostname: 'Unknown Star XYZ', raDeg: 0, decDeg: 0, distancePc: 100 }, FIXTURE_STARS, 0.5);
-
-    expect(id).toBeNull();
-  });
-
-  it('returns null when there is no name match and no position is available', () => {
-    const id = resolveHostStarId({ hostname: 'Unknown Star XYZ', raDeg: NaN, decDeg: NaN, distancePc: NaN }, FIXTURE_STARS, 0.5);
-
-    expect(id).toBeNull();
-  });
-
-  it('picks the closest star when more than one falls within tolerance', () => {
-    const stars: StarRecord[] = [
-      { id: 10, name: 'Near', x: 0, y: 0, z: 0, magnitude: 5, spectralType: 'G', colorIndex: 0.5 },
-      { id: 11, name: 'Far', x: 0.4, y: 0, z: 0, magnitude: 5, spectralType: 'G', colorIndex: 0.5 }
-    ];
-    const nameIndex = buildStarNameIndex(stars);
-
-    const id = resolveHostStarId({ hostname: 'Unmatched', raDeg: 0, decDeg: 0, distancePc: 0.2 }, stars, 0.5, nameIndex);
-
-    expect(id).toBe(10);
   });
 
   describe('missing distance column', () => {
@@ -70,25 +179,25 @@ describe('resolveHostStarId', () => {
     // the Sun at distance 0. That shipped 127 alien planets, all seven TRAPPIST-1 worlds among
     // them, into our own solar system.
     it('does not match a host with a zero distance to the Sun', () => {
-      const id = resolveHostStarId({ hostname: 'TRAPPIST-1', raDeg: 346.6, decDeg: -5.04, distancePc: 0 }, FIXTURE_STARS, 0.5);
+      const id = resolveHostStarId({ hostname: 'TRAPPIST-1', raDeg: 346.6, decDeg: -5.04, distancePc: 0 }, FIXTURE_STARS);
 
       expect(id).toBeNull();
     });
 
     it('rejects a negative distance too', () => {
-      const id = resolveHostStarId({ hostname: 'Nowhere', raDeg: 10, decDeg: 10, distancePc: -3 }, FIXTURE_STARS, 0.5);
+      const id = resolveHostStarId({ hostname: 'Nowhere', raDeg: 10, decDeg: 10, distancePc: -3 }, FIXTURE_STARS);
 
       expect(id).toBeNull();
     });
 
     it('still matches a real host at a genuinely small distance', () => {
-      const id = resolveHostStarId({ hostname: 'Unmatched', raDeg: 217.4, decDeg: -62.68, distancePc: 1.2959 }, FIXTURE_STARS, 0.5);
+      const id = resolveHostStarId({ hostname: 'Unmatched', raDeg: 217.4, decDeg: -62.68, distancePc: 1.2959 }, FIXTURE_STARS);
 
       expect(id).toBe(1);
     });
 
     it('lets a named host resolve even with no usable distance', () => {
-      const id = resolveHostStarId({ hostname: 'Sirius', raDeg: 101.3, decDeg: -16.7, distancePc: 0 }, FIXTURE_STARS, 0.5);
+      const id = resolveHostStarId({ hostname: 'Sirius', raDeg: 101.3, decDeg: -16.7, distancePc: 0 }, FIXTURE_STARS);
 
       expect(id).toBe(2);
     });

src/app/shared/astro/host-star-matching.ts

@@ -1,5 +1,5 @@
-import { CartesianCoordinates, distanceBetween, raDegDecDistanceToXyz } from './coordinates';
+import { propagateProperMotion, raDegDecDistanceToXyz } from './coordinates';
-import { ExoplanetRecord } from '../models/exoplanet.model';
+import { MERGE_DISTANCE_RATIO_TOLERANCE } from './star-merge';
 import { StarRecord } from '../models/star.model';
 
 /** Normalizes a star name for comparison: lowercase, alphanumeric characters only. */
@@ -12,25 +12,92 @@ export interface HostStarQuery {
   raDeg: number;
   decDeg: number;
   distancePc: number;
-}
+  /** μα·cos δ in mas/yr, as the archive publishes it (`sy_pmra`); missing means unknown. */
-
+  pmRaMasPerYear?: number;
-/** Builds a lookup of normalized star name -> star, for fast repeated name matching. */
+  pmDecMasPerYear?: number;
-export function buildStarNameIndex(stars: readonly StarRecord[]): Map<string, StarRecord> {
-  return new Map(stars.map((star) => [normalizeStarName(star.name), star]));
 }
 
 /**
- * Cross-references an exoplanet host star to the HYG star index: first by (normalized)
+ * Builds a lookup of normalized star name -> star, for fast repeated name matching.
- * name, then by nearest-neighbour position matching within `toleranceInPc`. Returns `null`
+ *
+ * A name two stars answer to names neither: normalizing strips the dot, so `Gl 55.2` and
+ * `Gl 552` — 135° apart, and 64 such groups exist in the catalogue — collide on `gl552`, and a
+ * map would silently keep whichever came last. Ambiguous keys are dropped instead, which sends
+ * the query to the sky, where direction settles it.
+ */
+export function buildStarNameIndex(stars: readonly StarRecord[]): Map<string, StarRecord> {
+  const index = new Map<string, StarRecord>();
+  const ambiguous = new Set<string>();
+  for (const star of stars) {
+    const key = normalizeStarName(star.name);
+    if (index.has(key)) {
+      ambiguous.add(key);
+    } else {
+      index.set(key, star);
+    }
+  }
+  for (const key of ambiguous) {
+    index.delete(key);
+  }
+  return index;
+}
+
+/**
+ * How far, on the sky, a host may sit from a catalogue star and still be the same object —
+ * expressed as a transverse offset in parsecs (separation angle × the host's distance), not as
+ * an angle.
+ *
+ * The offset between the archive's position and ours is dominated by proper motion over an
+ * epoch difference, and that is a *physical* displacement: velocity × time, the same in parsecs
+ * at any distance. As an angle it is anything — Proxima's two positions are 60″ apart, a host at
+ * 100 pc moves under 2″ — so a fixed angle either loses the near, fast stars or drowns the far
+ * ones in neighbours. In parsecs the bound is one number: 25 years of an extreme 200 km/s
+ * transverse velocity is 5·10⁻³ pc.
+ *
+ * Measured on the 504 hosts whose archive name matches a catalogue name outright — true pairs,
+ * matched without coordinates: their transverse offset reaches 3.4·10⁻³ pc (5.0·10⁻³ before the
+ * epoch straddle below) and 0.01 pc doubles that. Chance stays out of reach: shifting every
+ * host a quarter of a degree finds nothing within the budget except Proxima's own entry, whose
+ * budget at 1.3 pc is wider than the shift itself.
+ */
+export const HOST_TRANSVERSE_TOLERANCE_PC = 0.01;
+
+/**
+ * The archive does not say which epoch a row's position is for, and they are demonstrably
+ * mixed: alf Tau and GJ 273 publish J2000 (the raw position sits under an arcsecond from our
+ * star, and carrying it back doubles the error), HD 133131 and TOI-2459 publish Gaia's J2016
+ * (the carried-back position lands to 0.1″). So every query is tried at both ends — as
+ * published, and carried back sixteen years with the archive's own proper motion — and a star
+ * is judged on whichever is closer. Guessing one epoch picks companions: assume J2016 and
+ * Aldebaran's planet lands on Gl 171.1B, assume J2000 and GJ 15 A's land on a Gaia entry
+ * 15.9″ out.
+ */
+const CATALOGUE_EPOCH = 2000.0;
+const ARCHIVE_LATEST_EPOCH = 2016.0;
+
+function knownMotion(masPerYear: number | undefined): number {
+  return Number.isFinite(masPerYear) ? (masPerYear as number) : 0;
+}
+
+/**
+ * Cross-references an exoplanet host star to the star catalogue: first by (normalized) name,
+ * then on the sky — the nearest star within {@link HOST_TRANSVERSE_TOLERANCE_PC} whose distance
+ * does not flatly contradict the archive's ({@link MERGE_DISTANCE_RATIO_TOLERANCE}, shared with
+ * the catalogue merge, which faces the same Hipparcos-vs-Gaia disagreements). Returns `null`
  * when neither approach finds a confident match, rather than guessing.
  *
+ * Identity lives in the direction, exactly as in `star-merge.ts`: the previous rule — nearest
+ * neighbour within half a parsec in 3D — turned into a ten-arcminute cone at 170 pc, handing
+ * planets of stars our catalogue does not contain to whatever bright star floated nearest
+ * (HATS-6 to HD 39500), while a 1 pc distance disagreement at 60 pc unhosted four bright
+ * giants' planets whose directions matched to two arcseconds.
+ *
  * `nameIndex` should be built once (via {@link buildStarNameIndex}) and reused across calls
  * when resolving many queries against the same star list.
  */
 export function resolveHostStarId(
   query: HostStarQuery,
   stars: readonly StarRecord[],
-  toleranceInPc: number,
   nameIndex: Map<string, StarRecord> = buildStarNameIndex(stars)
 ): number | null {
   const byName = nameIndex.get(normalizeStarName(query.hostname));
@@ -43,91 +110,49 @@ export function resolveHostStarId(
   }
 
   // A non-positive distance is never a real measurement, and it is the specific shape a
-  // missing CSV cell takes: `Number('')` is `0`, which passes the finiteness check above and
+  // missing CSV cell takes: `Number('')` is `0`. Without a believable distance there is no
-  // then places the host exactly at the origin — where it matches the Sun at distance 0 and
+  // transverse budget and no ratio test, so the position cannot speak.
-  // hands an alien planet to our own solar system.
   if (query.distancePc <= 0) {
     return null;
   }
 
-  const hostPosition = raDegDecDistanceToXyz(query.raDeg, query.decDeg, query.distancePc);
+  const published = raDegDecDistanceToXyz(query.raDeg, query.decDeg, 1);
-  return findNearestStarWithin(hostPosition, stars, toleranceInPc);
+  const carriedBack = propagateProperMotion(
-}
+    query.raDeg,
-
+    query.decDeg,
-function findNearestStarWithin(position: CartesianCoordinates, stars: readonly StarRecord[], toleranceInPc: number): number | null {
+    // A proper motion that is not a number must read as "stands still", not poison the
-  let closest: { id: number; distance: number } | null = null;
+    // comparison: one NaN makes every star's cosine NaN, and `NaN < min` is false, so every
-
+    // star would pass the direction test and the last one in array order would win.
-  for (const star of stars) {
+    knownMotion(query.pmRaMasPerYear),
-    const distance = distanceBetween(position, star);
+    knownMotion(query.pmDecMasPerYear),
-    if (distance <= toleranceInPc && (!closest || distance < closest.distance)) {
+    CATALOGUE_EPOCH - ARCHIVE_LATEST_EPOCH
-      closest = { id: star.id, distance };
-    }
-  }
-
-  return closest ? closest.id : null;
-}
-
-/**
- * Re-resolves every exoplanet's host star against a star catalogue.
- *
- * The cross-reference is a *derived* fact: it depends as much on which stars were loaded as on
- * the archive itself. When the catalogue reached 50 pc, 388 of the archive's 4735 named hosts
- * found a match and the other 4347 were carried and never drawn — not because their planets are
- * unknown, but because their star was out of range. Widening the catalogue rescues some of them,
- * and until the host coordinates were stored alongside each planet that meant re-downloading an
- * archive which is not always reachable.
- *
- * Records written before those coordinates were kept can still be matched *by name*, which needs
- * no coordinates at all — and that alone is worth doing, because a wider catalogue contains more
- * names. What such a record cannot do is disprove its existing match: a name miss means only
- * that the name missed, not that the star is absent. So those are upgraded where a match is
- * found and left alone otherwise, while records that do carry coordinates take the new result
- * outright, match or no match.
- */
-
-/** A host must sit within this many parsecs of a catalogue star to count as the same object. */
-export const HOST_MATCH_TOLERANCE_PC = 2;
-
-export interface RematchSummary {
-  total: number;
-  /** Records carrying host coordinates, and therefore eligible to be re-matched in full. */
-  resolvable: number;
-  matched: number;
-  gained: number;
-  lost: number;
-}
-
-export function rematchHostStars(exoplanets: ExoplanetRecord[], stars: readonly StarRecord[]): RematchSummary {
-  const nameIndex = buildStarNameIndex(stars);
-  const summary: RematchSummary = { total: exoplanets.length, resolvable: 0, matched: 0, gained: 0, lost: 0 };
-
-  for (const exoplanet of exoplanets) {
-    const { hostRaDeg, hostDecDeg, hostDistancePc } = exoplanet;
-    const positioned = hostRaDeg !== undefined && hostDecDeg !== undefined && hostDistancePc !== undefined;
-    if (positioned) {
-      summary.resolvable++;
-    }
-
-    const previous = exoplanet.hostStarId;
-    // With no coordinates the query still carries the host's name, and `resolveHostStarId` tries
-    // that first; the positional fallback simply declines to run on non-finite coordinates.
-    const resolved = resolveHostStarId(
-      { hostname: exoplanet.hostStarName, raDeg: hostRaDeg ?? Number.NaN, decDeg: hostDecDeg ?? Number.NaN, distancePc: hostDistancePc ?? Number.NaN },
-      stars,
-      HOST_MATCH_TOLERANCE_PC,
-      nameIndex
   );
+  const carried = raDegDecDistanceToXyz(carriedBack.raDeg, carriedBack.decDeg, 1);
 
-    exoplanet.hostStarId = positioned ? resolved : (resolved ?? previous);
+  const minCosine = Math.cos(Math.min(Math.PI, HOST_TRANSVERSE_TOLERANCE_PC / query.distancePc));
-    if (exoplanet.hostStarId !== null) {
+  let best: StarRecord | null = null;
-      summary.matched++;
+  let bestCosine = -2;
+  for (const star of stars) {
+    const starDistance = Math.hypot(star.x, star.y, star.z);
+    // The Sun sits at the origin and has no direction to compare; every real host is elsewhere.
+    if (starDistance === 0) {
+      continue;
     }
-    if (previous === null && exoplanet.hostStarId !== null) {
+    const cosine =
-      summary.gained++;
+      Math.max(
-    } else if (previous !== null && exoplanet.hostStarId === null) {
+        star.x * published.x + star.y * published.y + star.z * published.z,
-      summary.lost++;
+        star.x * carried.x + star.y * carried.y + star.z * carried.z
+      ) / starDistance;
+    if (cosine < minCosine || cosine <= bestCosine) {
+      continue;
     }
+    const [near, far] = query.distancePc < starDistance ? [query.distancePc, starDistance] : [starDistance, query.distancePc];
+    if ((far - near) / near > MERGE_DISTANCE_RATIO_TOLERANCE) {
+      continue;
+    }
+    best = star;
+    bestCosine = cosine;
   }
 
-  return summary;
+  return best ? best.id : null;
 }

src/app/shared/astro/host-star-rematch.spec.ts

@@ -1,82 +0,0 @@
-import { describe, expect, it } from 'vitest';
-
-import { ExoplanetRecord } from '../models/exoplanet.model';
-import { StarRecord } from '../models/star.model';
-import { rematchHostStars } from './host-star-matching';
-
-/** Two catalogue stars, one of which is only present in the wider of the two catalogues. */
-const NEARBY: StarRecord = { id: 100, name: 'Gl 357', x: 9, y: 0, z: 0, magnitude: 10.9, spectralType: 'K', colorIndex: 1.4 };
-const DISTANT: StarRecord = { id: 200, name: 'HD 33844', x: 0, y: 120, z: 0, magnitude: 7.7, spectralType: 'K0', colorIndex: 1.0 };
-
-const NARROW_CATALOGUE = [NEARBY];
-const WIDE_CATALOGUE = [NEARBY, DISTANT];
-
-function planet(overrides: Partial<ExoplanetRecord> = {}): ExoplanetRecord {
-  return { id: 'p', hostStarId: null, hostStarName: 'HD 33844', name: 'HD 33844 b', orbit: { semiMajorAxisAu: 1 }, ...overrides };
-}
-
-describe('rematchHostStars', () => {
-  it('rescues a host that the wider catalogue now contains, by name alone', () => {
-    // The whole point: the cross-reference is a fact about the catalogue as much as about the
-    // archive, so widening one ought to resolve hosts the other already knew about.
-    const planets = [planet()];
-    const summary = rematchHostStars(planets, WIDE_CATALOGUE);
-
-    expect(planets[0].hostStarId).toBe(DISTANT.id);
-    expect(summary.gained).toBe(1);
-    expect(summary.matched).toBe(1);
-  });
-
-  it('needs no coordinates to do it', () => {
-    // Which matters, because the shipped records were written before coordinates were kept.
-    const planets = [planet()];
-    expect(planets[0].hostRaDeg).toBeUndefined();
-    rematchHostStars(planets, WIDE_CATALOGUE);
-    expect(planets[0].hostStarId).toBe(DISTANT.id);
-  });
-
-  it('will not clear an existing match on a name miss when it has no coordinates', () => {
-    // A name miss says the name missed, not that the star is absent — and the earlier match may
-    // have been positional, from data this record no longer carries.
-    const planets = [planet({ hostStarId: 999, hostStarName: 'Some Survey Designation' })];
-    const summary = rematchHostStars(planets, WIDE_CATALOGUE);
-
-    expect(planets[0].hostStarId).toBe(999);
-    expect(summary.lost).toBe(0);
-    expect(summary.matched).toBe(1);
-  });
-
-  it('takes the new answer outright when the record does carry coordinates', () => {
-    // With coordinates the match can be redone in full, so its result is authoritative — a host
-    // that no longer resolves is cleared rather than left pointing at a star that may be gone.
-    const planets = [planet({ hostStarId: 999, hostStarName: 'Nowhere', hostRaDeg: 10, hostDecDeg: 10, hostDistancePc: 500 })];
-    const summary = rematchHostStars(planets, WIDE_CATALOGUE);
-
-    expect(planets[0].hostStarId).toBeNull();
-    expect(summary.resolvable).toBe(1);
-    expect(summary.lost).toBe(1);
-  });
-
-  it('matches a positioned host to the catalogue star at its coordinates', () => {
-    const planets = [planet({ hostStarName: 'unlisted alias', hostRaDeg: 90, hostDecDeg: 0, hostDistancePc: 120 })];
-    rematchHostStars(planets, WIDE_CATALOGUE);
-    expect(planets[0].hostStarId).toBe(DISTANT.id);
-  });
-
-  it('leaves a host that neither catalogue contains unmatched', () => {
-    const planets = [planet()];
-    const summary = rematchHostStars(planets, NARROW_CATALOGUE);
-
-    expect(planets[0].hostStarId).toBeNull();
-    expect(summary.matched).toBe(0);
-    expect(summary.gained).toBe(0);
-  });
-
-  it('counts every record it was given', () => {
-    const planets = [planet(), planet({ id: 'q', hostStarName: 'Gl 357' }), planet({ id: 'r', hostStarName: 'nobody' })];
-    const summary = rematchHostStars(planets, WIDE_CATALOGUE);
-
-    expect(summary.total).toBe(3);
-    expect(summary.matched).toBe(2);
-  });
-});

src/app/shared/astro/jump-links.spec.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 
-import { collectJumpLinks, minimumRangeBetween, routeBetween } from './jump-links';
+import { jumpLinkSegments, minimumRangeBetween, routeBetween } from './jump-links';
 import { StarNeighbourhood, StarPoint } from './star-neighbourhood';
 
 /** Stars a parsec apart along x, so a chain's length is the number of hops it takes. */
@@ -14,7 +14,7 @@ function index(points: StarPoint[]): StarNeighbourhood {
 
 describe('routeBetween', () => {
   it('walks the chain a hop at a time when that is all the range allows', () => {
-    const route = routeBetween(chain(5), 0, 4, 1.5);
+    const { route } = routeBetween(chain(5), 0, 4, 1.5);
 
     expect(route?.stars).toEqual([0, 1, 2, 3, 4]);
     expect(route?.totalPc).toBeCloseTo(4);
@@ -24,7 +24,7 @@ describe('routeBetween', () => {
   it('goes straight there when the range reaches, however many stars lie between', () => {
     // The direct crossing is never longer than a chain through anything — Euclid says so — so a
     // range that covers it makes it the answer, and the stars in between are just scenery.
-    const route = routeBetween(chain(5), 0, 4, 5);
+    const { route } = routeBetween(chain(5), 0, 4, 5);
 
     expect(route?.stars).toEqual([0, 4]);
     expect(route?.totalPc).toBeCloseTo(4);
@@ -33,7 +33,7 @@ describe('routeBetween', () => {
   it('picks the shorter of two ways round when neither is a straight line', () => {
     // 0 to 3 is 10 pc, out of a 6 pc range. Two ways round, both inside it: through 1, barely
     // off the line, or through 2, well off it. Shorter is what "the way there" means.
-    const route = routeBetween(
+    const { route } = routeBetween(
       index([
         { id: 0, x: 0, y: 0, z: 0 },
         { id: 1, x: 5, y: 0.5, z: 0 },
@@ -56,19 +56,19 @@ describe('routeBetween', () => {
       { id: 2, x: 20, y: 0, z: 0 }
     ]);
 
-    expect(routeBetween(split, 0, 2, 5)).toBeNull();
+    expect(routeBetween(split, 0, 2, 5)).toEqual({ route: null, gaveUp: false });
   });
 
   it('answers nothing for a star that is not there, or for going nowhere', () => {
     const line = chain(3);
 
-    expect(routeBetween(line, 0, 0, 2)).toBeNull();
+    expect(routeBetween(line, 0, 0, 2).route).toBeNull();
-    expect(routeBetween(line, 0, 99, 2)).toBeNull();
+    expect(routeBetween(line, 0, 99, 2).route).toBeNull();
-    expect(routeBetween(line, 0, 2, 0)).toBeNull();
+    expect(routeBetween(line, 0, 2, 0).route).toBeNull();
   });
 
   it('reports the longest hop, which is what the range has to cover', () => {
-    const route = routeBetween(
+    const { route } = routeBetween(
       index([
         { id: 0, x: 0, y: 0, z: 0 },
         { id: 1, x: 1, y: 0, z: 0 },
@@ -81,9 +81,110 @@ describe('routeBetween', () => {
 
     expect(route?.longestHopPc).toBeCloseTo(4);
   });
+
+  it('says it gave up rather than that there is no chain, once it has spent its budget', { timeout: 30_000 }, () => {
+    // Nothing reaches the island, but the crowd around the departure is larger than the budget, so
+    // the search stops without having looked everywhere the range reaches. Read as "no chain", that
+    // is a confident wrong answer — and the range search downstream would build on it.
+    // Cells sized for the range asked of them, as the real catalogue's are: a search that settles
+    // 40 000 stars scans every cell it touches 40 000 times.
+    const search = routeBetween(knotAndChain(1.5), 0, ISLAND, 1.5);
+
+    expect(search.route).toBeNull();
+    expect(search.gaveUp).toBe(true);
+  });
+
+  it('reports a dead end proved with the last star of the budget as a dead end, not a give-up', () => {
+    // Exactly the budget's worth of stars reach each other, and the destination is not among them.
+    // The search does look everywhere the range reaches, so "no chain" is what it found — but the
+    // set is full at the end of it, and a budget read off the settled count says it gave up.
+    const search = routeBetween(budgetExactly(), 0, BUDGET_ISLAND, 1.5);
+
+    expect(search).toEqual({ route: null, gaveUp: false });
+  });
+
+  it('heads for the destination rather than exhausting a dense knot around the departure', () => {
+    // The Gaia catalogue in miniature: a crowd around the departure, larger than the search's
+    // budget, with the only way on a thin chain leading out of it. A search widening evenly from
+    // the departure spends the budget on the crowd and never reaches the chain's far end.
+    const { route } = routeBetween(knotAndChain(), 0, CHAIN_END, 1.5);
+
+    expect(route).not.toBeNull();
+    expect(route!.stars[route!.stars.length - 1]).toBe(CHAIN_END);
+    expect(route!.longestHopPc).toBeLessThanOrEqual(1.5);
+  });
 });
 
+/**
+ * 45 000 stars scattered through the 30 pc cube around the origin, twenty times the density around
+ * the real Sun and more than a search's budget, with a chain a parsec a hop running along x from
+ * the origin out through the crowd and on to 75 pc — and one star at 500 pc that nothing reaches.
+ */
+const CHAIN_END = 75;
+const ISLAND = 999;
+function knotAndChain(cellSizePc?: number): StarNeighbourhood {
+  let seed = 7;
+  const random = () => ((seed = (seed * 1103515245 + 12345) % 2147483648) / 2147483648) * 30 - 15;
+  const knot: StarPoint[] = Array.from({ length: 45000 }, (_, i) => ({ id: 1000 + i, x: random(), y: random(), z: random() }));
+  const chainOut: StarPoint[] = Array.from({ length: CHAIN_END }, (_, i) => ({ id: i + 1, x: i + 1, y: 0, z: 0 }));
+  return new StarNeighbourhood([{ id: 0, x: 0, y: 0, z: 0 }, ...knot, ...chainOut, { id: ISLAND, x: 500, y: 0, z: 0 }], cellSizePc);
+}
+
+/**
+ * Exactly a search's budget of stars that reach one another — 40 000 a parsec apart along x, which
+ * a 1.5 pc range walks end to end — and one 500 pc off that line, which nothing reaches. The dead
+ * end is real and the search proves it, with the last star it is allowed.
+ *
+ * A line rather than a crowd because the count has to be exact: a random cloud dense enough to
+ * connect leaves clumps the departure never reaches, and 39 662 of 40 000 settled is a budget that
+ * was never spent.
+ */
+const BUDGET_ISLAND = 99_999;
+function budgetExactly(): StarNeighbourhood {
+  const line: StarPoint[] = Array.from({ length: 40_000 }, (_, i) => ({ id: i, x: i, y: 0, z: 0 }));
+  return new StarNeighbourhood([...line, { id: BUDGET_ISLAND, x: 0, y: 500, z: 0 }], 1.5);
+}
+
+/**
+ * 45 000 stars in a 10 pc cube — dense enough to stay one connected piece at half a parsec, where
+ * walking it costs more than a search's budget — with a chain a parsec a hop leaving its edge for
+ * 30 pc. Its cells are sized for the ranges asked of it, as the real catalogue's are for its own.
+ */
+const CROWD_CHAIN_END = 25;
+const CROWD_ISLAND = 999999;
+function crowdedKnot(): StarNeighbourhood {
+  let seed = 11;
+  const random = () => ((seed = (seed * 1103515245 + 12345) % 2147483648) / 2147483648) * 10 - 5;
+  const knot: StarPoint[] = Array.from({ length: 45000 }, (_, i) => ({ id: 1000 + i, x: random(), y: random(), z: random() }));
+  const chainOut: StarPoint[] = Array.from({ length: CROWD_CHAIN_END }, (_, i) => ({ id: i + 1, x: 5 + i + 1, y: 0, z: 0 }));
+  // One star nothing reaches, for the questions that have no answer.
+  return new StarNeighbourhood([{ id: 0, x: 0, y: 0, z: 0 }, ...knot, ...chainOut, { id: CROWD_ISLAND, x: 500, y: 0, z: 0 }], 0.25);
+}
+
 describe('minimumRangeBetween', () => {
+  it('works out the range past a dense knot around the departure', () => {
+    // Past the crowd the chain's hops of a parsec are the only way on, so a parsec is the
+    // answer, to the half-step the panel rounds up to.
+    expect(minimumRangeBetween(knotAndChain(), 0, CHAIN_END, 8).rangePc).toBeCloseTo(1, 1);
+  });
+
+  it('stops bisecting where a search gave up, and hands back a range that does work', { timeout: 30_000 }, () => {
+    // Below the chain's own hop of a parsec, the crowd is still one connected piece and larger than
+    // the budget, so those probes give up. Reading a give-up as "no chain at this range" is what
+    // used to report ranges up to 29% wider than needed, and went on paying for probes whose
+    // answers it could not use; the answer now is the narrowest range a chain was found at.
+    const knot = crowdedKnot();
+
+    const needed = minimumRangeBetween(knot, 0, CROWD_CHAIN_END, 1.2);
+
+    expect(needed.least).toBe(false);
+    expect(needed.rangePc).not.toBeNull();
+    expect(routeBetween(knot, 0, CROWD_CHAIN_END, needed.rangePc!).route).not.toBeNull();
+    // Narrower than the ceiling's own route, too: stopping before the bisection has found a range
+    // of its own hands back the ceiling, which is the control's maximum — the question, not an answer.
+    expect(needed.rangePc!).toBeLessThan(routeBetween(knot, 0, CROWD_CHAIN_END, 1.2).route!.longestHopPc);
+  });
+
   it('names the shortest range that opens a way through', () => {
     // Hops of 1 and 4: no range under 4 connects them, and 4 exactly does.
     const stepped = index([
@@ -92,9 +193,9 @@ describe('minimumRangeBetween', () => {
       { id: 2, x: 5, y: 0, z: 0 }
     ]);
 
-    expect(minimumRangeBetween(stepped, 0, 2, 50)).toBeCloseTo(4);
+    expect(minimumRangeBetween(stepped, 0, 2, 50)).toEqual({ rangePc: expect.closeTo(4) as number, least: true });
-    expect(routeBetween(stepped, 0, 2, 4)).not.toBeNull();
+    expect(routeBetween(stepped, 0, 2, 4).route).not.toBeNull();
-    expect(routeBetween(stepped, 0, 2, 3.99)).toBeNull();
+    expect(routeBetween(stepped, 0, 2, 3.99).route).toBeNull();
   });
 
   it('prefers a longer way whose worst hop is shorter, since that is what the range pays for', () => {
@@ -108,8 +209,16 @@ describe('minimumRangeBetween', () => {
 
     const needed = minimumRangeBetween(both, 0, 3, 50);
 
-    expect(needed).toBeLessThan(10);
+    expect(needed.rangePc).toBeLessThan(10);
-    expect(routeBetween(both, 0, 3, needed!)).not.toBeNull();
+    expect(routeBetween(both, 0, 3, needed.rangePc!).route).not.toBeNull();
+  });
+
+  it('claims nothing about a ceiling its own search gave up on', () => {
+    // Nothing reaches the island at any range here, but the crowd spends the budget first, so the
+    // widest search proves nothing — and neither does the null it hands back.
+    const needed = minimumRangeBetween(crowdedKnot(), 0, CROWD_ISLAND, 0.5);
+
+    expect(needed).toEqual({ rangePc: null, least: false });
   });
 
   it('finds nothing when even the ceiling does not reach', () => {
@@ -118,29 +227,138 @@ describe('minimumRangeBetween', () => {
       { id: 1, x: 100, y: 0, z: 0 }
     ]);
 
-    expect(minimumRangeBetween(split, 0, 1, 50)).toBeNull();
+    expect(minimumRangeBetween(split, 0, 1, 50)).toEqual({ rangePc: null, least: true });
   });
 });
 
-describe('collectJumpLinks', () => {
+/**
-  it('reports each pair once, not once from either end', () => {
+ * The links a segment buffer draws, as unordered pairs of star ids, read back from where each end
-    const links = collectJumpLinks(chain(4), 1.5);
+ * sits. Positions are compared as the float32 the buffer holds.
+ */
+function linksDrawn(segments: Float32Array, points: readonly StarPoint[]): string[] {
+  const idAt = new Map(points.map((point) => [[point.x, point.y, point.z].map(Math.fround).join(), point.id]));
+  const links: string[] = [];
+  for (let at = 0; at < segments.length; at += 6) {
+    const a = idAt.get(Array.from(segments.subarray(at, at + 3)).join())!;
+    const b = idAt.get(Array.from(segments.subarray(at + 3, at + 6)).join())!;
+    links.push(a < b ? `${a}-${b}` : `${b}-${a}`);
+  }
+  return links;
+}
 
-    expect(links.map((link) => [link.from, link.to])).toEqual([
+/**
-      [0, 1],
+ * What a budget should keep, worked out the slow way: every link sorted by how near its nearer end
-      [1, 2],
+ * is to the centre, then taken until one does not fit. Lengths and distances as the float32 buffer
-      [2, 3]
+ * holds them.
-    ]);
+ */
+function nearestFirst(points: readonly StarPoint[], rangePc: number, centre: { x: number; y: number; z: number }, lengthPc: number): string[] {
+  const all = jumpLinkSegments(index([...points]), rangePc);
+  const links = Array.from({ length: all.length / 6 }, (_, link) => {
+    const v = Array.from(all.subarray(link * 6, link * 6 + 6));
+    const nearer = Math.fround(Math.sqrt(Math.min((v[0] - centre.x) ** 2 + (v[1] - centre.y) ** 2 + (v[2] - centre.z) ** 2, (v[3] - centre.x) ** 2 + (v[4] - centre.y) ** 2 + (v[5] - centre.z) ** 2)));
+    return { link, nearer, length: Math.fround(Math.hypot(v[3] - v[0], v[4] - v[1], v[5] - v[2])), key: linksDrawn(all.subarray(link * 6, link * 6 + 6), points)[0] };
+  }).sort((a, b) => a.nearer - b.nearer || a.link - b.link);
+  const kept: string[] = [];
+  let total = 0;
+  for (const { length, key } of links) {
+    if (total + length > lengthPc) {
+      break;
+    }
+    total += length;
+    kept.push(key);
+  }
+  return kept;
+}
+
+/** Stars a parsec apart along x, as points, for reading a segment buffer back. */
+function chainPoints(count: number): StarPoint[] {
+  return Array.from({ length: count }, (_, i) => ({ id: i, x: i, y: 0, z: 0 }));
+}
+
+describe('jumpLinkSegments', () => {
+  it('draws each pair once, not once from either end', () => {
+    const segments = jumpLinkSegments(chain(4), 1.5);
+
+    expect(linksDrawn(segments, chainPoints(4)).sort()).toEqual(['0-1', '1-2', '2-3']);
   });
 
-  it('measures every link it reports', () => {
+  it('puts both ends of every link where its stars are', () => {
-    const links = collectJumpLinks(chain(3), 2.5);
+    const segments = jumpLinkSegments(chain(3), 2.5);
 
-    expect(links.find((link) => link.from === 0 && link.to === 2)?.distancePc).toBeCloseTo(2);
+    expect(segments).toHaveLength(3 * 6);
+    expect(linksDrawn(segments, chainPoints(3)).sort()).toEqual(['0-1', '0-2', '1-2']);
   });
 
   it('draws nothing at no range', () => {
-    expect(collectJumpLinks(chain(4), 0)).toEqual([]);
+    expect(jumpLinkSegments(chain(4), 0)).toHaveLength(0);
+  });
+
+  it('keeps the links nearest the centre first, for as much length as the budget holds', () => {
+    // A parsec apart from 0 to 20, the centre at 10.3. By nearer end: 9-10 and 10-11 (0.3 away),
+    // then 11-12 (0.7), then 8-9 (1.3). Three parsecs of them fit in 3.5; a fourth would not.
+    const budget = { centre: { x: 10.3, y: 0, z: 0 }, lengthPc: 3.5 };
+
+    const segments = jumpLinkSegments(chain(21), 1.5, budget);
+
+    expect(linksDrawn(segments, chainPoints(21)).sort()).toEqual(['10-11', '11-12', '9-10']);
+    expect(segments.buffer.byteLength).toBe(segments.byteLength);
+  });
+
+  it('keeps exactly the links a full nearest-first sort would, without sorting them all', () => {
+    let seed = 7;
+    const random = () => ((seed = (seed * 1103515245 + 12345) % 2147483648) / 2147483648) * 40 - 20;
+    const points: StarPoint[] = Array.from({ length: 600 }, (_, id) => ({ id, x: random(), y: random(), z: random() }));
+    const centre = { x: 3, y: -2, z: 1 };
+
+    for (const lengthPc of [0, 5, 60, 900, 4000, 1e9]) {
+      expect(linksDrawn(jumpLinkSegments(index(points), 4, { centre, lengthPc }), points).sort()).toEqual(nearestFirst(points, 4, centre, lengthPc).sort());
+    }
+  });
+
+  it('sorts the distance band the budget runs out in, and stops at the first link there that does not fit', () => {
+    // One pair 4 kpc out makes each band about a parsec deep, so dozens of short links near the
+    // centre share the band the budget ends in, in whatever order the grid walks them.
+    let seed = 3;
+    const random = () => (seed = (seed * 1103515245 + 12345) % 2147483648) / 2147483648;
+    const points: StarPoint[] = [{ id: 0, x: 4000, y: 0, z: 0 }, { id: 1, x: 4000.03, y: 0, z: 0 }];
+    for (let pair = 0; pair < 40; pair++) {
+      const r = 0.05 + random() * 0.9;
+      const theta = random() * Math.PI * 2;
+      const x = r * Math.cos(theta);
+      const y = r * Math.sin(theta);
+      points.push({ id: 2 + pair * 2, x, y, z: 0 }, { id: 3 + pair * 2, x, y, z: 0.005 + random() * 0.04 });
+    }
+    const centre = { x: 0, y: 0, z: 0 };
+
+    for (const lengthPc of [0.1, 0.3, 0.5]) {
+      expect(linksDrawn(jumpLinkSegments(index(points), 0.05, { centre, lengthPc }), points).sort()).toEqual(nearestFirst(points, 0.05, centre, lengthPc).sort());
+    }
+  });
+
+  it('counts the budget in parsecs of link, not in links', () => {
+    // Stars at 0, 1 and 3: a 2 pc link nearest the centre, then a 1 pc one. Two and a half parsecs
+    // hold the first and not both, though two links would fit a count of two and a half.
+    const points: StarPoint[] = [{ id: 0, x: 0, y: 0, z: 0 }, { id: 1, x: 1, y: 0, z: 0 }, { id: 2, x: 3, y: 0, z: 0 }];
+
+    const segments = jumpLinkSegments(index(points), 2.5, { centre: { x: 3, y: 0, z: 0 }, lengthPc: 2.5 });
+
+    expect(linksDrawn(segments, points)).toEqual(['1-2']);
+  });
+
+  it('grows past its first buffer without losing a link', () => {
+    // 5 000 stars a tenth of a parsec apart, ten neighbours each way in range: some 50 000 links, far past
+    // the 4 096 the buffer starts with, so it has to grow several times.
+    const count = 5000;
+    const line = new StarNeighbourhood(Array.from({ length: count }, (_, i) => ({ id: i, x: i / 10, y: 0, z: 0 })));
+    // 1.05 rather than 1: the tenth neighbour sits at 1.0, which float steps of a tenth put either side of it.
+    const segments = jumpLinkSegments(line, 1.05);
+
+    let expected = 0;
+    for (let i = 0; i < count; i++) {
+      expected += Math.min(10, count - 1 - i);
+    }
+    expect(segments.length / 6).toBe(expected);
+    expect(segments.buffer.byteLength).toBe(segments.byteLength);
   });
 
   it('agrees with every route it makes possible', () => {
@@ -154,10 +372,9 @@ describe('collectJumpLinks', () => {
     // earlier version of this test hid by only checking the route it happened to find.
     const range = 9;
 
-    const links = collectJumpLinks(cloud, range);
+    const drawn = new Set(linksDrawn(jumpLinkSegments(cloud, range), points));
-    const drawn = new Set(links.map((link) => `${link.from}-${link.to}`));
 
-    const route = routeBetween(cloud, 0, 119, range);
+    const { route } = routeBetween(cloud, 0, 119, range);
     // Asserted, not guarded: a skipped body would let the two disagree unnoticed.
     expect(route).not.toBeNull();
     expect(route!.stars.length).toBeGreaterThan(2);
@@ -165,6 +382,6 @@ describe('collectJumpLinks', () => {
       const [a, b] = [route!.stars[i - 1], route!.stars[i]].sort((x, y) => x - y);
       expect(drawn.has(`${a}-${b}`)).toBe(true);
     }
-    expect(links.length).toBeGreaterThan(0);
+    expect(drawn.size).toBeGreaterThan(0);
   });
 });

src/app/shared/astro/jump-links.ts

@@ -16,6 +16,21 @@
 
 import { StarNeighbourhood } from './star-neighbourhood';
 
+/** What a search found, and whether it looked everywhere the range reaches before answering. */
+export interface RouteSearch {
+  readonly route: Route | null;
+  /** True when the search spent its budget: "no route" then means "gave up", not "there is none". */
+  readonly gaveUp: boolean;
+}
+
+/** A range that opens a route, and whether anything shorter was actually ruled out. */
+export interface RangeSearch {
+  /** A range a chain was found at, or `null` where none was found up to the ceiling. */
+  readonly rangePc: number | null;
+  /** True when every shorter range was searched to exhaustion, so this is the least that works. */
+  readonly least: boolean;
+}
+
 /** A chain of stars from one to another, each hop within the range that was asked for. */
 export interface Route {
   /** Star ids, departure first and destination last. One hop is two ids. */
@@ -29,38 +44,96 @@ export interface Route {
   readonly longestHopPc: number;
 }
 
-/** An unordered pair of stars within range of each other. */
+/**
-export interface JumpLink {
+ * A cap on how much of the catalogue one search may walk, so a hopeless question cannot run for
-  readonly from: number;
+ * ever. It is a budget, not a verdict: a search that spends it has proved nothing, and says so
-  readonly to: number;
+ * through {@link RouteSearch.gaveUp}.
-  readonly distancePc: number;
+ *
-}
+ * Sized against the catalogue actually shipped rather than against the longest route. At 20 000 a
+ * search from the Sun to HD 120147 (136 pc) in jumps of 5 pc gave up, though the chain it wanted,
+ * 50 jumps, is there to be found; a star at 170 pc needed 58. Both are found at this budget. The
+ * cost is paid by questions with no answer, which walk the whole of it: from the Sun to the
+ * farthest star at 8 pc, 0.7 s at 20 000 against 2.1 s here, in the worker.
+ */
+const MAX_VISITED = 40000;
 
 /**
- * A cap on how much of the catalogue one search may walk. Reached only where a route does not
+ * How close to the true minimum `minimumRangeBetween` works a range out: half the Routes panel's
- * exist and the range is wide enough to make most of the catalogue one component; a search that
+ * own step, which it rounds up to. Never at the cost of an answer that fails to open a route,
- * hits it has already visited more stars than any real chain passes through.
+ * since the figure it reports is always the longest hop of a route actually found.
  */
-const MAX_VISITED = 20000;
+const RANGE_RESOLUTION_PC = 0.05;
 
-/** Pops the smallest-cost entry. A linear scan: the frontier is small next to the work per node. */
+/**
-function takeCheapest<T>(frontier: Map<number, T>, costOf: (value: T) => number): [number, T] | undefined {
+ * How many of `minimumRangeBetween`'s probes may give up, once it has a range of its own, before it
-  let bestId: number | undefined;
+ * answers with what it has — and how many before it has one.
-  let bestValue: T | undefined;
+ *
-  let bestCost = Number.POSITIVE_INFINITY;
+ * A probe that finds a route is quick — it heads straight for the destination — while one that
-  for (const [id, value] of frontier) {
+ * gives up walks the whole search budget, about two seconds on the real catalogue. Those are also
-    const cost = costOf(value);
+ * the probes that buy the least: they cannot rule anything out. Two of them is the difference
-    if (cost < bestCost) {
+ * between an answer of 7.96 pc in half a second and 5.76 pc in seventeen, for a star at 236 pc; it
-      bestCost = cost;
+ * lands on 5.97 pc in five.
-      bestId = id;
+ *
-      bestValue = value;
+ * Until a probe succeeds there is nothing to answer with but the ceiling route's own longest hop,
+ * which is the control's maximum, so the bound is looser there — but a bound, since the search is
+ * one the panel waits on: five probes, ten seconds, rather than the resolution's own eight.
+ */
+const MAX_RANGE_GIVE_UPS = 2;
+const MAX_UNEARNED_GIVE_UPS = 5;
+
+/** A binary min-heap of star ids by priority. Duplicates are allowed; stale ones are skipped on the way out. */
+class Frontier {
+  private readonly ids: number[] = [];
+  private readonly priorities: number[] = [];
+
+  get size(): number {
+    return this.ids.length;
   }
+
+  push(id: number, priority: number): void {
+    let at = this.ids.length;
+    this.ids.push(id);
+    this.priorities.push(priority);
+    while (at > 0) {
+      const parent = (at - 1) >> 1;
+      if (this.priorities[parent] <= priority) {
+        break;
       }
-  if (bestId === undefined || bestValue === undefined) {
+      this.ids[at] = this.ids[parent];
-    return undefined;
+      this.priorities[at] = this.priorities[parent];
+      at = parent;
+    }
+    this.ids[at] = id;
+    this.priorities[at] = priority;
+  }
+
+  /** The id with the lowest priority, taken out. Only called while `size` is not zero. */
+  pop(): number {
+    const top = this.ids[0];
+    const lastId = this.ids.pop()!;
+    const lastPriority = this.priorities.pop()!;
+    const count = this.ids.length;
+    if (count > 0) {
+      let at = 0;
+      for (;;) {
+        const left = 2 * at + 1;
+        if (left >= count) {
+          break;
+        }
+        const right = left + 1;
+        const child = right < count && this.priorities[right] < this.priorities[left] ? right : left;
+        if (this.priorities[child] >= lastPriority) {
+          break;
+        }
+        this.ids[at] = this.ids[child];
+        this.priorities[at] = this.priorities[child];
+        at = child;
+      }
+      this.ids[at] = lastId;
+      this.priorities[at] = lastPriority;
+    }
+    return top;
   }
-  frontier.delete(bestId);
-  return [bestId, bestValue];
 }
 
 function rebuild(cameFrom: Map<number, number>, fromId: number, toId: number): number[] {
@@ -78,129 +151,243 @@ function rebuild(cameFrom: Map<number, number>, fromId: number, toId: number): n
 }
 
 /**
- * The shortest chain from one star to another in which no single hop exceeds `rangePc`, or
+ * The shortest chain from one star to another in which no single hop exceeds `rangePc`, or no
- * `null` where the catalogue holds no such chain.
+ * chain where the catalogue holds none within the search's budget.
  *
  * Shortest by total distance travelled rather than by number of hops: two chains of the same
  * length are not equally good, and the one that covers less ground is the one a reader means by
  * "the way there". Neighbours are asked for as the search reaches each star rather than built
  * into a graph first, so finding one route never costs a pass over the whole catalogue.
+ *
+ * An A* search: each star waits its turn by the distance travelled to it plus the straight line
+ * on to the destination, which no chain can beat, so the search heads for the destination rather
+ * than widening evenly in every direction. Widening evenly is what the Gaia catalogue broke. From
+ * the Sun it spent its whole budget on the 20 000 stars nearest, all inside about 40 pc, and so
+ * found no route to anything farther at any range; Mirfak, 155 pc out, is 27 jumps at 8 pc.
+ *
+ * "No route" and "no chain" are not the same answer: a search that spends {@link MAX_VISITED}
+ * reports that it gave up, so nothing downstream reads it as proof that no chain exists.
  */
-export function routeBetween(index: StarNeighbourhood, fromId: number, toId: number, rangePc: number): Route | null {
+export function routeBetween(index: StarNeighbourhood, fromId: number, toId: number, rangePc: number): RouteSearch {
-  if (fromId === toId || rangePc <= 0 || !index.point(fromId) || !index.point(toId)) {
+  const origin = index.point(fromId);
-    return null;
+  const destination = index.point(toId);
+  if (fromId === toId || rangePc <= 0 || !origin || !destination) {
+    return { route: null, gaveUp: false };
   }
+  const straightLineOn = (x: number, y: number, z: number) => Math.hypot(destination.x - x, destination.y - y, destination.z - z);
 
-  const best = new Map<number, number>([[fromId, 0]]);
+  const travelled = new Map<number, number>([[fromId, 0]]);
   const cameFrom = new Map<number, number>();
+  // Each hop's length as the range test measured it. The route's longest hop is read from these
+  // rather than measured again, so a range set to it is sure to admit the route a second time,
+  // which is what `minimumRangeBetween` relies on.
+  const hopTo = new Map<number, number>();
   const settled = new Set<number>();
-  const frontier = new Map<number, number>([[fromId, 0]]);
+  const frontier = new Frontier();
+  frontier.push(fromId, straightLineOn(origin.x, origin.y, origin.z));
 
-  while (frontier.size > 0 && settled.size < MAX_VISITED) {
+  let gaveUp = false;
-    const cheapest = takeCheapest(frontier, (cost) => cost);
+  while (frontier.size > 0) {
-    if (!cheapest) {
+    const starId = frontier.pop();
-      break;
-    }
-    const [starId, costHere] = cheapest;
     if (settled.has(starId)) {
       continue;
     }
+    // Counted against the budget only once the frontier has been drained of stale duplicates, so
+    // the flag below records why the search stopped rather than how full the set happened to be.
+    if (settled.size >= MAX_VISITED) {
+      gaveUp = true;
+      break;
+    }
     settled.add(starId);
+    const costHere = travelled.get(starId)!;
 
     if (starId === toId) {
       const stars = rebuild(cameFrom, fromId, toId);
-      return stars.length === 0 ? null : { stars, totalPc: costHere, longestHopPc: longestHop(index, stars) };
+      if (stars.length === 0) {
+        return { route: null, gaveUp: false };
       }
-
+      let longestHopPc = 0;
-    for (const neighbour of index.within(starId, rangePc)) {
-      if (settled.has(neighbour.id)) {
-        continue;
-      }
-      const cost = costHere + neighbour.distancePc;
-      if (cost < (best.get(neighbour.id) ?? Number.POSITIVE_INFINITY)) {
-        best.set(neighbour.id, cost);
-        cameFrom.set(neighbour.id, starId);
-        frontier.set(neighbour.id, cost);
-      }
-    }
-  }
-
-  return null;
-}
-
-function longestHop(index: StarNeighbourhood, stars: readonly number[]): number {
-  let longest = 0;
       for (let i = 1; i < stars.length; i++) {
-    const a = index.point(stars[i - 1]);
+        longestHopPc = Math.max(longestHopPc, hopTo.get(stars[i])!);
-    const b = index.point(stars[i]);
-    if (a && b) {
-      longest = Math.max(longest, Math.hypot(b.x - a.x, b.y - a.y, b.z - a.z));
       }
+      return { route: { stars, totalPc: costHere, longestHopPc }, gaveUp: false };
     }
-  return longest;
+
+    index.forEachWithin(starId, rangePc, (neighbour, distancePc) => {
+      if (settled.has(neighbour.id)) {
+        return;
+      }
+      const cost = costHere + distancePc;
+      if (cost < (travelled.get(neighbour.id) ?? Number.POSITIVE_INFINITY)) {
+        travelled.set(neighbour.id, cost);
+        cameFrom.set(neighbour.id, starId);
+        hopTo.set(neighbour.id, distancePc);
+        frontier.push(neighbour.id, cost + straightLineOn(neighbour.x, neighbour.y, neighbour.z));
+      }
+    });
+  }
+
+  // An empty frontier means the range reaches nothing further; a spent budget means only that the
+  // search stopped looking.
+  return { route: null, gaveUp };
 }
 
 /**
- * The shortest range at which any chain at all exists between two stars, or `null` if none does
+ * A range at which a chain exists between two stars — the shortest, to within
- * within `ceilingPc`.
+ * `RANGE_RESOLUTION_PC`, where every shorter range could be ruled out — or `null` where no chain
+ * was found up to `ceilingPc`.
  *
- * This is what turns "no route" from a dead end into an answer: the range control can be told
+ * This is what turns "no route" from a dead end into an answer: the range control can be told what
- * what it would have to be raised to. It is the minimax path — the chain whose longest hop is as
+ * it would have to be raised to. The figure aimed at is the minimax path, the chain whose longest
- * short as possible — found by the same search as above, with the cost of reaching a star being
+ * hop is as short as possible. It used to be searched for directly, widening from the departure in
- * the longest hop taken to get there rather than the sum of them.
+ * order of the worst hop needed, which from the Sun meant exhausting the whole dense core before
+ * anything farther could be reached: it gave up with nothing after up to a minute. Whether a chain
+ * exists can only become truer as the range grows, so the range is bisected instead, each step one
+ * directed `routeBetween`.
+ *
+ * Each step has to answer "is there a chain at this range", and a search that gives up answers
+ * nothing. It is still worth carrying on from — the ranges above it are the ones left to try — but
+ * the result is no longer the least range, only a range that works, and `least` says which. The
+ * number of steps that may give up is bounded for the same reason: each one walks the whole budget,
+ * and 11 s of them for a star at 236 pc bought two decimal places nobody reads. Bounded more
+ * loosely before the bisection has found a range of its own, since until then the only range it
+ * could offer is the ceiling's, which is the control's maximum, for crossings that work well below
+ * it. See {@link MAX_RANGE_GIVE_UPS}.
  */
-export function minimumRangeBetween(index: StarNeighbourhood, fromId: number, toId: number, ceilingPc: number): number | null {
+export function minimumRangeBetween(index: StarNeighbourhood, fromId: number, toId: number, ceilingPc: number): RangeSearch {
-  if (fromId === toId || ceilingPc <= 0 || !index.point(fromId) || !index.point(toId)) {
+  const widest = routeBetween(index, fromId, toId, ceilingPc);
-    return null;
+  if (!widest.route) {
+    return { rangePc: null, least: !widest.gaveUp };
+  }
+  const ceilingHopPc = widest.route.longestHopPc;
+  let unreachable = 0;
+  let reachable = ceilingHopPc;
+  let giveUps = 0;
+  // While `reachable` is still the ceiling route's own longest hop the bisection has nothing of its
+  // own to answer with, and that figure sends the control to its maximum for a crossing that works
+  // well below — 8.00 pc for a star that routes at 6. So it is allowed more probes there, not
+  // unlimited ones: the panel is waiting on this.
+  while (reachable - unreachable > RANGE_RESOLUTION_PC && giveUps < (reachable === ceilingHopPc ? MAX_UNEARNED_GIVE_UPS : MAX_RANGE_GIVE_UPS)) {
+    const range = (unreachable + reachable) / 2;
+    const { route, gaveUp } = routeBetween(index, fromId, toId, range);
+    if (route) {
+      reachable = route.longestHopPc;
+    } else {
+      // A search that gave up is worth going on from — the ranges above it are the ones left to
+      // try — but it is not evidence that nothing routes here, so the answer stops being the least.
+      unreachable = range;
+      giveUps += gaveUp ? 1 : 0;
+    }
+  }
+  // Without a give-up the loop can only have ended by closing on the resolution, so that is the least.
+  return { rangePc: reachable, least: giveUps === 0 };
+}
+
+/** How much of a graph to keep: the links nearest a point, up to a total length. */
+export interface LinkBudget {
+  /** Links are kept in order of how near their nearer end is to this point. */
+  readonly centre: { readonly x: number; readonly y: number; readonly z: number };
+  /** The most the kept links may add up to, end to end, in parsecs. */
+  readonly lengthPc: number;
+}
+
+/**
+ * How many distance bands a budgeted graph is split into to find where its budget runs out, so that
+ * only the links in that one band are sorted rather than all of them.
+ */
+const DISTANCE_BANDS = 4096;
+
+/**
+ * Every link within `rangePc` between two of the stars `index` holds, each pair once, as vertex
+ * pairs ready to draw: six floats a link, one end then the other. With a `budget`, only the links
+ * nearest its centre, as many as fit its length.
+ *
+ * For drawing the graph, which is the only thing that wants all of it: routing asks for a star's
+ * neighbours as it reaches that star and never builds this. Written straight into floats rather
+ * than collected as link objects first, since at 8 pc the drawn stars alone have hundreds of
+ * thousands of links, and the whole catalogue 3.7 million.
+ */
+export function jumpLinkSegments(index: StarNeighbourhood, rangePc: number, budget?: LinkBudget): Float32Array {
+  let vertices = new Float32Array(6 * 4096);
+  let length = 0;
+  index.forEachPairWithin(rangePc, (a, b) => {
+    if (length + 6 > vertices.length) {
+      const grown = new Float32Array(vertices.length * 2);
+      grown.set(vertices);
+      vertices = grown;
+    }
+    vertices[length++] = a.x;
+    vertices[length++] = a.y;
+    vertices[length++] = a.z;
+    vertices[length++] = b.x;
+    vertices[length++] = b.y;
+    vertices[length++] = b.z;
+  });
+  if (!budget) {
+    // Exact length rather than a view on the grown buffer: the answer is transferred whole, and a
+    // view would carry up to as much again in unused capacity with it.
+    return vertices.slice(0, length);
   }
 
-  const best = new Map<number, number>([[fromId, 0]]);
+  // Each link's nearer end's distance from the centre, and its length.
-  const settled = new Set<number>();
+  const { centre } = budget;
-  const frontier = new Map<number, number>([[fromId, 0]]);
+  const count = length / 6;
+  const nearness = new Float32Array(count);
+  const lengths = new Float32Array(count);
+  let totalPc = 0;
+  let farthest = 0;
+  for (let link = 0; link < count; link++) {
+    const at = link * 6;
+    const ax = vertices[at] - centre.x;
+    const ay = vertices[at + 1] - centre.y;
+    const az = vertices[at + 2] - centre.z;
+    const bx = vertices[at + 3] - centre.x;
+    const by = vertices[at + 4] - centre.y;
+    const bz = vertices[at + 5] - centre.z;
+    nearness[link] = Math.sqrt(Math.min(ax * ax + ay * ay + az * az, bx * bx + by * by + bz * bz));
+    lengths[link] = Math.hypot(bx - ax, by - ay, bz - az);
+    totalPc += lengths[link];
+    farthest = Math.max(farthest, nearness[link]);
+  }
+  if (totalPc <= budget.lengthPc) {
+    return vertices.slice(0, length);
+  }
 
-  while (frontier.size > 0 && settled.size < MAX_VISITED) {
+  // Nearest first, without sorting them all: every link in the bands before the one where the budget
-    const cheapest = takeCheapest(frontier, (cost) => cost);
+  // runs out fits, and only that band's links are sorted to see how many of them do. Sorting all
-    if (!cheapest) {
+  // 730 000 links at 30 pc from the Sun to keep 4 400 doubled the time a graph took in the worker.
+  const bands = new Uint16Array(count);
+  const bandLengths = new Float64Array(DISTANCE_BANDS);
+  const bandsPerPc = farthest > 0 ? DISTANCE_BANDS / farthest : 0;
+  for (let link = 0; link < count; link++) {
+    bands[link] = Math.min(DISTANCE_BANDS - 1, Math.floor(nearness[link] * bandsPerPc));
+    bandLengths[bands[link]] += lengths[link];
+  }
+  let lastBand = 0;
+  let keptPc = 0;
+  while (keptPc + bandLengths[lastBand] <= budget.lengthPc) {
+    keptPc += bandLengths[lastBand++];
+  }
+  const keptLinks: number[] = [];
+  const boundary: number[] = [];
+  for (let link = 0; link < count; link++) {
+    const band = bands[link];
+    if (band < lastBand) {
+      keptLinks.push(link);
+    } else if (band === lastBand) {
+      boundary.push(link);
+    }
+  }
+  boundary.sort((a, b) => nearness[a] - nearness[b] || a - b);
+  for (const link of boundary) {
+    if (keptPc + lengths[link] > budget.lengthPc) {
       break;
     }
-    const [starId, worstHopHere] = cheapest;
+    keptPc += lengths[link];
-    if (settled.has(starId)) {
+    keptLinks.push(link);
-      continue;
-    }
-    settled.add(starId);
-
-    if (starId === toId) {
-      return worstHopHere;
   }
 
-    for (const neighbour of index.within(starId, ceilingPc)) {
+  const kept = new Float32Array(keptLinks.length * 6);
-      if (settled.has(neighbour.id)) {
+  keptLinks.forEach((link, at) => kept.set(vertices.subarray(link * 6, link * 6 + 6), at * 6));
-        continue;
+  return kept;
-      }
-      // What this chain would need: the longest hop on it, not the distance covered by it.
-      const needed = Math.max(worstHopHere, neighbour.distancePc);
-      if (needed < (best.get(neighbour.id) ?? Number.POSITIVE_INFINITY)) {
-        best.set(neighbour.id, needed);
-        frontier.set(neighbour.id, needed);
-      }
-    }
-  }
-
-  return null;
-}
-
-/**
- * Every link within `rangePc` in the whole catalogue, each pair once.
- *
- * For drawing the graph, which is the only thing that wants all of it: routing asks for a
- * star's neighbours as it reaches that star and never builds this.
- */
-export function collectJumpLinks(index: StarNeighbourhood, rangePc: number): JumpLink[] {
-  const links: JumpLink[] = [];
-  index.forEachPairWithin(rangePc, (a, b, distancePc) => {
-    // The smaller id first, always. The grid hands pairs over in whatever order it walks its
-    // cells, and a link that is `3-7` here and `7-3` there is two links to anything comparing.
-    links.push(a.id < b.id ? { from: a.id, to: b.id, distancePc } : { from: b.id, to: a.id, distancePc });
-  });
-  return links;
 }

src/app/shared/astro/routing.spec.ts

@@ -0,0 +1,112 @@
+import { describe, expect, it } from 'vitest';
+
+import { jumpLinkSegments, minimumRangeBetween, routeBetween } from './jump-links';
+import { answerRouting, indexCatalogue } from './routing';
+import { StarNeighbourhood, StarPoint } from './star-neighbourhood';
+
+/** Stars a parsec apart along x, then a gap of 5 pc to one more. */
+const POINTS = [...Array.from({ length: 5 }, (_, i) => ({ id: 10 + i, x: i, y: 0, z: 0 })), { id: 99, x: 9, y: 0, z: 0 }];
+
+function catalogue() {
+  return {
+    kind: 'catalogue' as const,
+    ids: Int32Array.from(POINTS, (point) => point.id),
+    positions: Float32Array.from(POINTS.flatMap((point) => [point.x, point.y, point.z]))
+  };
+}
+
+describe('indexCatalogue', () => {
+  it('indexes the catalogue as it was packed, id by id', () => {
+    const index = indexCatalogue(catalogue());
+
+    for (const point of POINTS) {
+      expect(index.point(point.id)).toEqual(point);
+    }
+  });
+});
+
+/** The same index, counting the neighbour queries a search makes through it. */
+class CountingNeighbourhood extends StarNeighbourhood {
+  queries = 0;
+
+  override forEachWithin(id: number, radiusPc: number, visit: (neighbour: StarPoint, distancePc: number) => void): void {
+    this.queries++;
+    super.forEachWithin(id, radiusPc, visit);
+  }
+}
+
+describe('answerRouting', () => {
+  const index = indexCatalogue(catalogue());
+  const direct = new StarNeighbourhood(POINTS);
+
+  it('answers a route the range allows, with nothing to raise it to', () => {
+    const answer = answerRouting(index, { kind: 'route', requestId: 7, fromId: 10, toId: 14, rangePc: 1.5, ceilingPc: 8 });
+
+    expect(answer).toEqual({ kind: 'route', requestId: 7, route: routeBetween(direct, 10, 14, 1.5).route, neededRangePc: null, gaveUp: false, least: true });
+  });
+
+  it('answers a route the range does not allow with the range that would', () => {
+    const answer = answerRouting(index, { kind: 'route', requestId: 8, fromId: 10, toId: 99, rangePc: 1.5, ceilingPc: 8 });
+
+    expect(answer).toEqual({ kind: 'route', requestId: 8, route: null, neededRangePc: minimumRangeBetween(direct, 10, 99, 8).rangePc, gaveUp: false, least: true });
+    expect(answer.kind === 'route' && answer.neededRangePc).toBeCloseTo(5, 1);
+  });
+
+  it('passes on that the search gave up, rather than reporting no route', () => {
+    // A crowd larger than a search's budget around the departure, and a destination nothing reaches:
+    // the answer is "it gave up", and the scene has to be able to tell that from "there is none".
+    let seed = 5;
+    const random = () => ((seed = (seed * 1103515245 + 12345) % 2147483648) / 2147483648) * 10 - 5;
+    const crowd: StarPoint[] = Array.from({ length: 45000 }, (_, i) => ({ id: 1000 + i, x: random(), y: random(), z: random() }));
+    const knot = new StarNeighbourhood([{ id: 0, x: 0, y: 0, z: 0 }, ...crowd, { id: 99, x: 500, y: 0, z: 0 }], 0.5);
+
+    const answer = answerRouting(knot, { kind: 'route', requestId: 12, fromId: 0, toId: 99, rangePc: 0.5, ceilingPc: 0.5 });
+
+    expect(answer).toMatchObject({ route: null, neededRangePc: null, gaveUp: true });
+  });
+
+  it('asks the ceiling its question once, rather than searching it again to answer it', () => {
+    // At the panel's widest range the refused route and the range search are the same question, run
+    // with the same arguments over the same index: the second pays the whole budget for the answer
+    // the first already gave.
+    const counting = new CountingNeighbourhood(POINTS);
+    const oneSearch = new CountingNeighbourhood(POINTS);
+    routeBetween(oneSearch, 10, 99, 3);
+
+    const answer = answerRouting(counting, { kind: 'route', requestId: 11, fromId: 10, toId: 99, rangePc: 3, ceilingPc: 3 });
+
+    expect(answer).toMatchObject({ route: null, neededRangePc: null });
+    expect(counting.queries).toBe(oneSearch.queries);
+  });
+
+  it('offers nothing to raise to when even the ceiling does not reach', () => {
+    const answer = answerRouting(index, { kind: 'route', requestId: 9, fromId: 10, toId: 99, rangePc: 1.5, ceilingPc: 3 });
+
+    expect(answer).toMatchObject({ route: null, neededRangePc: null });
+  });
+
+  it('answers the graph as the segments it draws', () => {
+    const answer = answerRouting(index, { kind: 'links', requestId: 3, rangePc: 1.5, drawn: Uint32Array.from(POINTS.keys()) });
+
+    expect(answer.kind).toBe('links');
+    expect(answer.requestId).toBe(3);
+    expect(answer.kind === 'links' && linkEnds(answer.segments)).toEqual(linkEnds(jumpLinkSegments(direct, 1.5)));
+  });
+
+  it('links only the drawn stars, including a pair exactly the range apart', () => {
+    // Stars at x = 0, 1, 2 and 4 drawn; the one at 3, which would bridge 2 and 4, is not. At 1 pc
+    // every link is exactly the range long, and the cells are exactly the range wide.
+    const answer = answerRouting(index, { kind: 'links', requestId: 4, rangePc: 1, drawn: Uint32Array.of(0, 1, 2, 4) });
+
+    expect(answer.kind === 'links' && linkEnds(answer.segments)).toEqual(['0-1', '1-2']);
+  });
+});
+
+/** Each link as its two ends' x, lower first, in order: the pairs, whatever order they were walked in. */
+function linkEnds(segments: Float32Array): string[] {
+  const ends: string[] = [];
+  for (let at = 0; at < segments.length; at += 6) {
+    ends.push([segments[at], segments[at + 3]].sort((a, b) => a - b).join('-'));
+  }
+  return ends.sort();
+}

src/app/shared/astro/routing.ts

@@ -0,0 +1,74 @@
+/**
+ * The route questions the map asks of the whole catalogue, as messages: what a worker is sent,
+ * what it sends back, and the one function that turns the first into the second.
+ *
+ * Kept apart from the worker itself so it runs the same on either side of the thread boundary.
+ * The scene asks through `RoutingClient`, which hands these to a Web Worker where one exists and
+ * answers them in place where one does not.
+ */
+
+import { jumpLinkSegments, LinkBudget, minimumRangeBetween, Route, routeBetween } from './jump-links';
+import { StarNeighbourhood } from './star-neighbourhood';
+
+/** The catalogue, sent once: ids, and positions packed three to a star in the same order. */
+export interface RoutingCatalogue {
+  readonly kind: 'catalogue';
+  readonly ids: Int32Array;
+  readonly positions: Float32Array;
+}
+
+export type RoutingRequest =
+  | { readonly kind: 'route'; readonly requestId: number; readonly fromId: number; readonly toId: number; readonly rangePc: number; readonly ceilingPc: number }
+  /**
+   * `drawn` is the stars the map is drawing, as positions in the catalogue that was sent: only they
+   * are linked. `budget`, where given, keeps only the links nearest the view that fit its length.
+   */
+  | { readonly kind: 'links'; readonly requestId: number; readonly rangePc: number; readonly drawn: Uint32Array; readonly budget?: LinkBudget };
+
+export type RoutingResponse =
+  /**
+   * Two searches, and two things they can fail to prove, kept apart because they are printed as
+   * different sentences. `gaveUp` is about the range that was asked for: true when that search
+   * spent its budget rather than looking everywhere the range reaches. `least` is about the search
+   * for a range that would work: true when it looked everywhere up to the ceiling, so `null` there
+   * means no chain exists rather than none was found.
+   */
+  | {
+      readonly kind: 'route';
+      readonly requestId: number;
+      readonly route: Route | null;
+      readonly neededRangePc: number | null;
+      readonly gaveUp: boolean;
+      readonly least: boolean;
+    }
+  | { readonly kind: 'links'; readonly requestId: number; readonly segments: Float32Array }
+  /** The question threw in the worker. Sent back so the request settles instead of waiting for good. */
+  | { readonly kind: 'failed'; readonly requestId: number; readonly message: string };
+
+/** A spatial index over a catalogue sent as a {@link RoutingCatalogue}. */
+export function indexCatalogue({ ids, positions }: RoutingCatalogue): StarNeighbourhood {
+  return new StarNeighbourhood(Array.from(ids, (id, i) => ({ id, x: positions[i * 3], y: positions[i * 3 + 1], z: positions[i * 3 + 2] })));
+}
+
+/**
+ * Answers one request. A route that cannot be made comes back with the range that would make one,
+ * searched no wider than `ceilingPc`, so a refusal is usually also an offer — unless the searches
+ * gave up, which is reported rather than passed off as "there is no route".
+ */
+export function answerRouting(index: StarNeighbourhood, request: RoutingRequest): RoutingResponse {
+  if (request.kind === 'links') {
+    // An index of its own over the drawn stars, in cells as wide as the range, so each cell is
+    // paired with its immediate neighbours only: 14 cells a cell at 8 pc rather than 63.
+    const drawn = new StarNeighbourhood(Array.from(request.drawn, (at) => index.pointAt(at)), request.rangePc);
+    return { kind: 'links', requestId: request.requestId, segments: jumpLinkSegments(drawn, request.rangePc, request.budget) };
+  }
+  const { route, gaveUp } = routeBetween(index, request.fromId, request.toId, request.rangePc);
+  // At the ceiling the question has just been asked: the range search would repeat it, identically
+  // and at the same cost, before bisecting below it.
+  if (route || request.rangePc >= request.ceilingPc) {
+    // Asked at the ceiling, the one search answers both questions.
+    return { kind: 'route', requestId: request.requestId, route, neededRangePc: null, gaveUp: !route && gaveUp, least: !gaveUp };
+  }
+  const needed = minimumRangeBetween(index, request.fromId, request.toId, request.ceilingPc);
+  return { kind: 'route', requestId: request.requestId, route: null, neededRangePc: needed.rangePc, gaveUp, least: needed.least };
+}

src/app/shared/astro/routing.worker.ts

@@ -0,0 +1,26 @@
+/// <reference lib="webworker" />
+
+import { answerRouting, indexCatalogue, RoutingCatalogue, RoutingRequest } from './routing';
+import { StarNeighbourhood } from './star-neighbourhood';
+
+/**
+ * Walks routes and builds the jump-link graph off the main thread. A search to a star 236 pc
+ * away, and the range it would need when there is none, can take seconds; a graph of the drawn
+ * stars at 8 pc is hundreds of thousands of links. On the page's own thread either stops the map
+ * for as long as it runs.
+ */
+let index: StarNeighbourhood | undefined;
+
+addEventListener('message', ({ data }: MessageEvent<RoutingCatalogue | RoutingRequest>) => {
+  if (data.kind === 'catalogue') {
+    index = indexCatalogue(data);
+    return;
+  }
+  // The catalogue is always the first message, and a worker's messages arrive in order.
+  try {
+    const response = answerRouting(index!, data);
+    postMessage(response, response.kind === 'links' ? [response.segments.buffer] : []);
+  } catch (error) {
+    postMessage({ kind: 'failed', requestId: data.requestId, message: error instanceof Error ? error.message : String(error) });
+  }
+});

src/app/shared/astro/star-merge.spec.ts

@@ -2,7 +2,7 @@ import { describe, expect, it } from 'vitest';
 
 import { raDegDecDistanceToXyz } from './coordinates';
 import { StarRecord } from '../models/star.model';
-import { directionCosine, isSameStar, mergeStarCatalogues } from './star-merge';
+import { directionCosine, isSameStar, MERGE_ANGULAR_TOLERANCE_DEG, mergeStarCatalogues, placementDistancePc } from './star-merge';
 
 /** A star at a given sky position and distance, which is how catalogues actually report them. */
 function at(id: number, raDeg: number, decDeg: number, distancePc: number, overrides: Partial<StarRecord> = {}): StarRecord {
@@ -13,24 +13,70 @@ function at(id: number, raDeg: number, decDeg: number, distancePc: number, overr
 const HIPPARCOS = { sourceId: 'hyg', parallaxPrecisionMas: 1 };
 const GAIA = { sourceId: 'gaia', parallaxPrecisionMas: 0.02 };
 
+/** Degrees of right ascension that span `arcsec` on the sky at declination `decDeg`. */
+function arcsecOfRa(arcsec: number, decDeg: number): number {
+  return arcsec / 3600 / Math.cos((decDeg * Math.PI) / 180);
+}
+
 describe('isSameStar', () => {
   it('matches two catalogues reporting the same star', () => {
     expect(isSameStar(at(1, 101.28, -16.71, 2.64), at(2, 101.28, -16.71, 2.63))).toBe(true);
   });
 
+  it('matches within the angular tolerance and not beyond it', () => {
+    const toleranceArcsec = MERGE_ANGULAR_TOLERANCE_DEG * 3600;
+    expect(isSameStar(at(1, 200, 10, 100), at(2, 200 + arcsecOfRa(0.9 * toleranceArcsec, 10), 10, 100))).toBe(true);
+    expect(isSameStar(at(1, 200, 10, 100), at(2, 200 + arcsecOfRa(1.1 * toleranceArcsec, 10), 10, 100))).toBe(false);
+  });
+
   it('tolerates the distance disagreement two parallaxes actually have', () => {
     // Hipparcos and Gaia routinely differ by tens of per cent at a few hundred parsecs. That
     // disagreement is the reason to prefer one of them, not evidence they are different stars.
     expect(isSameStar(at(1, 200, 10, 200), at(2, 200, 10, 260))).toBe(true);
   });
 
+  it('keeps a bright primary out of the entry of its faint companion', () => {
+    // Gaia has no Sirius — it saturates — but has Sirius B, 6″ away at the same distance and ten
+    // magnitudes fainter. Direction and distance say "same star"; the brightness says otherwise.
+    const siriusB = at(1, 101.2875, -16.7161, 2.67, { name: 'Gaia DR3 2947050466531873024', magnitude: 8.5, source: 'gaia' });
+    const sirius = at(32263, 101.2875 + arcsecOfRa(6.1, -16.7161), -16.7161, 2.637, { name: 'Sirius', magnitude: -1.44 });
+    expect(isSameStar(siriusB, sirius)).toBe(false);
+    expect(isSameStar(siriusB, { ...sirius, magnitude: 8.6 })).toBe(true);
+  });
+
+  it('lets the folded entry be fainter, as a red star is in V, but not much brighter', () => {
+    // Wolf 359 is V 13.45 in HYG and G 11.0 in Gaia — the same star, 5″ apart on a Gliese
+    // position. Almach is V 2.1 and sits 10″ from γ² And, G 4.9: Gaia has no Almach, and its
+    // name must not land on the companion.
+    const wolf359 = at(1, 164.1, 7.0, 2.41, { name: 'Gaia DR3 3864972938605115520', magnitude: 11.0, source: 'gaia' });
+    expect(isSameStar(wolf359, at(118720, 164.1 + arcsecOfRa(5, 7), 7.0, 2.39, { name: 'Wolf 359', magnitude: 13.45 }))).toBe(true);
+    const gamma2And = at(2, 30.97, 42.33, 50, { name: 'Gaia DR3 346231302441905920', magnitude: 4.9, source: 'gaia' });
+    expect(isSameStar(gamma2And, at(9640, 30.97 + arcsecOfRa(9.9, 42.33), 42.33, 50, { name: 'Almach', magnitude: 2.1 }))).toBe(false);
+  });
+
   it('does not match two different stars that happen to be at the same distance', () => {
     expect(isSameStar(at(1, 200, 10, 200), at(2, 200.5, 10, 200))).toBe(false);
   });
 
-  it('does not match along a line of sight when the distances genuinely conflict', () => {
+  it('takes two entries within three arcseconds for one star, whatever their distances say', () => {
-    // Same direction, one three times further away: a background star, not the same object.
+    // HD 225021: 143.7 pc by its Hipparcos parallax, 239.4 by Gaia's, 0.01″ apart; HIP 82724:
-    expect(isSameStar(at(1, 200, 10, 100), at(2, 200, 10, 300))).toBe(false);
+    // 3.7 pc by Hipparcos, 62.8 by Gaia, 2.3″ apart. A coincidence of direction that close is
+    // never chance at this depth; the parallax is what is wrong.
+    const gaia = at(1, 1.72, -8.9, 239.4, { name: 'Gaia DR3 395581679270412160', source: 'gaia' });
+    expect(isSameStar(gaia, at(213, 1.72 + arcsecOfRa(0.1, -8.9), -8.9, 143.7, { name: 'HD 225021' }))).toBe(true);
+    expect(isSameStar(at(2, 253.6, -38.1, 62.8, { source: 'gaia' }), at(82724, 253.6 + arcsecOfRa(2.3, -38.1), -38.1, 3.7))).toBe(true);
+  });
+
+  it('past those three arcseconds, does not match along a line of sight when the distances conflict', () => {
+    // Nearly the same direction, one three times further away: a background star, not the same object.
+    expect(isSameStar(at(1, 200, 10, 100), at(2, 200 + arcsecOfRa(5, 10), 10, 300))).toBe(false);
+  });
+
+  it('still hears the brightness inside those three arcseconds', () => {
+    // Ashlesha (ε Hya, V 3.38) has a companion 2.7″ away that Gaia does carry, three magnitudes
+    // fainter, while it does not carry Ashlesha. Direction alone would put the name on the companion.
+    const companion = at(1, 131.69, 6.42, 40, { name: 'Gaia DR3 1', magnitude: 6.7, source: 'gaia' });
+    expect(isSameStar(companion, at(43109, 131.69 + arcsecOfRa(2.7, 6.42), 6.42, 40, { name: 'Ashlesha', magnitude: 3.38 }))).toBe(false);
   });
 
   it('matches on direction rather than on 3D proximity', () => {
@@ -72,6 +118,44 @@ describe('mergeStarCatalogues', () => {
     expect(summary.duplicates).toBe(1);
   });
 
+  it('gives a matched star the better position and the name somebody gave it', () => {
+    // What a merge is for: Gaia knows where Proxima is to a fraction of a milliarcsecond and
+    // calls it by a nineteen-digit number; HYG knows its name, its spectral type and its V
+    // magnitude. Keeping one row whole loses half of that either way. The id follows the
+    // description, so a star HYG knows keeps its HYG id from one refresh to the next.
+    const hyg = at(70666, 217.4289, -62.6795, 1.2959, { name: 'Proxima Centauri', spectralType: 'M5Ve', magnitude: 11.01, colorIndex: 1.807 });
+    const gaia = at(1000064182, 217.4289, -62.6795, 1.302, { name: 'Gaia DR3 5853498713190525696', spectralType: 'Unknown', magnitude: 8.985, colorIndex: 3.805, source: 'gaia' });
+    const { stars, summary } = mergeStarCatalogues([{ ...HIPPARCOS, stars: [hyg] }, { ...GAIA, stars: [gaia] }]);
+
+    expect(stars).toEqual([{ ...hyg, x: gaia.x, y: gaia.y, z: gaia.z, source: 'gaia' }]);
+    expect(summary.duplicates).toBe(1);
+  });
+
+  it('keeps two entries of one source apart, however close they are', () => {
+    // Gaia resolves doubles Hipparcos saw as one star: two source ids 0.8″ apart are two stars,
+    // and only *another* catalogue can claim to have already listed either of them.
+    const { stars, summary } = mergeStarCatalogues([{ ...GAIA, stars: [at(1, 10, 10, 100), at(2, 10 + arcsecOfRa(0.8, 10), 10, 100)] }]);
+    expect(stars).toHaveLength(2);
+    expect(summary.duplicates).toBe(0);
+  });
+
+  it('folds an entry into the nearest match, and into each match once', () => {
+    // Gliese lists both components of a double; Gaia resolves them 0.8″ apart. Each HYG
+    // component must land on its own Gaia counterpart — not both on whichever the grid yields
+    // first, and not both on the same one.
+    const gaiaA = at(1, 10, 10, 2.68, { name: 'Gaia DR3 1', source: 'gaia' });
+    const gaiaB = at(2, 10 + arcsecOfRa(0.8, 10), 10, 2.68, { name: 'Gaia DR3 2', source: 'gaia' });
+    const a = at(118079, 10, 10, 2.63, { name: 'Gl 65A' });
+    const b = at(118080, 10 + arcsecOfRa(0.8, 10), 10, 2.63, { name: 'Gl 65B' });
+    const position = (star: StarRecord) => [star.x, star.y, star.z];
+
+    const nearest = mergeStarCatalogues([{ ...HIPPARCOS, stars: [b, a] }, { ...GAIA, stars: [gaiaA, gaiaB] }]);
+    expect(nearest.stars.map((star) => [star.name, ...position(star)])).toEqual([['Gl 65A', ...position(gaiaA)], ['Gl 65B', ...position(gaiaB)]]);
+
+    const onePlace = mergeStarCatalogues([{ ...HIPPARCOS, stars: [a, { ...b, x: a.x, y: a.y, z: a.z }] }, { ...GAIA, stars: [gaiaA, gaiaB] }]);
+    expect(onePlace.stars.map((star) => [star.name, ...position(star)])).toEqual([['Gl 65A', ...position(gaiaA)], ['Gl 65B', ...position(gaiaB)]]);
+  });
+
   it('keeps a star the better catalogue does not reach', () => {
     // The point of merging rather than replacing: Gaia is more precise but not a superset of
     // everything, and a bright star it omits should not vanish from the map.
@@ -123,6 +207,13 @@ describe('mergeStarCatalogues', () => {
       ]);
       expect(stars).toHaveLength(1);
     }
+
+    // And the one edge the grid has to wrap: 3.6″ apart, either side of 0h.
+    const { stars } = mergeStarCatalogues([
+      { ...HIPPARCOS, stars: [at(1, 359.9995, 0, 100)] },
+      { ...GAIA, stars: [at(2, 0.0005, 0, 100)] }
+    ]);
+    expect(stars).toHaveLength(1);
   });
 
   it('handles a single catalogue as a plain pass-through', () => {
@@ -146,3 +237,35 @@ describe('mergeStarCatalogues', () => {
     expect(Date.now() - started).toBeLessThan(10000);
   });
 });
+
+describe('placementDistancePc', () => {
+  it("draws a star both surveys measured at Gaia's distance", () => {
+    expect(placementDistancePc(120, 118.4, 250)).toBe(118.4);
+  });
+
+  // The case the old cut got wrong: Hipparcos inside, Gaia outside. Kept, at the distance Gaia
+  // gives, rather than at one a third short or dropped for having been misplaced.
+  it('keeps a star Hipparcos put inside the cutoff, where Gaia puts it, even past the cutoff', () => {
+    expect(placementDistancePc(200, 306, 250)).toBe(306);
+  });
+
+  // The mirror image: Hipparcos outside, Gaia inside. The Gaia download already holds the star,
+  // and keeping the HYG row is what lets the merge give that entry its name.
+  it('keeps a star only Gaia puts inside the cutoff', () => {
+    expect(placementDistancePc(262, 241, 250)).toBe(241);
+  });
+
+  it('keeps a star Gaia measured and Hipparcos gave no distance for', () => {
+    expect(placementDistancePc(undefined, 180, 250)).toBe(180);
+  });
+
+  it('falls back to Hipparcos where Gaia has no usable distance', () => {
+    expect(placementDistancePc(90, undefined, 250)).toBe(90);
+  });
+
+  it('drops a star both surveys put outside, or neither measured', () => {
+    expect(placementDistancePc(300, 410, 250)).toBeNull();
+    expect(placementDistancePc(300, undefined, 250)).toBeNull();
+    expect(placementDistancePc(undefined, undefined, 250)).toBeNull();
+  });
+});

src/app/shared/astro/star-merge.ts

@@ -1,3 +1,4 @@
+import { isDesignation } from '../models/star-catalog';
 import { StarRecord } from '../models/star.model';
 
 /**
@@ -17,8 +18,47 @@ import { StarRecord } from '../models/star.model';
 
 const DEG_TO_RAD = Math.PI / 180;
 
-/** Angular separation, in degrees, below which two entries are taken to be the same star. */
+/**
-export const MERGE_ANGULAR_TOLERANCE_DEG = 1 / 3600;
+ * Angular separation, in degrees, below which two entries are taken to be the same star.
+ *
+ * Every source arrives here at epoch J2000.0 — HYG publishes it, Gaia is carried back to it with
+ * its own proper motions in `gaia.ts` — so what separates two entries of one star is measurement,
+ * not motion. Left at their own epochs, sixteen years of proper motion put Proxima's two entries
+ * 62″ apart and Barnard's 166″, and an arcsecond of tolerance kept every fast star twice while
+ * folding the slow ones.
+ *
+ * What measurement leaves is under an arcsecond for a Hipparcos position — 55 457 of the 56 000
+ * stars both catalogues hold — and up to tens of arcseconds for the Gliese-only entries HYG
+ * carries without Hipparcos astrometry: Wolf 359 sits 5″ from where Gaia has it, Ross 248 12″.
+ * Fifteen arcseconds takes those. The sky is sparse enough at this depth that shifting every
+ * entry a quarter of a degree finds only 16 chance neighbours within it, against 116 real ones
+ * between ten and fifteen; past twenty the two curves run together.
+ */
+export const MERGE_ANGULAR_TOLERANCE_DEG = 15 / 3600;
+
+/**
+ * Angular separation, in degrees, under which the distances are not consulted. A coincidence of
+ * direction this close is never chance at this depth — the quarter-degree shift finds none under
+ * 3″ — so two entries this close are one star whatever their parallaxes say, and what they say
+ * is often a Hipparcos parallax off by half: 1 500 stars sat within this of their Gaia entry and
+ * were kept twice by the distance test, thirty of them at a false few parsecs from the Sun
+ * (HIP 82724 at 3.7 pc, where Gaia has it at 62.8). Brightness keeps its say at any separation,
+ * because a companion can sit this close: Ashlesha's is 2.7″ away and three magnitudes fainter.
+ */
+export const MERGE_CERTAIN_ANGULAR_TOLERANCE_DEG = 3 / 3600;
+
+/**
+ * How much fainter, and how much brighter, an entry may be than the one it is folded into and
+ * still be the same star. Bands differ, and not symmetrically: a red dwarf is three magnitudes
+ * fainter in HYG's V than in Gaia's G, so the folded entry may be up to five fainter. A star is
+ * never much brighter in V than in G, though, and an entry a magnitude brighter than what is
+ * already at that spot is a primary Gaia does not carry — it saturates below G ≈ 3 — sitting
+ * beside its companion: Sirius 6″ from Sirius B and ten magnitudes brighter, Almach 10″ from
+ * γ² And, Alfirk 13″ from β Cep B. Without this the primary's name lands on the companion's
+ * entry, and the companion is gone.
+ */
+export const MERGE_FAINTER_TOLERANCE = 5;
+export const MERGE_BRIGHTER_TOLERANCE = 1;
 
 /**
  * How far two distances may disagree, as a ratio, and still describe the same star. Generous on
@@ -27,6 +67,28 @@ export const MERGE_ANGULAR_TOLERANCE_DEG = 1 / 3600;
  */
 export const MERGE_DISTANCE_RATIO_TOLERANCE = 0.5;
 
+/**
+ * Where to draw a star Hipparcos and Gaia both measured, and whether the map keeps it at all.
+ *
+ * Gaia's distance wherever it has a usable one, since its parallaxes are fifty times more
+ * precise; Hipparcos's otherwise. The two catalogues used to be cut at the same radius, each on
+ * its own distance, so a star Hipparcos put at 200 pc and Gaia at 300 was kept by one, never
+ * downloaded from the other, and drawn at 200. That was 83% of the HYG stars left without a
+ * Gaia counterpart, and at the median Hipparcos had them at two-thirds of Gaia's distance.
+ *
+ * Now a star either survey places inside `cutoffPc` is kept, and every kept star sits where the
+ * better measurement puts it, inside the cutoff or not. `null` for a star neither survey places
+ * inside, or that no survey gives a distance for.
+ */
+export function placementDistancePc(hipparcosPc: number | undefined, gaiaPc: number | undefined, cutoffPc: number): number | null {
+  const best = gaiaPc ?? hipparcosPc;
+  if (best === undefined) {
+    return null;
+  }
+  const inside = best <= cutoffPc || (hipparcosPc !== undefined && hipparcosPc <= cutoffPc);
+  return inside ? best : null;
+}
+
 export interface MergeCandidate {
   readonly sourceId: string;
   /** Lower is better — the parallax precision this source measures with, in milliarcseconds. */
@@ -36,7 +98,7 @@ export interface MergeCandidate {
 
 export interface MergeSummary {
   readonly total: number;
-  /** Entries dropped because a better-measured catalogue already had that star. */
+  /** Entries folded into one a better-measured catalogue already had; see {@link combine}. */
   readonly duplicates: number;
   readonly bySource: Readonly<Record<string, number>>;
 }
@@ -60,8 +122,13 @@ function distanceOf(star: StarRecord): number {
  */
 const SKY_CELL_DEG = 0.5;
 
+const RA_CELLS = 360 / SKY_CELL_DEG;
+
 function cellKey(raDeg: number, decDeg: number): string {
-  return `${Math.floor(raDeg / SKY_CELL_DEG)}:${Math.floor(decDeg / SKY_CELL_DEG)}`;
+  // Right ascension wraps: the cell after 359.5° is 0°, so a pair straddling 0h shares a
+  // neighbourhood rather than sitting 719 cells apart.
+  const raCell = ((Math.floor(raDeg / SKY_CELL_DEG) % RA_CELLS) + RA_CELLS) % RA_CELLS;
+  return `${raCell}:${Math.floor(decDeg / SKY_CELL_DEG)}`;
 }
 
 function skyAngles(star: StarRecord): { raDeg: number; decDeg: number } {
@@ -86,9 +153,13 @@ export function directionCosine(a: StarRecord, b: StarRecord): number {
   return Math.max(-1, Math.min(1, ax * bx + ay * by + az * bz));
 }
 
-/** Whether two entries describe the same star: same direction, and distances not in conflict. */
+/**
-export function isSameStar(a: StarRecord, b: StarRecord): boolean {
+ * Whether `entry` describes the star already `kept`: the same direction, the brightness not in
-  const [near, far] = [distanceOf(a), distanceOf(b)].sort((p, q) => p - q);
+ * conflict and — unless the directions agree closely enough to settle it — the distance not in
+ * conflict either.
+ */
+export function isSameStar(kept: StarRecord, entry: StarRecord): boolean {
+  const [near, far] = [distanceOf(kept), distanceOf(entry)].sort((p, q) => p - q);
 
   // The Sun sits at the origin of this coordinate system and so has no direction at all, which
   // the angular test below cannot speak about. Every catalogue contains it, so without this the
@@ -97,25 +168,53 @@ export function isSameStar(a: StarRecord, b: StarRecord): boolean {
     return far === 0;
   }
 
-  const separationDeg = Math.acos(directionCosine(a, b)) / DEG_TO_RAD;
+  const separationDeg = Math.acos(directionCosine(kept, entry)) / DEG_TO_RAD;
   if (separationDeg > MERGE_ANGULAR_TOLERANCE_DEG) {
     return false;
   }
+  const fainterBy = entry.magnitude - kept.magnitude;
+  if (fainterBy < -MERGE_BRIGHTER_TOLERANCE || fainterBy > MERGE_FAINTER_TOLERANCE) {
+    return false;
+  }
+
+  if (separationDeg <= MERGE_CERTAIN_ANGULAR_TOLERANCE_DEG) {
+    return true;
+  }
 
   return (far - near) / near <= MERGE_DISTANCE_RATIO_TOLERANCE;
 }
 
+/**
+ * One entry from two of the same star: the position of the better-measured one — inserted first,
+ * so it is the one already `kept` — and the description of whichever knows the star as more than
+ * a catalogue number. HYG's "Proxima Centauri", "M5Ve" and V magnitude over Gaia's
+ * "Gaia DR3 5853498713190525696", "Unknown" and G; keeping either row whole loses half of that,
+ * and keeping Gaia's whole once cost the map 102 proper names and 32 000 spectral types. The id
+ * travels with the description, so a star HYG knows keeps its HYG id from one refresh to the next;
+ * `source` stays with the position, since that is what it records.
+ */
+function combine(kept: StarRecord, other: StarRecord): StarRecord {
+  const described = isDesignation(kept) && !isDesignation(other) ? other : kept;
+  return { ...described, x: kept.x, y: kept.y, z: kept.z, source: kept.source };
+}
+
 /**
  * Unions the given catalogues, keeping one entry per star.
  *
- * Sources are taken in order of how precisely they measure parallax, best first, and a star is
+ * Sources are taken in order of how precisely they measure parallax, best first. An entry that a
- * only added if no better-measured catalogue already has it. So where Gaia and Hipparcos
+ * better-measured catalogue already has is folded into that entry — the nearest one within the
- * overlap, the position is Gaia's; where only Hipparcos reaches, the star is still there.
+ * tolerance, see {@link combine} for what each side keeps. Only entries from *other* sources
+ * count as already there: a catalogue does not list a star twice, so two of its own entries
+ * within the tolerance are two stars, typically a double that Gaia resolves and Hipparcos did
+ * not. Where only one source reaches, the star is still there.
  */
 export function mergeStarCatalogues(candidates: readonly MergeCandidate[]): { stars: StarRecord[]; summary: MergeSummary } {
   const ordered = [...candidates].sort((a, b) => a.parallaxPrecisionMas - b.parallaxPrecisionMas);
   const merged: StarRecord[] = [];
-  const grid = new Map<string, StarRecord[]>();
+  const grid = new Map<string, number[]>();
+  // Entries that already absorbed one from a source, as `${index}/${source}`: a double that
+  // Gliese lists as two entries at one position has to land on two Gaia entries, not on one.
+  const taken = new Set<string>();
   const bySource: Record<string, number> = {};
   let duplicates = 0;
 
@@ -123,24 +222,41 @@ export function mergeStarCatalogues(candidates: readonly MergeCandidate[]): { st
     bySource[candidate.sourceId] = 0;
 
     for (const star of candidate.stars) {
-      const { raDeg, decDeg } = skyAngles(star);
+      const entry: StarRecord = { ...star, source: star.source ?? candidate.sourceId };
-      const alreadyPresent = neighbouringCells(raDeg, decDeg).some((key) => (grid.get(key) ?? []).some((existing) => isSameStar(existing, star)));
+      const { raDeg, decDeg } = skyAngles(entry);
 
-      if (alreadyPresent) {
+      let match: number | null = null;
+      let matchCosine = -1;
+      for (const key of neighbouringCells(raDeg, decDeg)) {
+        for (const index of grid.get(key) ?? []) {
+          const existing = merged[index];
+          if (existing.source === entry.source || taken.has(`${index}/${entry.source}`) || !isSameStar(existing, entry)) {
+            continue;
+          }
+          const cosine = directionCosine(existing, entry);
+          if (cosine > matchCosine) {
+            match = index;
+            matchCosine = cosine;
+          }
+        }
+      }
+
+      if (match !== null) {
+        merged[match] = combine(merged[match], entry);
+        taken.add(`${match}/${entry.source}`);
         duplicates++;
         continue;
       }
 
-      const withSource: StarRecord = { ...star, source: star.source ?? candidate.sourceId };
+      const index = merged.push(entry) - 1;
-      merged.push(withSource);
       bySource[candidate.sourceId]++;
 
       const key = cellKey(raDeg, decDeg);
       const cell = grid.get(key);
       if (cell) {
-        cell.push(withSource);
+        cell.push(index);
       } else {
-        grid.set(key, [withSource]);
+        grid.set(key, [index]);
       }
     }
   }

src/app/shared/astro/star-neighbourhood.spec.ts

@@ -115,4 +115,49 @@ describe('StarNeighbourhood', () => {
 
     expect(ids(index.nearest(1, 2)).sort()).toEqual([2, 3]);
   });
+
+  /** 400 stars scattered 20 pc either side of the origin on every axis, so cells on both sides of zero. */
+  function cloud(): StarPoint[] {
+    let seed = 3;
+    const random = () => ((seed = (seed * 1103515245 + 12345) % 2147483648) / 2147483648) * 40 - 20;
+    return Array.from({ length: 400 }, (_, id) => ({ id, x: random(), y: random(), z: random() }));
+  }
+
+  it('visits every star within a radius and no other', () => {
+    const points = cloud();
+    const origin = points[0];
+    const expected = points
+      .filter((point) => point.id !== origin.id && Math.hypot(point.x - origin.x, point.y - origin.y, point.z - origin.z) <= 7)
+      .map((point) => point.id)
+      .sort((a, b) => a - b);
+
+    const visited: number[] = [];
+    new StarNeighbourhood(points).forEachWithin(origin.id, 7, (neighbour) => visited.push(neighbour.id));
+
+    expect(visited.sort((a, b) => a - b)).toEqual(expected);
+  });
+
+  // The pair walk reads each cell's indices back out of its key; read wrong, it quietly drops
+  // pairs instead of failing.
+  it('walks every pair within a radius exactly once', () => {
+    const points = cloud();
+    let expected = 0;
+    for (let i = 0; i < points.length; i++) {
+      for (let j = i + 1; j < points.length; j++) {
+        if (Math.hypot(points[j].x - points[i].x, points[j].y - points[i].y, points[j].z - points[i].z) <= 5) {
+          expected++;
+        }
+      }
+    }
+
+    const walked = new Set<string>();
+    let visits = 0;
+    new StarNeighbourhood(points).forEachPairWithin(5, (a, b) => {
+      visits++;
+      walked.add(a.id < b.id ? `${a.id}-${b.id}` : `${b.id}-${a.id}`);
+    });
+
+    expect(visits).toBe(expected);
+    expect(walked.size).toBe(expected);
+  });
 });

src/app/shared/astro/star-neighbourhood.ts

@@ -38,12 +38,27 @@ const DEFAULT_CELL_SIZE_PC = 5;
 /** Grows the search a shell of cells at a time; the cap stops a query in empty space forever. */
 const MAX_RING = 12;
 
-function cellKey(ix: number, iy: number, iz: number): string {
+/**
-  return `${ix},${iy},${iz}`;
+ * Cells are keyed by one number packed from their three indices rather than by a string. A route
+ * search visits up to 125 cells for every star it expands, and building `"ix,iy,iz"` for each
+ * was half of what a route cost. Room for 65 536 cells either side of the Sun on every axis,
+ * 330 kpc at the default cell size, and the packed key stays inside a double's exact integers.
+ */
+const CELL_OFFSET = 65_536;
+const CELL_SPAN = 131_072;
+
+function cellKey(ix: number, iy: number, iz: number): number {
+  return ((ix + CELL_OFFSET) * CELL_SPAN + (iy + CELL_OFFSET)) * CELL_SPAN + (iz + CELL_OFFSET);
+}
+
+function cellIndices(key: number): [number, number, number] {
+  const iz = (key % CELL_SPAN) - CELL_OFFSET;
+  const rest = Math.floor(key / CELL_SPAN);
+  return [Math.floor(rest / CELL_SPAN) - CELL_OFFSET, (rest % CELL_SPAN) - CELL_OFFSET, iz];
 }
 
 export class StarNeighbourhood {
-  private readonly cells = new Map<string, number[]>();
+  private readonly cells = new Map<number, number[]>();
   private readonly points: readonly StarPoint[];
   private readonly indexById = new Map<number, number>();
   private readonly cellSizePc: number;
@@ -64,6 +79,16 @@ export class StarNeighbourhood {
     });
   }
 
+  /** Where the star this id names sits in the list the index was built from, or `undefined`. */
+  indexOf(id: number): number | undefined {
+    return this.indexById.get(id);
+  }
+
+  /** The star at this position in the list the index was built from. */
+  pointAt(index: number): StarPoint {
+    return this.points[index];
+  }
+
   /** The star this id names, or `undefined` — the caller's id may not be in the catalogue. */
   point(id: number): StarPoint | undefined {
     const index = this.indexById.get(id);
@@ -135,34 +160,52 @@ export class StarNeighbourhood {
    * a jump-link graph is built from: one call per node gives that node's edges.
    */
   within(id: number, radiusPc: number): Neighbour[] {
-    const origin = this.point(id);
+    const found: Neighbour[] = [];
-    if (!origin || radiusPc <= 0) {
+    this.forEachWithin(id, radiusPc, (neighbour, distancePc) => found.push({ id: neighbour.id, distancePc }));
-      return [];
+    found.sort((a, b) => a.distancePc - b.distancePc);
+    return found;
   }
 
-    const found: Neighbour[] = [];
+  /**
+   * The same stars as `within`, handed over one at a time in no particular order. What a search
+   * that expands thousands of stars wants: it has no use for each star's neighbours sorted and
+   * collected into a list, which was the other half of what a route cost.
+   *
+   * A distance is compared as a distance, not as its square, here and in the pair walk: squaring
+   * a range can round it just under the square of the very hop it was read from, and then a
+   * range set to a reported distance would not admit that hop again.
+   */
+  forEachWithin(id: number, radiusPc: number, visit: (neighbour: StarPoint, distancePc: number) => void): void {
+    const origin = this.point(id);
+    if (!origin || radiusPc <= 0) {
+      return;
+    }
     const [ox, oy, oz] = this.cellFor(origin.x, origin.y, origin.z);
     const reach = Math.ceil(radiusPc / this.cellSizePc);
 
     for (let ix = ox - reach; ix <= ox + reach; ix++) {
       for (let iy = oy - reach; iy <= oy + reach; iy++) {
         for (let iz = oz - reach; iz <= oz + reach; iz++) {
-          for (const index of this.cells.get(cellKey(ix, iy, iz)) ?? []) {
+          const cell = this.cells.get(cellKey(ix, iy, iz));
+          if (!cell) {
+            continue;
+          }
+          for (const index of cell) {
             const candidate = this.points[index];
             if (candidate.id === id) {
               continue;
             }
-            const distancePc = Math.hypot(candidate.x - origin.x, candidate.y - origin.y, candidate.z - origin.z);
+            const dx = candidate.x - origin.x;
+            const dy = candidate.y - origin.y;
+            const dz = candidate.z - origin.z;
+            const distancePc = Math.sqrt(dx * dx + dy * dy + dz * dz);
             if (distancePc <= radiusPc) {
-              found.push({ id: candidate.id, distancePc });
+              visit(candidate, distancePc);
             }
           }
         }
       }
     }
-
-    found.sort((a, b) => a.distancePc - b.distancePc);
-    return found;
   }
 
   /**
@@ -181,10 +224,9 @@ export class StarNeighbourhood {
       return;
     }
     const reach = Math.ceil(radiusPc / this.cellSizePc);
-    const radiusSq = radiusPc * radiusPc;
 
     for (const [key, cell] of this.cells) {
-      const [ix, iy, iz] = key.split(',').map(Number);
+      const [ix, iy, iz] = cellIndices(key);
       for (let dx = 0; dx <= reach; dx++) {
         for (let dy = dx === 0 ? 0 : -reach; dy <= reach; dy++) {
           for (let dz = dx === 0 && dy === 0 ? 0 : -reach; dz <= reach; dz++) {
@@ -202,9 +244,9 @@ export class StarNeighbourhood {
                 const dxp = b.x - a.x;
                 const dyp = b.y - a.y;
                 const dzp = b.z - a.z;
-                const distanceSq = dxp * dxp + dyp * dyp + dzp * dzp;
+                const distancePc = Math.sqrt(dxp * dxp + dyp * dyp + dzp * dzp);
-                if (distanceSq <= radiusSq) {
+                if (distancePc <= radiusPc) {
-                  visit(a, b, Math.sqrt(distanceSq));
+                  visit(a, b, distancePc);
                 }
               }
             }
@@ -214,7 +256,7 @@ export class StarNeighbourhood {
     }
   }
 
-  private keyFor(x: number, y: number, z: number): string {
+  private keyFor(x: number, y: number, z: number): number {
     const [ix, iy, iz] = this.cellFor(x, y, z);
     return cellKey(ix, iy, iz);
   }

src/app/shared/format/scale-bar.spec.ts

@@ -0,0 +1,100 @@
+import { describe, expect, it } from 'vitest';
+
+import { distanceRings, formatRoundLength, roundLengthAtMost, scaleBar } from './scale-bar';
+
+describe('roundLengthAtMost', () => {
+  it('rounds down to 1, 2 or 5 times a power of ten', () => {
+    expect(roundLengthAtMost(51)).toBe(50);
+    expect(roundLengthAtMost(3.3)).toBe(2);
+    expect(roundLengthAtMost(0.7)).toBe(0.5);
+    expect(roundLengthAtMost(1999)).toBe(1000);
+  });
+
+  it('keeps a length that is already round, including at a decade', () => {
+    expect(roundLengthAtMost(1000)).toBe(1000);
+    expect(roundLengthAtMost(100)).toBe(100);
+    expect(roundLengthAtMost(5)).toBe(5);
+    expect(roundLengthAtMost(0.2)).toBe(0.2);
+  });
+
+  it('has no length for nothing', () => {
+    for (const value of [0, -1, Number.NaN, Number.POSITIVE_INFINITY]) {
+      expect(roundLengthAtMost(value)).toBeNull();
+    }
+  });
+});
+
+describe('distanceRings', () => {
+  // The opening view sits about 307 pc from the Sun: the rings the map always had, with the
+  // survey edge at the fifth, and on out past the camera for the stars now drawn beyond it.
+  it('reaches past the camera from the opening view', () => {
+    expect(distanceRings(0, 307, 5, 250)).toEqual([50, 100, 150, 200, 250, 300, 350]);
+  });
+
+  it('closes in with the camera', () => {
+    expect(distanceRings(0, 20, 5, 250)).toEqual([2, 4, 6, 8, 10, 12, 14, 16, 18, 20]);
+    expect(distanceRings(0, 1, 5, 250)).toEqual([0.2, 0.4, 0.6, 0.8, 1]);
+  });
+
+  // Near Mirfak the camera is 155 pc out; rounding the step down to 20 pc must not leave the
+  // rings stopping at 100.
+  it('covers the whole distance whatever the rounding', () => {
+    expect(distanceRings(0, 155, 5, 250)).toEqual([20, 40, 60, 80, 100, 120, 140, 160]);
+  });
+
+  // A star 190 pc out seen from 20 pc away: the frame is a band about 19 pc either side of it and
+  // the Sun is nowhere in it. Sized to the 210 pc it reaches, the step would be 20 pc and the
+  // nearest rings — 180 and 200 — would both miss the frame.
+  it('spaces the rings for a frame that does not hold the Sun', () => {
+    const radii = distanceRings(171, 210, 5, 250);
+
+    expect(radii).toEqual([170, 175, 180, 185, 190, 195, 200, 205, 210]);
+    expect(radii.some((radius) => Math.abs(radius - 190) < 19)).toBe(true);
+  });
+
+  it('marks the callout among rings the step does not land on', () => {
+    expect(distanceRings(0, 1000, 5, 250)).toEqual([200, 250, 400, 600, 800, 1000]);
+  });
+
+  it('leaves the callout out when it is past the last ring, or behind the first', () => {
+    expect(distanceRings(0, 100, 5, 250)).toEqual([20, 40, 60, 80, 100]);
+    // Short of the survey edge by less than one step is not the rule — the last ring is: 245 pc
+    // overshoots to 260 and gets it, 235 pc stops at 240 and does not, on the same 20 pc step.
+    expect(distanceRings(0, 245, 5, 250)).toContain(250);
+    expect(distanceRings(0, 235, 5, 250)).not.toContain(250);
+    expect(distanceRings(400, 440, 5, 250)).toEqual([400, 405, 410, 415, 420, 425, 430, 435, 440]);
+  });
+
+  it('draws no rings for a camera with no distance', () => {
+    expect(distanceRings(0, 0, 5, 250)).toEqual([]);
+  });
+});
+
+describe('scaleBar', () => {
+  it('picks the longest round length that fits, and the width it spans', () => {
+    // A tenth of a parsec a pixel and 120 px of room: 12 pc would fit, and the round length
+    // under it is 10 pc, which spans 100 px.
+    expect(scaleBar(0.1, 120, 'pc')).toEqual({ label: '10 pc', widthPx: 100 });
+  });
+
+  it('draws nothing for a view with no extent', () => {
+    expect(scaleBar(0, 120, 'pc')).toBeNull();
+  });
+});
+
+describe('formatRoundLength', () => {
+  it('reads without trailing zeros, in kiloparsecs past a thousand', () => {
+    expect(formatRoundLength(2000, 'pc')).toBe('2 kpc');
+    expect(formatRoundLength(500, 'pc')).toBe('500 pc');
+    expect(formatRoundLength(0.2, 'pc')).toBe('0.2 pc');
+    expect(formatRoundLength(0.05, 'AU')).toBe('0.05 AU');
+  });
+
+  // Ring radii are multiples of a round step rather than round themselves; a one-digit format
+  // printed the 250 pc survey edge as "300 pc".
+  it('keeps every digit of a ring radius', () => {
+    expect(formatRoundLength(250, 'pc')).toBe('250 pc');
+    expect(formatRoundLength(150, 'pc')).toBe('150 pc');
+    expect(formatRoundLength(2500, 'pc')).toBe('2.5 kpc');
+  });
+});

src/app/shared/format/scale-bar.ts

@@ -0,0 +1,86 @@
+/**
+ * The round lengths a map is read against: its scale bar, and the spacing of its distance rings.
+ *
+ * Round means 1, 2 or 5 times a power of ten — the only lengths a reader can add up at a glance,
+ * which is why every printed map's scale bar uses them.
+ */
+
+/** The largest 1, 2 or 5 × a power of ten that is at most `value`, or `null` for no length at all. */
+export function roundLengthAtMost(value: number): number | null {
+  if (!Number.isFinite(value) || value <= 0) {
+    return null;
+  }
+  const power = 10 ** Math.floor(Math.log10(value));
+  const mantissa = value / power;
+  return (mantissa >= 5 ? 5 : mantissa >= 2 ? 2 : 1) * power;
+}
+
+/**
+ * Rings across the span from `nearest` to `reach`, at a round step of about a `count`th of it,
+ * plus `callout` where it falls between the first ring and the last: the grid's own radii are
+ * round, and the one radius that means something in its own right is marked whether the step lands
+ * on it or not. A frame that stops short of it gets it only when the last ring — the first multiple
+ * of `step` at or past `reach` — is past it: reach 245 with a 20 pc step gets it, reach 235 does
+ * not, since its last ring is 240.
+ *
+ * Two numbers rather than one because these rings are centred on a fixed point — the Sun — and a
+ * frame need not be. Looking at something 200 pc out from 20 pc away, what is on screen is a band
+ * 200 pc wide at its narrowest and nowhere near the Sun; a step sized to the whole 220 puts every
+ * ring off the frame. The span is what the frame covers, so the step is what it can resolve.
+ *
+ * Rounding the step down, over a span that need not start at the Sun, makes for `count` to
+ * `ceil(2.5 × count) + 2` rings — `ceil(reach / step) - floor(nearest / step) + 1` — and the
+ * callout can add one: 5 to 16 for a count of 5.
+ */
+export function distanceRings(nearest: number, reach: number, count: number, callout: number): number[] {
+  const step = roundLengthAtMost((reach - nearest) / count);
+  if (step === null) {
+    return [];
+  }
+  // The ring just inside the near edge of the span, so the band is crossed rather than started at.
+  const first = Math.max(1, Math.floor(nearest / step));
+  const last = Math.ceil(reach / step);
+  // `toPrecision` clears the binary noise of stepping by a tenth: 0.1 × 3 is 0.30000000000000004.
+  const radii = Array.from({ length: last - first + 1 }, (_, index) => Number((step * (first + index)).toPrecision(12)));
+  if (callout > radii[0] && callout < radii[radii.length - 1] && !radii.includes(callout)) {
+    radii.push(callout);
+    radii.sort((a, b) => a - b);
+  }
+  return radii;
+}
+
+export type LengthUnit = 'pc' | 'AU';
+
+/** A round length, and how many pixels it spans at the current zoom. */
+export interface ScaleBar {
+  readonly label: string;
+  readonly widthPx: number;
+}
+
+/**
+ * The longest round length that fits in `maxWidthPx` when one pixel spans `unitsPerPx`.
+ *
+ * Under a perspective camera a pixel spans a different length at every depth, so the scene
+ * measures `unitsPerPx` at the point the view is centred on, which is where the map is being
+ * read. Under the plan view it is exact everywhere.
+ */
+export function scaleBar(unitsPerPx: number, maxWidthPx: number, unit: LengthUnit): ScaleBar | null {
+  const length = roundLengthAtMost(unitsPerPx * maxWidthPx);
+  if (length === null) {
+    return null;
+  }
+  return { label: formatRoundLength(length, unit), widthPx: length / unitsPerPx };
+}
+
+/** A scale or ring length, in kiloparsecs past a thousand parsecs. */
+export function formatRoundLength(length: number, unit: LengthUnit): string {
+  if (unit === 'pc' && length >= 1000) {
+    return `${digitsOf(length / 1000)} kpc`;
+  }
+  return `${digitsOf(length)} ${unit}`;
+}
+
+/** `0.05`, `2`, `150`, never `2.00`: these lengths have no digits past the ones that carry them. */
+function digitsOf(value: number): string {
+  return String(Number(value.toPrecision(3)));
+}

src/app/shared/models/body.model.ts

@@ -29,4 +29,14 @@ export interface BodyRecord {
    * relative to that planet, not heliocentrically. Undefined for planets/dwarfs.
    */
   parentBodyId?: string;
+  /**
+   * How the body turns on its own axis: the sidereal rotation period in hours, negative where
+   * Horizons gives a negative rate (Venus, Uranus), and the tilt of that axis from its orbital
+   * plane — which past 90 degrees already says the turn is retrograde.
+   *
+   * Absent where Horizons publishes neither — the view then leaves the body still rather than
+   * spinning it at an invented rate.
+   */
+  rotationPeriodHours?: number;
+  obliquityDeg?: number;
 }

src/app/shared/models/exoplanet.model.ts

@@ -21,17 +21,19 @@ export interface ExoplanetRecord {
   /** Host star mass in solar masses (`st_mass`); the fallback when no period is published. */
   hostStarMassSolar?: number;
   /**
-   * The host star's own published position (`ra`, `dec`, `sy_dist`) — the coordinates the
+   * The host star's own published astrometry (`ra`, `dec`, `sy_dist`, `sy_pmra`, `sy_pmdec`) —
-   * cross-reference above is resolved from.
+   * everything the cross-reference above was resolved from.
    *
    * Kept rather than consumed and discarded. `hostStarId` is the *result* of a match against
-   * whatever star catalogue was loaded at the time, so widening that catalogue ought to rescue
+   * whatever star catalogue was loaded at the time; keeping the inputs makes auditing or
-   * some of the 4347 hosts that currently resolve to nothing — but with only the result stored,
+   * redoing that match a local operation instead of a TAP query against an archive that is not
-   * redoing the match meant re-downloading the archive. These three numbers make it a local
+   * always reachable — it is how the matcher's tolerances were measured. See
-   * operation. See `rematchHostStars`.
+   * `resolveHostStarId`.
    */
   hostRaDeg?: number;
   hostDecDeg?: number;
   hostDistancePc?: number;
+  hostPmRaMasPerYear?: number;
+  hostPmDecMasPerYear?: number;
   orbit: Partial<OrbitalElements>;
 }

src/app/shared/rendering/texture-catalog.ts

@@ -4,18 +4,21 @@ import * as THREE from 'three/webgpu';
  * Real NASA/ESA/USGS photography baked into `src/assets/textures/bodies/` at build time,
  * keyed by the same ids used in `bodies.json`.
  *
- * This map is the whole of what has actually been photographed. Everything else — every
+ * Only surface *maps* belong here: equirectangular images, twice as wide as tall, that wrap a
- * exoplanet, since not one has ever been imaged, and the moons no probe returned a usable map
+ * sphere. Everything else — every exoplanet, since not one has ever been imaged, and every moon
- * of — falls through to `procedural-planet-texture.ts`, which derives a surface from the body's
+ * or dwarf planet with no such map in the repository — falls through to
- * own measured size, mass, orbit and host star instead.
+ * `procedural-planet-texture.ts`, which derives a surface from the body's own measured size,
+ * mass, orbit and host star instead.
  *
- * Provenance (all public domain NASA/JPL or CC BY 4.0 Solar System Scope, via Wikimedia
+ * Io, Pluto, Titan and Deimos used to be listed with the square photographs of them in
- * Commons — see each file's Commons page for the original credit line):
+ * `assets/textures/bodies/`: pictures of a lit disc against black sky, not maps. Wrapped round a
- * mercury/venus/earth/mars/saturn/uranus/neptune/moon/sun/saturn-ring/skybox — Solar System
+ * sphere they put black sky on a fifth to a third of the surface, in a band up to 57 degrees wide
- * Scope texture pack (CC BY 4.0); jupiter — Solar System Scope 8k pack (CC BY 4.0); pluto —
+ * across the equator that the spin then swept past the camera. They are left out until a real map
- * NASA/JHUAPL/SwRI New Horizons true-color mosaic; deimos — NASA/JPL/University of Arizona
+ * of each is added.
- * MRO HiRISE; io — NASA/JPL Galileo highest-resolution true-color mosaic; titan — NASA/JPL
+ *
- * Cassini true-color view.
+ * Provenance (CC BY 4.0 Solar System Scope, via Wikimedia Commons — see each file's Commons page
+ * for the original credit line): mercury/venus/earth/mars/saturn/uranus/neptune/moon/sun/
+ * saturn-ring/skybox — Solar System Scope texture pack; jupiter — Solar System Scope 8k pack.
  */
 const BODY_TEXTURE_PATHS: Record<string, string> = {
   mercury: 'assets/textures/bodies/mercury.jpg',
@@ -26,11 +29,7 @@ const BODY_TEXTURE_PATHS: Record<string, string> = {
   saturn: 'assets/textures/bodies/saturn.jpg',
   uranus: 'assets/textures/bodies/uranus.jpg',
   neptune: 'assets/textures/bodies/neptune.jpg',
-  pluto: 'assets/textures/bodies/pluto.jpg',
+  moon: 'assets/textures/bodies/moon.jpg'
-  moon: 'assets/textures/bodies/moon.jpg',
-  deimos: 'assets/textures/bodies/deimos.jpg',
-  io: 'assets/textures/bodies/io.jpg',
-  titan: 'assets/textures/bodies/titan.jpg'
 };
 
 /** The Sun isn't a `BodyRecord` (it's the system's star marker), so it's looked up separately. */

src/app/shared/state/time.store.spec.ts

@@ -0,0 +1,74 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { TimeStore } from './time.store';
+
+const MS_PER_DAY = 86_400_000;
+const START = new Date('2026-09-22T12:00:00Z');
+
+describe('TimeStore', () => {
+  let time: TimeStore;
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(START);
+    time = new TimeStore();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('keeps the world’s own time until asked otherwise', () => {
+    const opened = time.julianDate();
+    vi.advanceTimersByTime(10_000);
+
+    expect(time.julianDate() - opened).toBeCloseTo(10_000 / MS_PER_DAY, 9);
+    expect(time.date().toISOString()).toBe('2026-09-22T12:00:10.000Z');
+  });
+
+  it('runs the sky faster without moving where it starts from', () => {
+    const opened = time.julianDate();
+    time.setRate(3600);
+    vi.advanceTimersByTime(1000);
+
+    // A second of watching is an hour of sky, and the date did not jump when the rate changed.
+    expect(time.julianDate() - opened).toBeCloseTo(1 / 24, 9);
+  });
+
+  it('carries on from where it had got to when the rate changes again', () => {
+    time.setRate(86_400);
+    vi.advanceTimersByTime(2000); // two days of sky
+    const afterTwoDays = time.julianDate();
+
+    time.setRate(1);
+    vi.advanceTimersByTime(1000);
+
+    // Slowing down keeps the two days: it does not rewind to the wall clock.
+    expect(time.julianDate() - afterTwoDays).toBeCloseTo(1000 / MS_PER_DAY, 9);
+    expect(time.julianDate() - afterTwoDays).toBeLessThan(1 / 24);
+  });
+
+  it('knows the map is away from now even once it is back at real time', () => {
+    expect(time.atNow()).toBe(true);
+    time.setRate(2_629_800);
+    vi.advanceTimersByTime(5000);
+    time.setRate(1);
+
+    // Real time, months ahead: the rate says nothing about where the clock stands.
+    expect(time.atNow()).toBe(false);
+    time.reset();
+    expect(time.atNow()).toBe(true);
+  });
+
+  it('comes back to now, at real time', () => {
+    time.setRate(2_629_800);
+    vi.advanceTimersByTime(5000); // months away
+    expect(time.date().getUTCFullYear()).toBeGreaterThan(START.getUTCFullYear());
+
+    time.reset();
+
+    expect(time.rate()).toBe(1);
+    // Now, not the moment the store was built: five seconds of wall clock have passed.
+    expect(time.date().toISOString()).toBe(new Date(START.getTime() + 5000).toISOString());
+  });
+});

src/app/shared/state/time.store.ts

@@ -0,0 +1,82 @@
+import { Injectable, signal } from '@angular/core';
+
+import { dateToJulianDate } from '../astro/constants';
+
+/**
+ * How fast the map's clock runs, in seconds of sky per second of wall clock.
+ *
+ * The map is built on propagated orbits and published rotation periods, both of which are
+ * functions of a date — so the only thing standing between it and a working orrery is the number
+ * on this list. At real time nothing appears to move: Earth turns 15 degrees an hour and takes a
+ * year to go round, and a reader watching for a minute sees a still picture.
+ *
+ * An hour a second is the rate at which rotation reads — Jupiter turns once every ten seconds of
+ * watching. A day a second is the rate at which the inner planets read. A month a second carries
+ * the outer ones, at which point the inner four are a blur, which is honest: that is what the
+ * solar system does.
+ */
+export const TIME_RATES = [
+  { label: 'Real time', secondsPerSecond: 1 },
+  { label: '1 h/s', secondsPerSecond: 3600 },
+  { label: '1 d/s', secondsPerSecond: 86_400 },
+  { label: '1 mo/s', secondsPerSecond: 2_629_800 },
+] as const;
+
+const MS_PER_DAY = 86_400_000;
+const JULIAN_DATE_AT_EPOCH = 2440587.5;
+
+/**
+ * The date the map is drawn for.
+ *
+ * Read every frame rather than held in a signal: it changes continuously, and a signal that
+ * changed sixty times a second would ask the whole HUD to re-render for a number nothing is
+ * watching. The rate *is* a signal, since a reader sets it and the controls read it back.
+ *
+ * Changing the rate re-anchors instead of rewinding: the date carries on from where it had got
+ * to, so speeding up and slowing down never jumps the sky.
+ */
+@Injectable({ providedIn: 'root' })
+export class TimeStore {
+  readonly rate = signal<number>(TIME_RATES[0].secondsPerSecond);
+  /**
+   * Whether the map is drawn for the present. Not the same as a rate of one: after an excursion at
+   * a month a second, real time carries on from months ahead, and the map is still away from now.
+   */
+  readonly atNow = signal(true);
+
+  private anchorJd = dateToJulianDate();
+  private anchorWallMs = Date.now();
+
+  /** Julian date for this instant, at the rate the reader chose. */
+  julianDate(): number {
+    return this.anchorJd + ((Date.now() - this.anchorWallMs) * this.rate()) / MS_PER_DAY;
+  }
+
+  /**
+   * The same instant as a date, for anything that prints it.
+   *
+   * Rounded to the millisecond, which is all a `Date` holds: a Julian date near 2 461 000 has
+   * about a twentieth of a millisecond of resolution left in a double, and `new Date` truncates
+   * what is left rather than rounding it, so ten seconds came back as 9.999.
+   */
+  date(): Date {
+    return new Date(Math.round((this.julianDate() - JULIAN_DATE_AT_EPOCH) * MS_PER_DAY));
+  }
+
+  setRate(secondsPerSecond: number): void {
+    this.anchorJd = this.julianDate();
+    this.anchorWallMs = Date.now();
+    this.rate.set(secondsPerSecond);
+    if (secondsPerSecond !== 1) {
+      this.atNow.set(false);
+    }
+  }
+
+  /** Back to now, at real time — the state the map opens in. */
+  reset(): void {
+    this.anchorJd = dateToJulianDate();
+    this.anchorWallMs = Date.now();
+    this.rate.set(TIME_RATES[0].secondsPerSecond);
+    this.atNow.set(true);
+  }
+}

src/assets/data/bodies.json

@@ -13,7 +13,9 @@
       "argumentOfPeriapsisDeg": 29.19561108948743,
       "meanAnomalyAtEpochDeg": 103.9465145977117,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": 1407.512239412851,
+    "obliquityDeg": 2.11
   },
   {
     "id": "venus",
@@ -29,7 +31,9 @@
       "argumentOfPeriapsisDeg": 55.15075425343929,
       "meanAnomalyAtEpochDeg": 280.0749102629981,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": -5832.539941165383,
+    "obliquityDeg": 177.3
   },
   {
     "id": "earth",
@@ -45,7 +49,9 @@
       "argumentOfPeriapsisDeg": 272.9783142442708,
       "meanAnomalyAtEpochDeg": 357.4122246804211,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": 23.934472399219285,
+    "obliquityDeg": 23.4392911
   },
   {
     "id": "mars",
@@ -61,7 +67,9 @@
       "argumentOfPeriapsisDeg": 286.7114828288203,
       "meanAnomalyAtEpochDeg": 124.444888195349,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": 24.622955438662025,
+    "obliquityDeg": 25.19
   },
   {
     "id": "jupiter",
@@ -77,7 +85,9 @@
       "argumentOfPeriapsisDeg": 273.6090683600047,
       "meanAnomalyAtEpochDeg": 58.98282567286461,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": 9.925102371306965,
+    "obliquityDeg": 3.13
   },
   {
     "id": "saturn",
@@ -93,7 +103,9 @@
       "argumentOfPeriapsisDeg": 337.1663598259115,
       "meanAnomalyAtEpochDeg": 264.9877650588944,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": 10.656221583138441,
+    "obliquityDeg": 26.73
   },
   {
     "id": "uranus",
@@ -109,7 +121,9 @@
       "argumentOfPeriapsisDeg": 90.49593456147204,
       "meanAnomalyAtEpochDeg": 255.8822481742851,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": -17.24003330792427,
+    "obliquityDeg": 97.77
   },
   {
     "id": "neptune",
@@ -125,7 +139,9 @@
       "argumentOfPeriapsisDeg": 268.1146665565159,
       "meanAnomalyAtEpochDeg": 319.6858384317641,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": 16.110037586020876,
+    "obliquityDeg": 28.32
   },
   {
     "id": "pluto",
@@ -141,7 +157,9 @@
       "argumentOfPeriapsisDeg": 113.5754868232679,
       "meanAnomalyAtEpochDeg": 51.93655343727463,
       "epochJd": 2460676.5
-    }
+    },
+    "rotationPeriodHours": 153.29335198,
+    "obliquityDeg": 119.6
   },
   {
     "id": "moon",
@@ -158,7 +176,9 @@
       "meanAnomalyAtEpochDeg": 290.7825171697369,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "earth"
+    "parentBodyId": "earth",
+    "rotationPeriodHours": 664.8546956215548,
+    "obliquityDeg": 6.67
   },
   {
     "id": "phobos",
@@ -175,7 +195,8 @@
       "meanAnomalyAtEpochDeg": 342.6005509941174,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "mars"
+    "parentBodyId": "mars",
+    "rotationPeriodHours": 7.660212212136228
   },
   {
     "id": "deimos",
@@ -192,7 +213,8 @@
       "meanAnomalyAtEpochDeg": 273.8943716897566,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "mars"
+    "parentBodyId": "mars",
+    "rotationPeriodHours": 30.304279685850094
   },
   {
     "id": "io",
@@ -209,7 +231,8 @@
       "meanAnomalyAtEpochDeg": 74.88524962049125,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "jupiter"
+    "parentBodyId": "jupiter",
+    "rotationPeriodHours": 42.51537583211252
   },
   {
     "id": "europa",
@@ -226,7 +249,8 @@
       "meanAnomalyAtEpochDeg": 40.72575250295771,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "jupiter"
+    "parentBodyId": "jupiter",
+    "rotationPeriodHours": 85.27848729079142
   },
   {
     "id": "ganymede",
@@ -243,7 +267,8 @@
       "meanAnomalyAtEpochDeg": 355.7249344187845,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "jupiter"
+    "parentBodyId": "jupiter",
+    "rotationPeriodHours": 171.78271980469088
   },
   {
     "id": "callisto",
@@ -260,7 +285,8 @@
       "meanAnomalyAtEpochDeg": 126.0198540648681,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "jupiter"
+    "parentBodyId": "jupiter",
+    "rotationPeriodHours": 400.52470451330635
   },
   {
     "id": "titan",
@@ -277,7 +303,8 @@
       "meanAnomalyAtEpochDeg": 32.18862839469676,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "saturn"
+    "parentBodyId": "saturn",
+    "rotationPeriodHours": 382.87527117206236
   },
   {
     "id": "triton",
@@ -294,6 +321,7 @@
       "meanAnomalyAtEpochDeg": 273.1157438944629,
       "epochJd": 2460676.5
     },
-    "parentBodyId": "neptune"
+    "parentBodyId": "neptune",
+    "rotationPeriodHours": 141.05626027628523
   }
 ]

tools/etl/build.ts

@@ -10,7 +10,6 @@ import { fetchSolarSystem } from './fetchSolarSystem';
 import { BYTES_PER_STAR_META, BYTES_PER_STAR_POSITION, decodeStarCatalog, encodeStarCatalog } from '../../src/app/shared/models/star-catalog';
 import { fetchStars } from './fetchStars';
 import { describeSources } from './sources/registry';
-import { rematchHostStars } from '../../src/app/shared/astro/host-star-matching';
 import { dataPath } from './lib/paths';
 
 class ValidationError extends Error {}
@@ -50,6 +49,87 @@ function validateStars(stars: StarRecord[]): void {
   }
 }
 
+/**
+ * What a good merge looks like, in two numbers the unit suite cannot see.
+ *
+ * The catalogues are regenerated by a scheduled job that pushes straight to `main` once the unit
+ * tests and a production build pass — and both passed, for weeks, on a catalogue carrying 23 000
+ * stars twice: the suite tests code against fixtures, and no fixture is 400 000 real stars. The
+ * two ways the merge has actually failed both show up here.
+ *
+ * A star kept twice leaves its two entries near each other on the sky, from *different* sources —
+ * one catalogue does not list a star twice. Under an arcsecond that is never two stars at this
+ * depth, so every such pair is a miss. Nineteen survive today, all of them a second HYG row
+ * wanting a Gaia entry that already absorbed one (Gliese lists some doubles twice); the merge
+ * that trusted a Hipparcos parallax over direction left 1 112.
+ *
+ * The other failure leaves no close pair at all, because proper motion had already carried the
+ * two entries tens of arcseconds apart — the 2026-08-24 refresh, where HYG sat at epoch 2000.0
+ * and Gaia at J2016.0. What it does leave is HYG rows that found no counterpart: 36 056 of them
+ * against the 10 886 today, and no counterpart was possible for most of those. Two thirds of them,
+ * 6 835, are the stars Gaia measures but the main query never downloads, because Gaia's parallax
+ * puts them past `ETL_GAIA_DISTANCE_PC` while Hipparcos put them inside `ETL_STAR_DISTANCE_PC`;
+ * they are every star in the published catalogue beyond 250 pc. The rest are what Gaia genuinely
+ * lacks: bright stars it saturates on, red dwarfs past its magnitude cut. So the headroom left to
+ * the ceiling tracks the gap between those two cutoffs as much as Gaia's completeness.
+ *
+ * This bounds a merge that went wrong, and — loosely — a Gaia download that came back short: a
+ * truncated answer leaves the HYG rows whose counterpart it dropped without one, so survivors go
+ * *up*, not down. Measured against the published catalogue: 10 886 today, 11 004 at nine tenths of
+ * the rows, 12 711 at half, 16 258 at a third. So this ceiling only catches a truncation past about
+ * two thirds, and `fetchGaiaStars` catches the shallower ones with its own row floor.
+ */
+const MAX_UNMERGED_TWINS = 100;
+const MAX_HYG_SURVIVORS = 15_000;
+const TWIN_TOLERANCE_RAD = (1 / 3600) * (Math.PI / 180);
+
+function validateMerge(stars: StarRecord[]): void {
+  // Checked first and on its own: an unreachable Gaia is skipped rather than thrown, and would
+  // otherwise surface below as "68 000 HYG stars found no counterpart" — true, and no help.
+  assertCondition(
+    stars.some((star) => star.source === 'gaia'),
+    'Gaia DR3 contributed no stars — the archive was unreachable or returned nothing, and a catalogue without it is not one to publish.'
+  );
+  const survivors = stars.filter((star) => star.source === 'hyg').length;
+  assertCondition(
+    survivors <= MAX_HYG_SURVIVORS,
+    `${survivors} HYG stars found no Gaia counterpart (at most ${MAX_HYG_SURVIVORS} expected) — the two catalogues are not being matched.`
+  );
+
+  // Sorted by declination, so each star is only compared against the handful sharing its
+  // parallel — an arcsecond of declination holds one or two of 400 000 stars.
+  const byDec = stars
+    .map((star) => {
+      const distance = Math.hypot(star.x, star.y, star.z);
+      return { star, distance, dec: distance === 0 ? 0 : Math.asin(Math.max(-1, Math.min(1, star.z / distance))) };
+    })
+    .filter((entry) => entry.distance > 0)
+    .sort((a, b) => a.dec - b.dec);
+
+  const cosTolerance = Math.cos(TWIN_TOLERANCE_RAD);
+  let twins = 0;
+  let example = '';
+  for (let i = 0; i < byDec.length; i++) {
+    const a = byDec[i];
+    for (let j = i + 1; j < byDec.length && byDec[j].dec - a.dec <= TWIN_TOLERANCE_RAD; j++) {
+      const b = byDec[j];
+      if (a.star.source === b.star.source) {
+        continue;
+      }
+      const cosine = (a.star.x * b.star.x + a.star.y * b.star.y + a.star.z * b.star.z) / (a.distance * b.distance);
+      if (cosine >= cosTolerance) {
+        twins++;
+        example ||= `${a.star.name} (${a.star.source}) and ${b.star.name} (${b.star.source})`;
+      }
+    }
+  }
+  assertCondition(
+    twins <= MAX_UNMERGED_TWINS,
+    `${twins} stars from different catalogues sit within an arcsecond of each other (at most ${MAX_UNMERGED_TWINS} expected), starting with ${example} — the merge is keeping the same star twice.`
+  );
+  console.log(`  ${survivors} HYG stars have no Gaia counterpart; ${twins} unmerged cross-catalogue pairs within an arcsecond.`);
+}
+
 function validateBodies(bodies: BodyRecord[]): void {
   assertCondition(bodies.length > 0, 'No solar-system bodies were produced.');
 
@@ -161,20 +241,9 @@ async function build(): Promise<void> {
   const deepSky = await fetchDeepSky();
   console.log();
 
-  // The cross-reference depends on the star catalogue as much as on the archive, so it is
-  // resolved again here against whatever catalogue this run produced. A no-op when the two were
-  // fetched together, and the whole point when only one of them was.
-  const rematch = rematchHostStars(exoplanets, stars);
-  console.log(
-    `Cross-referencing exoplanet hosts against ${stars.length} stars...\n` +
-      `  ${rematch.matched}/${rematch.total} matched` +
-      (rematch.resolvable < rematch.total ? ` (${rematch.total - rematch.resolvable} records predate stored host coordinates and kept their existing match)` : '') +
-      (rematch.gained || rematch.lost ? `; ${rematch.gained} gained, ${rematch.lost} lost` : '')
-  );
-  console.log();
-
   console.log('Validating output...');
   validateStars(stars);
+  validateMerge(stars);
   validateBodies(bodies);
   validateExoplanets(exoplanets, new Set(stars.map((star) => star.id)));
   validateDeepSky(deepSky);

tools/etl/fetchExoplanets.ts

@@ -1,3 +1,4 @@
+import { createHash } from 'node:crypto';
 import { writeFileSync } from 'node:fs';
 
 import { buildStarNameIndex, resolveHostStarId } from '../../src/app/shared/astro/host-star-matching';
@@ -15,6 +16,8 @@ const TAP_COLUMNS = [
   'ra',
   'dec',
   'sy_dist',
+  'sy_pmra',
+  'sy_pmdec',
   'pl_orbsmax',
   'pl_orbeccen',
   'pl_orbincl',
@@ -32,9 +35,11 @@ const TAP_COLUMNS = [
 const TAP_QUERY = `select+${TAP_COLUMNS}+from+ps+where+default_flag=1+order+by+pl_name&format=csv`;
 const TAP_URL = `${TAP_BASE_URL}?query=${TAP_QUERY}`;
 
-// A host star match must be within this many parsecs of the catalog position to be
+// The cache is keyed by the request it answers — endpoint included, since the cache records
-// accepted as a cross-reference (guards against coincidental name/position collisions).
+// only that some response arrived: one cached before a column was added would otherwise keep
-const MATCH_TOLERANCE_PC = 0.5;
+// serving rows without it, and a missing proper-motion cell reads as "does not move",
+// silently wrong rather than visibly broken.
+const CACHE_FILE = `exoplanet-archive-ps-${createHash('sha1').update(TAP_URL).digest('hex').slice(0, 8)}.csv`;
 
 /**
  * Downloads confirmed exoplanets from the NASA Exoplanet Archive (`Planetary Systems` TAP
@@ -45,7 +50,7 @@ export async function fetchExoplanets(stars?: StarRecord[]): Promise<ExoplanetRe
   const knownStars = stars ?? (await fetchStars());
   const nameIndex = buildStarNameIndex(knownStars);
 
-  const csv = await fetchTextCached(TAP_URL, 'exoplanet-archive-ps.csv');
+  const csv = await fetchTextCached(TAP_URL, CACHE_FILE);
   const rows = parseCsvObjects(csv);
 
   let matched = 0;
@@ -55,11 +60,12 @@ export async function fetchExoplanets(stars?: StarRecord[]): Promise<ExoplanetRe
     const raDeg = parseOptionalNumber(row['ra']) ?? Number.NaN;
     const decDeg = parseOptionalNumber(row['dec']) ?? Number.NaN;
     const distancePc = parseOptionalNumber(row['sy_dist']) ?? Number.NaN;
+    const pmRaMasPerYear = parseOptionalNumber(row['sy_pmra']);
+    const pmDecMasPerYear = parseOptionalNumber(row['sy_pmdec']);
 
     const hostStarId = resolveHostStarId(
-      { hostname: row['hostname'], raDeg, decDeg, distancePc },
+      { hostname: row['hostname'], raDeg, decDeg, distancePc, pmRaMasPerYear, pmDecMasPerYear },
       knownStars,
-      MATCH_TOLERANCE_PC,
       nameIndex
     );
     if (hostStarId !== null) {
@@ -84,6 +90,8 @@ export async function fetchExoplanets(stars?: StarRecord[]): Promise<ExoplanetRe
       hostRaDeg: parseOptionalNumber(row['ra']),
       hostDecDeg: parseOptionalNumber(row['dec']),
       hostDistancePc: parseOptionalNumber(row['sy_dist']),
+      hostPmRaMasPerYear: pmRaMasPerYear,
+      hostPmDecMasPerYear: pmDecMasPerYear,
       orbit: {
         semiMajorAxisAu: parseOptionalNumber(row['pl_orbsmax']),
         eccentricity: parseOptionalNumber(row['pl_orbeccen']),

tools/etl/fetchSolarSystem.ts

@@ -1,10 +1,14 @@
 import { writeFileSync } from 'node:fs';
 
 import { BodyRecord } from '../../src/app/shared/models/body.model';
+import { gmForParent } from '../../src/app/shared/astro/constants';
+import { orbitalPeriodDays } from '../../src/app/shared/astro/kepler';
 import { SUN_STAR_ID } from '../../src/app/shared/models/star.model';
 import { fetchHorizonsBody } from './lib/horizons';
 import { dataPath, ensureDataDir } from './lib/paths';
 
+const HOURS_PER_DAY = 24;
+
 interface BodySpec {
   id: string;
   name: string;
@@ -12,6 +16,11 @@ interface BodySpec {
   horizonsCommand: string;
   center: string;
   parentBodyId?: string;
+  /**
+   * Obliquity to orbit, in degrees, where the Horizons page states none. Pluto's is from the IAU
+   * WGCCRE 2015 pole (RA 132.99, Dec -6.16), 119.6 degrees: past 90, so it turns retrograde.
+   */
+  obliquityDeg?: number;
 }
 
 // Sun-centered planets/dwarf, then their major moons (planetocentric elements).
@@ -24,7 +33,7 @@ const BODY_SPECS: BodySpec[] = [
   { id: 'saturn', name: 'Saturn', kind: 'planet', horizonsCommand: '699', center: '500@10' },
   { id: 'uranus', name: 'Uranus', kind: 'planet', horizonsCommand: '799', center: '500@10' },
   { id: 'neptune', name: 'Neptune', kind: 'planet', horizonsCommand: '899', center: '500@10' },
-  { id: 'pluto', name: 'Pluto', kind: 'dwarf', horizonsCommand: '999', center: '500@10' },
+  { id: 'pluto', name: 'Pluto', kind: 'dwarf', horizonsCommand: '999', center: '500@10', obliquityDeg: 119.6 },
   { id: 'moon', name: 'Moon', kind: 'moon', horizonsCommand: '301', center: '500@399', parentBodyId: 'earth' },
   { id: 'phobos', name: 'Phobos', kind: 'moon', horizonsCommand: '401', center: '500@499', parentBodyId: 'mars' },
   { id: 'deimos', name: 'Deimos', kind: 'moon', horizonsCommand: '402', center: '500@499', parentBodyId: 'mars' },
@@ -56,6 +65,18 @@ export async function fetchSolarSystem(): Promise<BodyRecord[]> {
       console.warn(`  no physical radius found for ${spec.name}; defaulting to 0.`);
     }
 
+    // Every moon listed here is tidally locked, so its day is its orbit — as drawn, from these
+    // elements and the parent's mass by Kepler. Not every page says so: the Moon's gives a rate,
+    // the true sidereal month, 1.4% off the orbit these elements trace, so its face drifted five
+    // degrees an orbit; Titan's gives nothing, so it did not turn. Taking the orbit keeps one face
+    // towards the parent, which is what synchronous means.
+    const rotationPeriodHours = result.tidallyLocked || spec.kind === 'moon'
+      ? orbitalPeriodDays(result.orbit.semiMajorAxisAu, gmForParent(spec.parentBodyId)) * HOURS_PER_DAY
+      : result.rotationPeriodHours;
+    if (rotationPeriodHours === undefined) {
+      console.warn(`  no rotation period found for ${spec.name}; it will not turn.`);
+    }
+
     bodies.push({
       id: spec.id,
       systemStarId: SUN_STAR_ID,
@@ -63,7 +84,9 @@ export async function fetchSolarSystem(): Promise<BodyRecord[]> {
       kind: spec.kind,
       radiusKm: result.radiusKm ?? 0,
       orbit: result.orbit,
-      ...(spec.parentBodyId ? { parentBodyId: spec.parentBodyId } : {})
+      ...(spec.parentBodyId ? { parentBodyId: spec.parentBodyId } : {}),
+      ...(rotationPeriodHours !== undefined ? { rotationPeriodHours } : {}),
+      ...((result.obliquityDeg ?? spec.obliquityDeg) !== undefined ? { obliquityDeg: result.obliquityDeg ?? spec.obliquityDeg } : {})
     });
   }
 

tools/etl/fetchStars.ts

@@ -1,9 +1,9 @@
 import { writeFileSync } from 'node:fs';
 
-import { raDecDistanceToXyz } from '../../src/app/shared/astro/coordinates';
+import { mergeStarCatalogues, placementDistancePc } from '../../src/app/shared/astro/star-merge';
-import { mergeStarCatalogues } from '../../src/app/shared/astro/star-merge';
 import { encodeStarCatalog } from '../../src/app/shared/models/star-catalog';
 import { StarRecord, SUN_STAR_ID } from '../../src/app/shared/models/star.model';
+import { fetchGaiaDistancesByHip, GaiaAnswerError } from './sources/gaia';
 import { positionalSources } from './sources/registry';
 import { PARALLAX_PRECISION_MAS } from './sources/star-sources';
 import { parseCsvObjects, parseOptionalNumber } from './lib/csv';
@@ -20,13 +20,14 @@ const HYG_UNKNOWN_DISTANCE_PC = 100000; // HYG's placeholder for unmeasured/unre
 const UNKNOWN_MAGNITUDE = 15;
 
 /**
- * Stars within this distance (parsecs) of the Sun are kept for the galaxy view.
+ * Stars either survey places within this distance (parsecs) of the Sun are kept for the galaxy
+ * view; `placementDistancePc` decides which distance a kept star is drawn at.
  *
- * Set at the range HYG's own measurements reach rather than at a round number. 98.6% of its
+ * Set at the range Hipparcos's own measurements reach rather than at a round number: its
- * rows carry a Hipparcos identifier, and Hipparcos parallaxes are good to roughly a
+ * parallaxes are good to roughly a milliarcsecond, so at 250 pc (4 mas) a distance is uncertain
- * milliarcsecond — so at 250 pc (4 mas) a star's distance is uncertain by some tens of per
+ * by some tens of per cent. That is why it is not applied to the Hipparcos distance alone:
- * cent, and beyond it the catalogue is plotting noise. Note that only the *radial* placement
+ * Gaia puts 6 833 of the stars Hipparcos places inside it outside, and 3 666 the other way
- * blurs: a star's direction on the sky stays exact at any distance.
+ * round. Only the *radial* placement blurs; a star's direction on the sky stays exact.
  *
  * The catalogue is also magnitude-limited, so this is not a volume-complete sample beyond about
  * 50 pc: it thins to the intrinsically bright, which is the same selection the naked eye makes.
@@ -59,51 +60,76 @@ function resolveName(row: Record<string, string>): string {
 }
 
 /**
- * Downloads the HYG (Hipparcos/Yale/Gliese) stellar database, converts each star's
+ * Downloads the HYG (Hipparcos/Yale/Gliese) stellar database, places each star along its
- * RA/Dec/distance into galaxy-scale Cartesian coordinates (parsecs), filters by distance,
+ * equatorial direction (epoch J2000.0) at the better of its Hipparcos and Gaia distances, keeps
- * and writes `stars.bin` (packed positions) + `stars-index.json` (everything else).
+ * the ones either survey puts within range, unions the other positional sources, and writes
+ * `stars.bin` (packed positions) + `stars-index.json` (everything else).
  */
 export async function fetchStars(): Promise<StarRecord[]> {
   console.log(`Fetching HYG star catalog (distance cutoff: ${DISTANCE_CUTOFF_PC} pc)...`);
   const csv = await fetchTextCached(HYG_CSV_URL, 'hygdata_v41.csv');
   const rows = parseCsvObjects(csv);
+  // Not skipped when unreachable, unlike the positional sources below; see its own comment.
+  const gaiaPcByHip = await fetchGaiaDistancesByHip();
 
   const stars: StarRecord[] = [];
+  let atGaiaDistance = 0;
+  let pastCutoff = 0;
 
   for (const row of rows) {
     const id = Number(row['id']);
-    const distancePc = Number(row['dist']);
 
     if (id === SUN_STAR_ID) {
       stars.push({ id, name: 'Sol', x: 0, y: 0, z: 0, magnitude: parseOptionalNumber(row['mag']) ?? UNKNOWN_MAGNITUDE, spectralType: row['spect'] || 'G2V', colorIndex: parseOptionalNumber(row['ci']) ?? null });
       continue;
     }
 
-    if (!Number.isFinite(distancePc) || distancePc >= HYG_UNKNOWN_DISTANCE_PC || distancePc > DISTANCE_CUTOFF_PC) {
+    const hygPc = Number(row['dist']);
+    const hipparcosPc = Number.isFinite(hygPc) && hygPc > 0 && hygPc < HYG_UNKNOWN_DISTANCE_PC ? hygPc : undefined;
+    const gaiaPc = row['hip'] ? gaiaPcByHip.get(Number(row['hip'])) : undefined;
+    const distancePc = placementDistancePc(hipparcosPc, gaiaPc, DISTANCE_CUTOFF_PC);
+    if (distancePc === null) {
       continue;
     }
 
-    const raHours = Number(row['ra']);
+    // HYG's own Cartesian columns rather than its `ra`/`dec`, which are in the same frame as
-    const decDeg = Number(row['dec']);
+    // `raDecDistanceToXyz` and would be redundant if the two agreed. They do not, for the stars
-    if (!Number.isFinite(raHours) || !Number.isFinite(decDeg)) {
+    // that move: the right ascension was carried from the Hipparcos epoch to 2000.0 without the
+    // cos δ its motion needs, which puts Proxima 17.9″ from where HYG's own x/y/z — and Gaia,
+    // once brought to the same epoch — have it. 1813 stars differ by over an arcsecond, and the
+    // Cartesian columns are the ones Gaia agrees with for 1155 of them against 156 (one of those,
+    // HIP 57146, has x/y/z 161″ from its own ra/dec and stays double).
+    //
+    // Only their direction is used. They sit at HYG's own distance, or at its 100 000 pc
+    // placeholder where it has none, and are carried along that direction to the one chosen above.
+    const x = Number(row['x']);
+    const y = Number(row['y']);
+    const z = Number(row['z']);
+    const length = Math.hypot(x, y, z);
+    if (![x, y, z].every(Number.isFinite) || length === 0) {
       continue;
     }
-
+    const scale = distancePc / length;
-    const { x, y, z } = raDecDistanceToXyz(raHours, decDeg, distancePc);
+    if (gaiaPc !== undefined) {
+      atGaiaDistance++;
+    }
+    if (distancePc > DISTANCE_CUTOFF_PC) {
+      pastCutoff++;
+    }
 
     stars.push({
       id,
       name: resolveName(row),
-      x,
+      x: x * scale,
-      y,
+      y: y * scale,
-      z,
+      z: z * scale,
       magnitude: parseOptionalNumber(row['mag']) ?? UNKNOWN_MAGNITUDE,
       spectralType: row['spect'] || 'Unknown',
       colorIndex: parseOptionalNumber(row['ci']) ?? null
     });
   }
 
-  console.log(`  kept ${stars.length} stars (of ${rows.length} in the catalog).`);
+  console.log(`  kept ${stars.length} stars (of ${rows.length} in the catalog): ${atGaiaDistance} at Gaia's distance, ${pastCutoff} of them past ${DISTANCE_CUTOFF_PC} pc.`);
 
   const merged = await mergeWithOtherSources(stars);
   merged.sort((a, b) => a.id - b.id);
@@ -114,9 +140,11 @@ export async function fetchStars(): Promise<StarRecord[]> {
 /**
  * Unions HYG with every other positional source that is wired in and reachable.
  *
- * A source that cannot be reached is reported and skipped rather than failing the run. That is
+ * A source that cannot be reached is reported and skipped here rather than thrown, so a run still
- * not defensive padding: the archives this would draw on are frequently unavailable, and a build
+ * gets as far as validation and says what it has. Whether that may be published is decided
- * that produces a smaller catalogue is far better than one that produces none.
+ * there: `validateMerge` in build.ts refuses a catalogue Gaia contributed nothing to. A source
+ * that answered with something unusable ({@link GaiaAnswerError}) is a different matter, and stops
+ * the run where it happened rather than being reported later as an outage.
  */
 async function mergeWithOtherSources(hygStars: StarRecord[]): Promise<StarRecord[]> {
   const others = positionalSources().filter((source) => source.id !== 'hyg');
@@ -134,6 +162,11 @@ async function mergeWithOtherSources(hygStars: StarRecord[]): Promise<StarRecord
         stars: await source.fetch!()
       });
     } catch (error) {
+      // An answer that cannot be worked with is not an outage: skipping it would write a
+      // half-catalogue over the published assets before the merge gate got to say so.
+      if (error instanceof GaiaAnswerError) {
+        throw error;
+      }
       console.log(`  skipping ${source.name}: ${error instanceof Error ? error.message : error}`);
     }
   }
@@ -143,7 +176,7 @@ async function mergeWithOtherSources(hygStars: StarRecord[]): Promise<StarRecord
   }
 
   const { stars, summary } = mergeStarCatalogues(candidates);
-  console.log(`  merged ${summary.total} stars from ${candidates.length} catalogues (${summary.duplicates} duplicates resolved to the better parallax):`);
+  console.log(`  merged ${summary.total} stars from ${candidates.length} catalogues (${summary.duplicates} entries folded into a better-measured one):`);
   for (const [sourceId, count] of Object.entries(summary.bySource)) {
     console.log(`    ${sourceId}: ${count}`);
   }

tools/etl/lib/horizons.ts

@@ -20,6 +20,16 @@ export interface HorizonsQuery {
 export interface HorizonsResult {
   radiusKm?: number;
   orbit: OrbitalElements;
+  /**
+   * Sidereal rotation period in hours, negative where the page gives a negative rate —
+   * Venus and Uranus. Absent where the page publishes none. The same pages also give an obliquity
+   * past 90 degrees for those two, which says the same thing again; see the renderer's spinFor.
+   */
+  rotationPeriodHours?: number;
+  /** Tilt of the rotation axis from the body's own orbital plane, in degrees. */
+  obliquityDeg?: number;
+  /** The page says "Synchronous" instead of a period: its day is its orbit. */
+  tidallyLocked: boolean;
 }
 
 const RADIUS_PATTERNS = [
@@ -30,10 +40,66 @@ const RADIUS_PATTERNS = [
   /Radius\s*\(gravity\),?\s*km\s*=\s*([\d.]+)/i
 ];
 
+/**
+ * How each page states how fast the body turns, in the order they are tried.
+ *
+ * The rate in radians per second is preferred wherever it appears: it is unambiguous and it is
+ * signed: Venus and Uranus carry a negative one. A period in hours or days
+ * comes next, then the sexagesimal form the giant planets use, and finally the word most moons carry
+ * instead of a number, Synchronous. Not all do — the Moon's page gives a rate, Titan's nothing —
+ * so the caller treats every moon it lists as locked whatever its page says.
+ */
+const ROTATION_RATE_PATTERN = /Rot(?:ational)?\.?\s*Rate\s*[(,]\s*rad\/s\s*\)?\s*=\s*(-?[\d.]+)/i;
+const ROTATION_PERIOD_PATTERNS = [
+  /Sid(?:ereal|\.)?\s*rot\.?\s*period[^=]*=\s*(-?[\d.]+)(?:\+-[\d.]+)?\s*(h|hr|hrs|d|day|days)\b/i,
+  /Rotation(?:al)?\s*period[^=]*=\s*(-?[\d.]+)\s*(h|hr|hrs|d|day|days)\b/i
+];
+/** `9h 55m 29.711 s`, as Jupiter and Saturn state it. */
+const SEXAGESIMAL_ROTATION_PATTERN = /Sid(?:ereal|\.)?\s*rot\.?\s*period[^=]*=\s*(\d+)\s*h\s*(\d+)\s*m\s*([\d.]+)\s*s/i;
+const SYNCHRONOUS_PATTERN = /Rotation(?:al)?\s*period\s*=?\s*:?\s*Synchronous/i;
+const OBLIQUITY_PATTERN = /Obliquity\s*to\s*orbit[^=]*=\s*(-?[\d.]+)/i;
+
+const HOURS_PER_DAY = 24;
+const SECONDS_PER_HOUR = 3600;
+
+/**
+ * True where the page gives no number because the body keeps one face to its parent, so its day
+ * is its orbit. The period itself is then Kepler's, which the caller
+ * works out from the elements above and the parent's mass.
+ */
+export function isTidallyLocked(text: string): boolean {
+  return SYNCHRONOUS_PATTERN.test(text);
+}
+
+/** Sidereal rotation period, in hours, from whichever form the page states it in. */
+export function extractRotationPeriodHours(text: string): number | undefined {
+  const rate = text.match(ROTATION_RATE_PATTERN);
+  if (rate && Number(rate[1]) !== 0) {
+    return (2 * Math.PI) / (Number(rate[1]) * SECONDS_PER_HOUR);
+  }
+  const sexagesimal = text.match(SEXAGESIMAL_ROTATION_PATTERN);
+  if (sexagesimal) {
+    return Number(sexagesimal[1]) + Number(sexagesimal[2]) / 60 + Number(sexagesimal[3]) / SECONDS_PER_HOUR;
+  }
+  for (const pattern of ROTATION_PERIOD_PATTERNS) {
+    const match = text.match(pattern);
+    if (match) {
+      const hours = Number(match[1]) * (match[2].toLowerCase().startsWith('d') ? HOURS_PER_DAY : 1);
+      return Number.isFinite(hours) && hours !== 0 ? hours : undefined;
+    }
+  }
+  return undefined;
+}
+
+export function extractObliquityDeg(text: string): number | undefined {
+  const match = text.match(OBLIQUITY_PATTERN);
+  return match ? Number(match[1]) : undefined;
+}
+
 /**
  * Queries JPL Horizons for a body's heliocentric (or planetocentric, for moons) osculating
- * orbital elements plus, when available, its mean physical radius — both in a single
+ * orbital elements plus, when available, its mean physical radius and how it turns — all in a
- * request (`OBJ_DATA=YES` + `EPHEM_TYPE=ELEMENTS`).
+ * single request (`OBJ_DATA=YES` + `EPHEM_TYPE=ELEMENTS`).
  */
 export async function fetchHorizonsBody(query: HorizonsQuery): Promise<HorizonsResult> {
   const url =
@@ -44,7 +110,10 @@ export async function fetchHorizonsBody(query: HorizonsQuery): Promise<HorizonsR
   const text = await fetchTextCached(url, query.cacheKey);
   return {
     radiusKm: extractRadiusKm(text),
-    orbit: extractOrbitalElements(text)
+    orbit: extractOrbitalElements(text),
+    rotationPeriodHours: extractRotationPeriodHours(text),
+    obliquityDeg: extractObliquityDeg(text),
+    tidallyLocked: isTidallyLocked(text)
   };
 }
 

tools/etl/lib/http.ts

@@ -17,17 +17,44 @@ export async function fetchTextCached(url: string, cacheKey: string): Promise<st
   }
 
   console.log(`  fetching ${url}`);
-  const response = await fetch(url);
+  const text = await fetchText(url);
-  if (!response.ok) {
-    throw new Error(`Failed to fetch ${url}: ${response.status} ${response.statusText}`);
-  }
-  const text = await response.text();
 
   mkdirSync(dirname(cachePath), { recursive: true });
   writeFileSync(cachePath, text, 'utf-8');
   return text;
 }
 
+/**
+ * How long to wait before each retry of a failed request. The archives this reads are public
+ * services that time out under load — the Gaia TAP has answered a five-row join in two and a
+ * half minutes and a full one with a 500 — and a weekly refresh that gives up on the first of
+ * those publishes nothing that week.
+ */
+const RETRY_DELAYS_MS = [30_000, 120_000];
+
+async function fetchText(url: string): Promise<string> {
+  for (let attempt = 0; ; attempt++) {
+    let response = await fetch(url).catch((error: unknown) => (error instanceof Error ? error : new Error(String(error))));
+    if (!(response instanceof Error) && response.ok) {
+      // Read inside the loop, because the body is where these downloads fail: the Gaia CSV is
+      // 57 MB, and a connection reset part-way through rejects here, long after the 200.
+      const body = await response.text().catch((error: unknown) => (error instanceof Error ? error : new Error(String(error))));
+      if (typeof body === 'string') {
+        return body;
+      }
+      response = body;
+    }
+    const reason = response instanceof Error ? response.message : `${response.status} ${response.statusText}`;
+    // A 4xx is the request's own fault, and waiting will not change the answer.
+    const retryable = response instanceof Error || response.status >= 500;
+    if (!retryable || attempt >= RETRY_DELAYS_MS.length) {
+      throw new Error(`Failed to fetch ${url}: ${reason}`);
+    }
+    console.log(`  ${reason}; trying again in ${RETRY_DELAYS_MS[attempt] / 1000} s`);
+    await new Promise((resolve) => setTimeout(resolve, RETRY_DELAYS_MS[attempt]));
+  }
+}
+
 /** Convenience wrapper around {@link fetchTextCached} that parses the cached response as JSON. */
 export async function fetchJsonCached<T>(url: string, cacheKey: string): Promise<T> {
   return JSON.parse(await fetchTextCached(url, cacheKey)) as T;

tools/etl/rematchHostStars.ts

@@ -1,18 +0,0 @@
-import { readFileSync, writeFileSync } from 'node:fs';
-
-import { RematchSummary, rematchHostStars } from '../../src/app/shared/astro/host-star-matching';
-import { ExoplanetRecord } from '../../src/app/shared/models/exoplanet.model';
-import { StarRecord } from '../../src/app/shared/models/star.model';
-import { dataPath } from './lib/paths';
-
-/**
- * Reads the written assets, re-resolves every exoplanet's host star against the given catalogue,
- * and writes the exoplanets back. The matching itself lives with the matcher, in
- * `host-star-matching.ts`; this is only the file handling around it.
- */
-export function rematchWrittenAssets(stars: readonly StarRecord[]): RematchSummary {
-  const exoplanets = JSON.parse(readFileSync(dataPath('exoplanets.json'), 'utf8')) as ExoplanetRecord[];
-  const summary = rematchHostStars(exoplanets, stars);
-  writeFileSync(dataPath('exoplanets.json'), JSON.stringify(exoplanets));
-  return summary;
-}

tools/etl/sources/gaia.ts

@@ -1,4 +1,6 @@
-import { raDegDecDistanceToXyz } from '../../../src/app/shared/astro/coordinates';
+import { createHash } from 'node:crypto';
+
+import { propagateProperMotion, raDegDecDistanceToXyz } from '../../../src/app/shared/astro/coordinates';
 import { StarRecord } from '../../../src/app/shared/models/star.model';
 import { parseCsvObjects, parseOptionalNumber } from '../lib/csv';
 import { fetchTextCached } from '../lib/http';
@@ -11,14 +13,24 @@ import { fetchTextCached } from '../lib/http';
  * Galaxy — no catalogue is close to the rest — but within a few hundred parsecs it is complete
  * in a way Hipparcos never was, and its parallaxes are fifty times more precise.
  *
- * **This has never been run.** Every ESA, NOIRLab, SDSS and Euclid endpoint is unreachable from
+ * Written blind against the published DR3 schema, since no ESA endpoint was reachable from the
- * the environment this was written in, so the query below is written against the published DR3
+ * environment it was written in; first run for real by the scheduled refresh of 2026-08-24, which
- * schema and has not been executed against it. Treat the column names as the first thing to
+ * fetched 412 765 rows.
- * check if a real run misbehaves.
  */
 
 const GAIA_TAP_URL = 'https://gea.esac.esa.int/tap-server/tap/sync';
 
+/**
+ * Gaia DR3 gives positions for J2016.0; HYG for J2000.0, which is the epoch this map keeps.
+ * Sixteen years of proper motion is over an arcsecond for anything faster than ~62 mas/yr —
+ * which is most of the nearest stars: 62″ for Proxima, 166″ for Barnard's — so as published, the
+ * two catalogues never agree on where those stars are, and a merge that matched them on the sky
+ * kept every one of them twice. Each position is therefore carried back to J2000.0 with Gaia's
+ * own proper motion before it leaves here.
+ */
+const GAIA_DR3_EPOCH = 2016.0;
+const CATALOGUE_EPOCH = 2000.0;
+
 /**
  * How far out to take Gaia, in parsecs, and the faintest star to keep.
  *
@@ -26,9 +38,12 @@ const GAIA_TAP_URL = 'https://gea.esac.esa.int/tap-server/tap/sync';
  * past anything this map draws, so the limit here is a payload decision: the catalogue is baked
  * into a static asset that a browser downloads before the first frame.
  */
-const DISTANCE_CUTOFF_PC = Number(process.env['ETL_GAIA_DISTANCE_PC'] ?? 250);
+const DEFAULT_DISTANCE_CUTOFF_PC = 250;
-const MAGNITUDE_LIMIT = Number(process.env['ETL_GAIA_MAGNITUDE_LIMIT'] ?? 12);
+const DEFAULT_MAGNITUDE_LIMIT = 12;
-const ROW_LIMIT = Number(process.env['ETL_GAIA_ROW_LIMIT'] ?? 500000);
+const DEFAULT_ROW_LIMIT = 500_000;
+const DISTANCE_CUTOFF_PC = Number(process.env['ETL_GAIA_DISTANCE_PC'] ?? DEFAULT_DISTANCE_CUTOFF_PC);
+const MAGNITUDE_LIMIT = Number(process.env['ETL_GAIA_MAGNITUDE_LIMIT'] ?? DEFAULT_MAGNITUDE_LIMIT);
+const ROW_LIMIT = Number(process.env['ETL_GAIA_ROW_LIMIT'] ?? DEFAULT_ROW_LIMIT);
 
 /**
  * Relative parallax error above which a star is dropped: a parallax measured to worse than 20%
@@ -44,15 +59,46 @@ function parallaxFloorMas(distancePc: number): number {
 function buildQuery(): string {
   return [
     `select top ${ROW_LIMIT}`,
-    'source_id, ra, dec, parallax, parallax_error, phot_g_mean_mag, bp_rp',
+    'source_id, ra, dec, pmra, pmdec, parallax, parallax_error, phot_g_mean_mag, bp_rp',
     'from gaiadr3.gaia_source',
     `where parallax > ${parallaxFloorMas(DISTANCE_CUTOFF_PC).toFixed(6)}`,
     `and parallax_over_error > ${(1 / MAX_PARALLAX_ERROR_RATIO).toFixed(1)}`,
     `and phot_g_mean_mag < ${MAGNITUDE_LIMIT}`,
-    'order by phot_g_mean_mag asc'
+    // source_id breaks the ties — 20 064 groups share a G at the published precision — so the
+    // row order, and with it the ids assigned below, is a pure function of the archive's content.
+    'order by phot_g_mean_mag asc, source_id asc'
   ].join(' ');
 }
 
+/**
+ * How many rows the query above holds when nothing is overridden: 412 765, and DR3 is a finished
+ * data release, so that number only moves when the query does. It lives here, under the query, so
+ * that an edit to any of its filters is made with the count it invalidates in view.
+ *
+ * Checked because a short answer looks exactly like a complete one. The TAP service truncates on
+ * its own timeout and still serves a well-formed CSV with a 200, and the rows are ordered by
+ * magnitude, so what comes back is the bright half — the half HYG overlaps. The merge gate in
+ * `build.ts` would then see Gaia stars present and a survivor count barely moved, and pass a
+ * catalogue missing two hundred thousand stars, which the weekly job would publish and the runner
+ * would cache for the weeks after it. Same failure, and same guard, as
+ * {@link MIN_USABLE_HIP_DISTANCES} below.
+ *
+ * Only checked when nothing is overridden: the environment overrides exist to fetch a smaller
+ * slice on purpose.
+ */
+const DEFAULT_QUERY_ROWS = 412_765;
+const MIN_ROW_SHARE = 0.95;
+
+/**
+ * An answer the archive gave that cannot be worked with, as against an archive that gave none.
+ *
+ * `fetchStars` skips a source it cannot reach and leaves the merge gate to judge the result. That
+ * is right for an outage and wrong for a truncated CSV, which would be skipped, cached, and land
+ * as "the archive was unreachable" long after the assets had been overwritten — so these throws
+ * are marked, and rethrown there.
+ */
+export class GaiaAnswerError extends Error {}
+
 /**
  * Gaia publishes no spectral classifications, but `bp_rp` is a colour index on the same footing
  * as HYG's `ci` — so the app's existing colour and spectral-class handling works unchanged, and
@@ -69,11 +115,29 @@ const UNKNOWN_SPECTRAL_TYPE = 'Unknown';
 const GAIA_ID_BASE = 1_000_000_000;
 
 export async function fetchGaiaStars(): Promise<StarRecord[]> {
-  const url = `${GAIA_TAP_URL}?REQUEST=doQuery&LANG=ADQL&FORMAT=csv&QUERY=${encodeURIComponent(buildQuery())}`;
+  const query = buildQuery();
+  const url = `${GAIA_TAP_URL}?REQUEST=doQuery&LANG=ADQL&FORMAT=csv&QUERY=${encodeURIComponent(query)}`;
   console.log(`Fetching Gaia DR3 (within ${DISTANCE_CUTOFF_PC} pc, G < ${MAGNITUDE_LIMIT}, at most ${ROW_LIMIT} rows)...`);
 
-  const csv = await fetchTextCached(url, 'gaia-dr3.csv');
+  // Keyed by the whole request, so a response cached for other columns, another order, or
+  // another endpoint can never be mistaken for this one — the cache records only that some
+  // response arrived, not what it answered.
+  const cacheKey = `gaia-dr3-${createHash('sha1').update(url).digest('hex').slice(0, 8)}.csv`;
+  const csv = await fetchTextCached(url, cacheKey);
   const rows = parseCsvObjects(csv);
+  const jobsQuery = DISTANCE_CUTOFF_PC === DEFAULT_DISTANCE_CUTOFF_PC && MAGNITUDE_LIMIT === DEFAULT_MAGNITUDE_LIMIT && ROW_LIMIT === DEFAULT_ROW_LIMIT;
+  if (jobsQuery && rows.length < DEFAULT_QUERY_ROWS * MIN_ROW_SHARE) {
+    throw new GaiaAnswerError(
+      `Gaia returned ${rows.length} rows, not the ~${DEFAULT_QUERY_ROWS} this query holds — the answer was cut short, it was an error page ` +
+        `served with a 200, or the query was edited without updating DEFAULT_QUERY_ROWS; delete tools/etl/.cache/${cacheKey} once the archive answers properly`
+    );
+  }
+  // Not gated on `jobsQuery` like the floor above it: the only ways to reach this cap are the
+  // overrides that *widen* the query, and they are exactly when it is worth saying. What it must
+  // not fire on is a deliberately smaller slice, where filling the limit is the whole point.
+  if (ROW_LIMIT >= DEFAULT_ROW_LIMIT && rows.length >= ROW_LIMIT) {
+    throw new GaiaAnswerError(`Gaia returned the query's own ${ROW_LIMIT}-row limit, so it is the limit deciding what the map holds; raise ETL_GAIA_ROW_LIMIT.`);
+  }
   const stars: StarRecord[] = [];
 
   rows.forEach((row, index) => {
@@ -89,7 +153,8 @@ export async function fetchGaiaStars(): Promise<StarRecord[]> {
       return;
     }
 
-    const { x, y, z } = raDegDecDistanceToXyz(raDeg, decDeg, distancePc);
+    const j2000 = propagateProperMotion(raDeg, decDeg, parseOptionalNumber(row['pmra']) ?? 0, parseOptionalNumber(row['pmdec']) ?? 0, CATALOGUE_EPOCH - GAIA_DR3_EPOCH);
+    const { x, y, z } = raDegDecDistanceToXyz(j2000.raDeg, j2000.decDeg, distancePc);
     stars.push({
       id: GAIA_ID_BASE + index,
       name: `Gaia DR3 ${row['source_id']}`,
@@ -106,3 +171,52 @@ export async function fetchGaiaStars(): Promise<StarRecord[]> {
   console.log(`  kept ${stars.length} Gaia stars (of ${rows.length} rows).`);
   return stars;
 }
+
+/**
+ * DR3's Hipparcos cross-match is a fixed table of 99 525 rows, 97 751 of them with a usable
+ * parallax. Far fewer means the answer was an error page served with a 200, or was cut short,
+ * and either would pass for "Gaia does not know these stars" and put every one of them back at
+ * its Hipparcos distance.
+ */
+const MIN_USABLE_HIP_DISTANCES = 90_000;
+
+/**
+ * Gaia's distance for every Hipparcos star it has a usable parallax for, keyed by HIP number.
+ *
+ * Taken from the archive's own cross-match (`hipparcos2_best_neighbour`) rather than from
+ * matching positions here, since Gaia's team made that identification star by star with the
+ * proper motions and photometry in hand. It is deliberately not bounded by distance: the stars
+ * it exists for are the ones Hipparcos put inside the map and Gaia puts outside, which the main
+ * query above never fetches.
+ *
+ * Required rather than best effort. Without it every HYG star falls back to its Hipparcos
+ * distance, the 6 833 that Gaia puts past 250 pc move back inside, and the published map would
+ * flip between the two with the archive's availability.
+ */
+export async function fetchGaiaDistancesByHip(): Promise<Map<number, number>> {
+  const query = [
+    'select top 200000 b.original_ext_source_id as hip, g.parallax, g.parallax_over_error',
+    'from gaiadr3.hipparcos2_best_neighbour b join gaiadr3.gaia_source g on g.source_id = b.source_id'
+  ].join(' ');
+  const url = `${GAIA_TAP_URL}?REQUEST=doQuery&LANG=ADQL&FORMAT=csv&QUERY=${encodeURIComponent(query)}`;
+  console.log('Fetching Gaia DR3 distances for Hipparcos stars (archive cross-match)...');
+  const rows = parseCsvObjects(await fetchTextCached(url, `gaia-dr3-hip-${createHash('sha1').update(url).digest('hex').slice(0, 8)}.csv`));
+
+  const distances = new Map<number, number>();
+  for (const row of rows) {
+    const hip = parseOptionalNumber(row['hip']);
+    const parallaxMas = parseOptionalNumber(row['parallax']);
+    const overError = parseOptionalNumber(row['parallax_over_error']);
+    if (hip !== undefined && parallaxMas !== undefined && parallaxMas > 0 && overError !== undefined && overError > 1 / MAX_PARALLAX_ERROR_RATIO) {
+      distances.set(hip, 1000 / parallaxMas);
+    }
+  }
+  if (distances.size < MIN_USABLE_HIP_DISTANCES) {
+    throw new Error(
+      `the Hipparcos cross-match gave ${distances.size} usable distances (of ${rows.length} rows), not the ~97 751 it holds; ` +
+        'delete tools/etl/.cache/gaia-dr3-hip-*.csv once the archive answers properly'
+    );
+  }
+  console.log(`  ${distances.size} Hipparcos stars have a Gaia distance (of ${rows.length} cross-matched).`);
+  return distances;
+}

tools/etl/sources/registry.ts

@@ -14,7 +14,8 @@ export const STAR_SOURCES: readonly StarSource[] = [
     name: 'HYG database (Hipparcos, Yale Bright Star, Gliese)',
     role: 'positional',
     endpoint: 'https://raw.githubusercontent.com/astronexus/HYG-Database',
-    contributes: 'A complete, named, spectrally classified bright-star catalogue with parallaxes — 68388 stars within 250 pc.',
+    contributes:
+      'A complete, named, spectrally classified bright-star catalogue. Its Hipparcos parallaxes give way to Gaia’s wherever Gaia has a usable one, so its stars sit where the better measurement puts them.',
     unimplementedBecause: null
   },
   {

tsconfig.app.json

@@ -9,6 +9,7 @@
     "src/**/*.ts"
   ],
   "exclude": [
-    "src/**/*.spec.ts"
+    "src/**/*.spec.ts",
+    "src/**/*.worker.ts"
   ]
 }

tsconfig.json

@@ -26,6 +26,9 @@
     },
     {
       "path": "./tsconfig.spec.json"
+    },
+    {
+      "path": "./tsconfig.worker.json"
     }
   ]
 }

tsconfig.worker.json

@@ -0,0 +1,13 @@
+/* To learn more about Typescript configuration file: https://www.typescriptlang.org/docs/handbook/tsconfig-json.html. */
+/* To learn more about Angular compiler options: https://angular.dev/reference/configs/angular-compiler-options. */
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "outDir": "./out-tsc/worker",
+    "lib": ["es2022", "webworker"],
+    "types": []
+  },
+  "include": [
+    "src/**/*.worker.ts"
+  ]
+}