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Carry every body's IAU rotational elements, read from NAIF's kernel of the 2015 report

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bodies.json now holds, for 33 of the 38 bodies, the pole right ascension and declination and the
prime meridian W of the IAU WGCCRE 2015 report (Archinal et al. 2018), with their rates and the
periodic terms. They are read from NAIF's pck00011.tpc, which carries the report in a form a
program can read, periodic terms and their angles included. Hyperion (chaotic), Nereid, Eris,
Haumea and Makemake have no model in the report.

The parser, src/app/shared/astro/rotational-elements.ts, sits beside the other source readers so
the unit suite covers it. It reads data blocks only where \begindata stands alone on a line, as
the kernel's own prose mentions the token mid-sentence. It reads the Fortran exponent (the Moon's
-1.4D-12 d² term) and the degree-2 angles of the Mars system, where Phobos's tidal acceleration
lives. NAIF numbers a small body 2 000 000 past its catalogue number, so Ceres is 2000001.

Periodic terms under 0.01 degrees are left out. 0.01 degrees moves a point by 0.11 px on the
largest body ever drawn (Jupiter at 641 px of radius). That drops 32 terms:
- Mercury: 4 (0.0011 degrees and less)
- the Moon: 8 of 13 (0.0072 and less)
- Mars: 13 (0.00024 and less); its three 0.42-1.59 degree long-period terms stay
- Phobos: 1 (0.0063)
- Jupiter: 5 (0.0022 and less)
- Europa: 1 (0.009)
Kept, among others: Mimas's 44.85-degree libration, Triton's 32-degree precession, Miranda's 4.4
and Phobos's 1.14-degree libration.

build.ts now checks the elements against Horizons on the real catalogue:
- Every body but those five carries elements, and they do not.
- The IAU day, 360 over W's rate, is within 1e-4 of Horizons' period. Measured: at most 1.8e-5
  (Jupiter). Neptune gets a 0.01 ceiling: 0.89 per cent, because the report takes Karkoschka's
  15.9663 h where Horizons keeps Voyager's 16.11.
- The spin axis, the pole turned end for end where W runs backwards, is within 0.1 degrees of
  Horizons' obliquity. Measured: at most 0.058 (Venus, 177.358 against 177.3); Uranus 97.771,
  Pluto 119.610, Earth 23.435.
Full npm run etl passes. Three mutants each fail it on the named check:
- W's sign dropped: "Venus's IAU spin axis is 2.642 degrees".
- Ceres looked up by catalogue number: "Body ceres has no IAU rotational elements".
- W's rate read per century: "Mercury's IAU day ... 3.65e+4".

Nothing is drawn from these yet.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Senrokai
2026-09-24 22:46:14 +02:00
co-authored by Claude Opus 5.5
parent ab7d454db1
commit 1c86584642
7 changed files with 1531 additions and 38 deletions
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tools/etl/fetchSolarSystem.ts
+17 -4
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@@ -5,6 +5,8 @@ import { SUN_STAR_ID } from '../../src/app/shared/models/star.model';
import { fetchHorizonsBody } from './lib/horizons';
import { MeanOrbit, parsePlanetMeanElements, parseSatelliteMeanElements, parseSmallBodyElements } from '../../src/app/shared/astro/mean-elements';
import { fetchPlanetMeanElementsText, fetchSatelliteMeanElementsHtml, fetchSmallBodyAnswer } from './lib/mean-elements';
import { MIN_PERIODIC_TERM_DEG, parsePckRotationalElements } from '../../src/app/shared/astro/rotational-elements';
import { fetchPckText } from './lib/pck';
import { dataPath, ensureDataDir } from './lib/paths';
const HOURS_PER_DAY = 24;
@@ -123,15 +125,17 @@ export const FREELY_SPINNING_MOONS = new Set(BODY_SPECS.filter((spec) => spec.sp
* Writes `bodies.json` for the major planets, the five dwarf planets, and every moon in JPL's
* mean-element table more than 100 km in mean radius — Phoebe, at 106.6, the smallest: JPL's
* mean orbital elements for where they go, or the SBDB's osculating ones where there are none,
* and JPL Horizons for their size and spin. Horizons' osculating elements for the same date come
* back alongside, for `build.ts` to check the mean ones against.
* JPL Horizons for their size and spin, and the IAU's rotational elements for where their poles
* point and which face is where. Horizons' osculating elements for the same date come back
* alongside, for `build.ts` to check the mean ones against.
*/
export async function fetchSolarSystem(): Promise<{ bodies: BodyRecord[]; horizonsOrbits: Map<string, OrbitalElements> }> {
console.log(`Fetching ${BODY_SPECS.length} solar-system bodies from JPL (mean elements, Horizons)...`);
console.log(`Fetching ${BODY_SPECS.length} solar-system bodies from JPL (mean elements, Horizons, NAIF's PCK)...`);
const bodies: BodyRecord[] = [];
const horizonsOrbits = new Map<string, OrbitalElements>();
const planetElements = await fetchPlanetMeanElementsText();
const satelliteElements = await fetchSatelliteMeanElementsHtml();
const pck = await fetchPckText();
const gmById = new Map<string, number | undefined>();
for (const spec of BODY_SPECS) {
@@ -183,6 +187,14 @@ export async function fetchSolarSystem(): Promise<{ bodies: BodyRecord[]; horizo
if (rotationPeriodHours === undefined) {
console.warn(` no rotation period found for ${spec.name}; it will not turn.`);
}
// NAIF numbers a small body 2 000 000 past its catalogue number: Ceres, "1;" to Horizons, is 2000001.
const naifId = spec.horizonsCommand.endsWith(';') ? 2_000_000 + Number.parseInt(spec.horizonsCommand, 10) : Number(spec.horizonsCommand);
const rotation = parsePckRotationalElements(pck, naifId);
if (!rotation) {
console.warn(` no IAU rotational elements for ${spec.name}; its pole and meridian are not known.`);
} else if (rotation.skippedDeg.length > 0) {
console.log(` ${spec.name}: ${rotation.skippedDeg.length} periodic terms under ${MIN_PERIODIC_TERM_DEG} degrees left out, the largest ${Math.max(...rotation.skippedDeg)}.`);
}
bodies.push({
id: spec.id,
@@ -197,7 +209,8 @@ export async function fetchSolarSystem(): Promise<{ bodies: BodyRecord[]; horizo
...(spec.parentBodyId ? { parentBodyId: spec.parentBodyId } : {}),
...(parentGm !== undefined ? { massRatio: result.gmKm3PerS2! / parentGm } : {}),
...(rotationPeriodHours !== undefined ? { rotationPeriodHours } : {}),
...((result.obliquityDeg ?? spec.obliquityDeg) !== undefined ? { obliquityDeg: result.obliquityDeg ?? spec.obliquityDeg } : {})
...((result.obliquityDeg ?? spec.obliquityDeg) !== undefined ? { obliquityDeg: result.obliquityDeg ?? spec.obliquityDeg } : {}),
...(rotation ? { rotationalElements: rotation.elements } : {})
});
}