Correct what the ETL, the code and the textures README said of their own sources and figures

- The IAU day check said it compared W with the period Horizons states. That holds for the eight planets and Phoebe only. Pluto's and Ceres's periods are the IAU's own rate restated (8.5e-12 and 3.3e-10: Horizons' Pluto period is 360 over its W, and the SBDB notes it derived Ceres's from the report's 952.1532 degrees a day), and the 22 locked moons' is their orbit's, from JPL's table, not from their Horizons pages ("Synchronous" on eighteen, nothing on Titan's or Proteus's), and now their W's own rate. The comment, the log line and the error message say which is which; the log shows 0.0e+0 for the twenty locked moons turned at their orbit's rate, 1.1e-8 and 3.1e-7 for the Moon and Phobos. BodyRecord.rotationPeriodHours says that where a source states no period, or one a later measurement overturns, it is the one the ETL spec carries (Nereid's, Eris's), where the previous commit had Eris among the bodies whose source states none. - Phoebe's spec justified its period by a note in the satellite table, which is about another source (Jacobson 2000, Jupiter's outer moons) and says the table carries corrected values. The row's n is right as the table defines it, the rate of the mean longitude: n less twice the node's rate is 0.6541855 degrees a day, against 360 / 550.30391 = 0.6541840. What made Phoebe drift is that the propagator reads a retrograde moon's n as its sidereal rate, as Triton's row gives it. The comment now says so; the period, 550.30391 days, is kept. - body-orientation.ts and its spec said the IAU's W for Earth, "taken at UT", left its face 2.3 and 4.5 degrees off Horizons at AD 1000 and AD 1. The old code took it at UT + 69.184 s; those are that figure's, and at UT itself they are 2.0 and 4.2, as three reviewers measured through the code (4.25, 4.25 and 4.28 at AD 1). - The renderer said the 28 maps entering the Sun's system are about 20 megapixels of JPEG. Read from their frame headers: 37.75, nine at 2048 by 1024 with the Sun's, Jupiter's at 3840 by 1920 and eighteen smaller. - The textures README gave Titan 0.02 per cent unmapped, counting only the source's zeros. Its largest gap is a flat grey of the source's own (147 and 148, its two commonest values), which NASA's caption for PIA19658 names as the gap in coverage: measured on titan.jpg, one region of 1.09 per cent of the pixels, 0.87 of the sphere, at 48-68 N and 37 W to 25 E. The row says 1.1 per cent and where, and step 1 says how it is counted; commit 302fa96's "the rest under 0.2%" is therefore not true of Titan. No behaviour changes but the ETL's log and error wording; the solar ETL passes with the new text. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
2026-09-30 16:16:53 +02:00
parent dadae7b8ca
commit a15a46c617
7 changed files with 45 additions and 23 deletions
@@ -204,7 +204,8 @@ function reshapeOrbitLine(line: THREE.Line, elements: OrbitalElements): void {
 * A photograph is handed to `deferPhotograph`, which puts it on the body once it has loaded, one a
 * frame: a texture is copied to the GPU in the first frame that draws it, and the 28 maps, which
 * arrive within 40 ms of each other, made that one frame a 160-210 ms task on entering the Sun's
- * system (copyExternalImageToTexture, about 20 megapixels of JPEG).
+ * system (copyExternalImageToTexture, about 38 megapixels of JPEG: nine maps at 2048 by 1024, the
+ * Sun's among them, Jupiter's at 3840 by 1920, and eighteen smaller).
 *
 * Every marker is the one unit sphere, {@link MARKER_SPHERE}, scaled to the body's radius, which
 * it also keeps as `userData.radiusAu`: built one a body, the 38 spheres of the Sun's system took
@@ -95,10 +95,10 @@ export interface BodyRecord {
   * 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.
   *
-   * For a locked moon the period is its orbit's, from the mean motion that carries it round; for
-   * a body whose source states none, the measured one its ETL spec carries (Eris, Nereid). Absent
-   * only for Hyperion, which tumbles — the view leaves it still rather than spinning it at an
-   * invented rate.
+   * For a locked moon the period is its orbit's, from the mean motion that carries it round. Where
+   * the source states none, or one a later measurement overturns, it is the one the body's ETL spec
+   * carries: Nereid's K2 light curve, Eris's lock to Dysnomia. Absent only for Hyperion, which
+   * tumbles — the view leaves it still rather than spinning it at an invented rate.
   */
  rotationPeriodHours?: number;
  obliquityDeg?: number;
@@ -50,7 +50,7 @@ describe('bodyPageView', () => {
  it('lights Earth’s face where Horizons does at the far end of the clock too: AD 1000 and AD 1', () => {
    // Horizons' sub-solar longitude from the Sun (observer quantity 14, TIME_TYPE=UT), Earth taken
    // one light-time back: 1.0510 E on JD 2086455 and 1.5606 E on JD 1721600. The IAU's W, taken at
-    // UT, drew them 2.3 and 4.5 degrees west of that.
+    // UT + 69.184 s as it was, drew them 2.3 and 4.5 degrees west of that (2.0 and 4.2 at UT itself).
    for (const [jdUt, lightMinutes, eastDeg] of [[2086455, 8.45437443, 1.05101], [1721600, 8.45020842, 1.560644]]) {
      expect(Math.abs(subSolarPoint(EARTH, jdUt - lightMinutes / 1440).eastDeg - eastDeg)).toBeLessThan(0.15);
    }
@@ -58,8 +58,9 @@ export function poleFrame(pole: { raDeg: number; decDeg: number }, target = new
 * it is turned by the IERS Earth Rotation Angle at the clock's date (IERS Conventions 2010, eq.
 * 5.15), counted from the node its W starts at, 90 degrees past its pole's right ascension. The
 * IAU's W for Earth, fitted to today, runs 6.3e-6 degrees a day slow of that once its pole's drift
- * is counted: taken at UT, it left Earth's lit face 2.3 degrees off Horizons at AD 1000 and 4.5 at
- * AD 1. Taken at TDB, it would have turned ΔT further, 44 degrees at AD 1.
+ * is counted: taken at UT + 69.184 s, as it was, it left Earth's lit face 2.3 degrees off Horizons at
+ * AD 1000 and 4.5 at AD 1 (2.0 and 4.2 at UT itself). Taken at TDB, it would have turned ΔT further,
+ * 44 degrees at AD 1.
 */
 export function bodyOrientation(elements: RotationalElements, jdUtc: number, target = new THREE.Quaternion(), followsUt = false): THREE.Quaternion {
  const { poleRaDeg, poleDecDeg, primeMeridianDeg } = orientationAt(elements, tdbFromUtc(jdUtc));
@@ -32,7 +32,11 @@ Each was downloaded from the URL below and processed the same way (script:
 `build_maps.py`, kept with the measurements outside the repository):

 1. Pixels the source leaves unmapped (value 0 in every band, its no-data value) are set to one
-   flat grey: the mean of the mapped surface. They are never filled with invented terrain.
+   flat grey: the mean of the mapped surface. They are never filled with invented terrain. Titan's
+   source marks its largest gap another way, with a flat grey of its own (147 and 148, its two
+   commonest values; "the uniform gray area in the northern hemisphere indicates a gap in the
+   imaging coverage", PIA19658), which the table counts as unmapped too: 1.09% of `titan.jpg`'s
+   pixels, 0.87% of the sphere, where its zeros alone were 0.02%.
 2. Downsampled by area averaging (PIL `BOX`) to 2 048 by 1 024 for bodies over 1 000 km in radius
   and 1 024 by 512 for the rest.
 3. Rolled half a turn where the source is centred on longitude 180, so longitude 0 is in the
@@ -66,7 +70,7 @@ photometry.
 | `tethys.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Tethys_Cassini_mosaic_global_293m.tif) Tethys Cassini Global Mosaic 293 m | Cassini ISS; NASA/JPL/Space Science Institute | Odysseus, Penelope | 0.04% | 0.009% | 1024x512, 182 KB |
 | `dione.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Dione_Cassini_Voyager_mosaic_global_154m.tif) Dione Cassini-Voyager Global Mosaic 154 m | Cassini ISS and Voyager; NASA/JPL/Space Science Institute | Creusa, Evander | 0.18% | 0.011% | 1024x512, 195 KB |
 | `rhea.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Rhea_Cassini_Voyager_mosaic_global_417m.tif) Rhea Cassini-Voyager Global Mosaic 417 m | Cassini ISS and Voyager; NASA/JPL/Space Science Institute | Inktomi, Tirawa | 0% | 0.003% | 1024x512, 128 KB |
-| `titan.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Titan_ISS_P19658_Mosaic_Global_4km.tif) Titan Cassini ISS Global Mosaic 4 km (938 nm, through the haze) | Cassini ISS; NASA/JPL-Caltech/SSI | Xanadu, Shangri-La, Belet | 0.02% | 0.078% | 2048x1024, 294 KB |
+| `titan.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Titan_ISS_P19658_Mosaic_Global_4km.tif) Titan Cassini ISS Global Mosaic 4 km (938 nm, through the haze) | Cassini ISS; NASA/JPL-Caltech/SSI | Xanadu, Shangri-La, Belet | 1.1% (48-68 N, 37 W to 25 E: the source's own flat grey, see step 1) | 0.078% | 2048x1024, 294 KB |
 | `iapetus.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Iapetus_Cassini_Voyager_mosaic_global_783m.tif) Iapetus Cassini-Voyager Global Mosaic 783 m | Cassini ISS and Voyager; NASA/JPL/Space Science Institute | Cassini Regio (leading side, 90 W), Engelier | 0% | 0.019% | 1024x512, 159 KB |
 | `phoebe.jpg` | [PDS](https://planetarydata.jpl.nasa.gov/img/data/carto/coiss_3001/extras/full/images/SP_1M_0_0_SIMP.IMG.png) COISS_3001, Cassini ISS cartographic map of Phoebe | Cassini ISS; DLR and FU Berlin (Roatsch et al.), NASA PDS | Jason (16 N, 318 W) | 20.41% (the north) | 0.344% (shadows) | 1024x512, 78 KB |
 | `triton.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Triton_Voyager2_ClrMosaic_GlobalFill_600m.tif) Triton Voyager 2 Global Colour Mosaic 600 m (PIA18668) | Voyager 2; P. Schenk, NASA/JPL/LPI | Leviathan Patera; southern cap | 38.59% (the north Voyager 2 never saw) | 0% | 2048x1024, 205 KB |
@@ -212,12 +212,24 @@ const WITHOUT_ROTATIONAL_ELEMENTS = new Set(['hyperion', 'nereid', 'eris', 'haum
 const TUMBLING = new Set(['hyperion']);

 /**
- * How far the IAU's day, 360 degrees over W's rate, may be from the one Horizons states, as a
- * fraction of it. Measured on this catalogue: at most 1.8e-5 (Jupiter's System III, 9.92492 hours
- * against 9.92510). Neptune is 0.89 per cent out, because the report takes 15.9663 hours from the
- * cloud features Karkoschka (2011) tracked, where Horizons keeps Voyager's radio period, 16.11. What
- * this catches is a rate read in the wrong unit or for the wrong body: Oberon's day for Titania's is
- * 55 per cent out.
+ * How far the IAU's day, 360 degrees over W's rate, may be from the period the body's record
+ * carries, as a fraction of it. That period is not always a second source:
+ *
+ * - The eight planets and Phoebe: the one Horizons states. Measured on this catalogue: at most
+ *   1.8e-5 (Jupiter's System III, 9.92492 hours against 9.92510). Neptune is 0.89 per cent out,
+ *   because the report takes 15.9663 hours from the cloud features Karkoschka (2011) tracked, where
+ *   Horizons keeps Voyager's radio period, 16.11.
+ * - Pluto and Ceres: the IAU's own rate restated. Horizons' 153.29335198 hours for Pluto is 360 over
+ *   its W (8.5e-12), and the SBDB's 9.074170 for Ceres, which Horizons prints too, is noted as
+ *   derived from the report's 952.1532 degrees a day (3.3e-10).
+ * - The 22 locked moons: their orbit's period, from JPL's satellite table, not a figure from their
+ *   Horizons pages ("Synchronous" on eighteen of them, nothing on Titan's or Proteus's). Their W is
+ *   turned at that rate (see `lockedToOrbit`, which first holds the kernel's own rate to it within
+ *   1e-5), so here they are 0, but for the Moon and Phobos, whose W keeps its own rate and its
+ *   quadratic (1.1e-8 and 3.1e-7).
+ *
+ * What this catches is a rate read in the wrong unit or for the wrong body: Oberon's day for
+ * Titania's is 55 per cent out.
 */
 const MAX_DAY_OFFSET = 1e-4;
 const DAY_OFFSET_CEILINGS: Record<string, number> = { neptune: 0.01 };
@@ -347,7 +359,7 @@ function validateBodies(bodies: BodyRecord[], horizonsOrbits: Map<string, Orbita
        const dayCeiling = DAY_OFFSET_CEILINGS[body.id] ?? MAX_DAY_OFFSET;
        assertCondition(
          dayOffset <= dayCeiling,
-          `${body.name}'s IAU day, ${((360 / Math.abs(rate)) * 24).toFixed(5)} hours, is ${dayOffset.toExponential(2)} of its length from Horizons' ${Math.abs(body.rotationPeriodHours).toFixed(5)} (at most ${dayCeiling} expected).`
+          `${body.name}'s IAU day, ${((360 / Math.abs(rate)) * 24).toFixed(5)} hours, is ${dayOffset.toExponential(2)} of its length from the ${Math.abs(body.rotationPeriodHours).toFixed(5)} its record carries (at most ${dayCeiling} expected).`
        );
        spins.push(`${body.id} day ${dayOffset.toExponential(1)}`);
      }
@@ -419,7 +431,7 @@ function validateBodies(bodies: BodyRecord[], horizonsOrbits: Map<string, Orbita
    `Eris turns once in ${erisDays.toFixed(3)} days; it is locked to Dysnomia's 15.786-day orbit — the SBDB's 25.9-hour period, which it flags as possibly 30 per cent wrong, was taken.`
  );
  console.log(`  mean elements against Horizons, degrees: ${offsets.join(', ')}.`);
-  console.log(`  IAU rotation against Horizons (day as a fraction of it, tilt in degrees): ${spins.join(', ')}.`);
+  console.log(`  IAU rotation against each record's day and tilt (see MAX_DAY_OFFSET for where each comes from; day as a fraction of it, tilt and a locked moon's face in degrees): ${spins.join(', ')}.`);
 }

 function validateExoplanets(exoplanets: ExoplanetRecord[], starIds: Set<number>): void {
@@ -137,11 +137,15 @@ const BODY_SPECS: BodySpec[] = [
  // Hyperion's eccentricity is 0.105 in JPL's current table (ssd.jpl.nasa.gov/sats/elem, SAT441).
  { id: 'hyperion', name: 'Hyperion', kind: 'moon', horizonsCommand: '607', center: '500@699', parentBodyId: 'saturn', spinsFreely: true, measuredEccentricity: 0.105, trackStepDays: 1 },
  { id: 'iapetus', name: 'Iapetus', kind: 'moon', horizonsCommand: '608', center: '500@699', parentBodyId: 'saturn', poleFollowsOrbit: true },
-  // Phoebe's row gives a mean motion of 0.6569114 degrees a day, a 548.02-day year, where its
-  // Horizons page and JPL's current table (SAT441) give 550.30: the table's own note warns that
-  // its source misstated the mean motions of retrograde moons. On the row's figure Phoebe was
-  // 25 degrees from Horizons by 2025 and 100 by 2075; on the current period, within 2.6 from 1950
-  // to 2100 (2.58 in 1969).
+  // Phoebe's row gives n = 0.6569114 degrees a day as the table defines it, the rate of its mean
+  // longitude, node plus periapsis plus mean anomaly, and its P, 548.02 days, is 360 over that. Its
+  // sidereal period is 550.30 (its Horizons page and JPL's current table, SAT441): n less twice its
+  // node's rate, 0.6541855, against 360 / 550.30391 = 0.6541840. Triton's row gives its sidereal
+  // rate as n instead, and the propagator reads a retrograde moon's n as that (see
+  // `meanElementsAt`): on the row's n Phoebe ran twice its node's rate too fast, 25 degrees from
+  // Horizons by 2025 and 100 by 2075. On the sidereal period it is within 2.6 from 1950 to 2100
+  // (2.58 in 1969). The table's note on misstated retrograde mean motions is about another source,
+  // Jacobson 2000 on Jupiter's outer moons, and says the table carries the corrected values.
  { id: 'phoebe', name: 'Phoebe', kind: 'moon', horizonsCommand: '609', center: '500@699', parentBodyId: 'saturn', spinsFreely: true, periodDays: 550.30391 },
  { id: 'miranda', name: 'Miranda', horizonsCommand: '705', ...URANUS_MOON },
  { id: 'ariel', name: 'Ariel', horizonsCommand: '701', ...URANUS_MOON },