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Draw each HYG star at Gaia's distance, and keep the ones Hipparcos misplaced

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HYG and Gaia were both cut at 250 pc, each on its own distance. A star
Hipparcos put at 200 pc and Gaia at 300 was kept by the first, never
downloaded from the second, and drawn at 200. That is where 83% of the
9 691 mid-magnitude HYG stars without a Gaia counterpart came from, and at
the median Hipparcos had them a third too close. The mirror case, Hipparcos
outside and Gaia inside, dropped the HYG row and left its Gaia entry
anonymous.

Gaia's own Hipparcos cross-match (hipparcos2_best_neighbour, a fixed DR3
table of 99 525 rows) gives a usable Gaia distance for 97 751 of them.
placementDistancePc keeps a star either survey puts inside the cutoff, and
draws every kept star at the better measurement, inside the cutoff or not.
57 121 HYG stars now sit at Gaia's distance. 6 833 of them are past 250 pc:
Zet Per 230 -> 259 pc, 35 Ori 137 -> 330, 44 Cnc 223 -> 613, and the
farthest, HIP 69445, at 8.7 kpc. 3 666 stars that Hipparcos put outside are
now kept, and 3 656 of them give a Gaia entry its name.

The cross-match is required rather than skipped when unreachable. Without
it, every one of those stars would move back to its Hipparcos distance, and
the published map would flip with the archive's availability. The ESA TAP
answered it with a 500 at first and in 102 s on the next try. So fetches
now retry 5xx and network failures twice, after 30 s and 120 s, in the
fetch every source goes through. The refresh job also carries the Gaia DR3
responses from run to run in the Actions cache: the release is frozen, and
a live re-fetch has already reproduced stars.bin byte for byte.

423 651 stars (+10), 61 168 HYG rows folded into Gaia entries (+3 656),
351 597 unnamed designations (-3 656). 10 886 HYG survivors and 23 unmerged
pairs under an arcsecond, both inside the merge gate's ceilings. The same
1 972 exoplanets have a host; KELT-4 A b and MWC 758 c now sit on their
named star.

The HUD's "Radius" becomes "Survey radius": 250 pc is where Gaia is
surveyed to, and no longer the edge of the map.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jxMkwA2rbicdGxHosecYi
This commit is contained in:
Senrokai
2026-09-11 19:07:12 +02:00
co-authored by Claude Opus 5
parent 29d3ddb6ef
commit 4eb61ff58e
12 changed files with 189 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tools/etl/fetchStars.ts
+38 -17
View File
@@ -1,8 +1,9 @@
import { writeFileSync } from 'node:fs';
import { mergeStarCatalogues } from '../../src/app/shared/astro/star-merge';
import { mergeStarCatalogues, placementDistancePc } 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 } from './sources/gaia';
import { positionalSources } from './sources/registry';
import { PARALLAX_PRECISION_MAS } from './sources/star-sources';
import { parseCsvObjects, parseOptionalNumber } from './lib/csv';
@@ -19,13 +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
* rows carry a Hipparcos identifier, and Hipparcos parallaxes are good to roughly a
* milliarcsecond — so at 250 pc (4 mas) a star's distance is uncertain by some tens of per
* cent, and beyond it the catalogue is plotting noise. Note that only the *radial* placement
* blurs: a star's direction on the sky stays exact at any distance.
* Set at the range Hipparcos's own measurements reach rather than at a round number: its
* parallaxes are good to roughly a milliarcsecond, so at 250 pc (4 mas) a distance is uncertain
* by some tens of per cent. That is why it is not applied to the Hipparcos distance alone:
* Gaia puts 6 833 of the stars Hipparcos places inside it outside, and 3 666 the other way
* 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.
@@ -58,27 +60,35 @@ function resolveName(row: Record<string, string>): string {
}
/**
* Downloads the HYG (Hipparcos/Yale/Gliese) stellar database, takes each star's equatorial
* Cartesian position (parsecs, epoch J2000.0), filters by distance, unions the other positional
* sources, and writes `stars.bin` (packed positions) + `stars-index.json` (everything else).
* Downloads the HYG (Hipparcos/Yale/Gliese) stellar database, places each star along its
* equatorial direction (epoch J2000.0) at the better of its Hipparcos and Gaia distances, keeps
* 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;
}
@@ -89,26 +99,37 @@ export async function fetchStars(): Promise<StarRecord[]> {
// 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']);
if (![x, y, z].every(Number.isFinite)) {
const length = Math.hypot(x, y, z);
if (![x, y, z].every(Number.isFinite) || length === 0) {
continue;
}
const scale = distancePc / length;
if (gaiaPc !== undefined) {
atGaiaDistance++;
}
if (distancePc > DISTANCE_CUTOFF_PC) {
pastCutoff++;
}
stars.push({
id,
name: resolveName(row),
x,
y,
z,
x: x * scale,
y: y * scale,
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);