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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
Download Patch File Download Diff File Expand all files Collapse all files
tools/etl/build.ts
+65 -1
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@@ -1,8 +1,9 @@
import { statSync } from 'node:fs';
import { BodyRecord, OrbitalElements } from '../../src/app/shared/models/body.model';
import { eclipticToEquatorial, laplacePlaneToEquatorial } from '../../src/app/shared/astro/coordinates';
import { eclipticToEquatorial, laplacePlaneToEquatorial, raDecToUnitVector } from '../../src/app/shared/astro/coordinates';
import { meanElementsAt, positionAtEpoch } from '../../src/app/shared/astro/kepler';
import { orientationAt } from '../../src/app/shared/astro/rotational-elements';
import { DeepSkyRecord } from '../../src/app/shared/models/deepsky.model';
import { ExoplanetRecord } from '../../src/app/shared/models/exoplanet.model';
import { StarRecord, SUN_STAR_ID } from '../../src/app/shared/models/star.model';
@@ -146,6 +147,7 @@ function validateMerge(stars: StarRecord[]): void {
const MAX_PLANET_OFFSET_DEG = 0.25;
const MAX_MOON_OFFSET_DEG = 2.5;
const KM_PER_AU = 149597870.7;
const DEG_TO_RAD = Math.PI / 180;
/**
* The moons whose table row cannot come within that, each for a reason no mean ellipse carries,
@@ -163,6 +165,33 @@ const KM_PER_AU = 149597870.7;
*/
const MOON_OFFSET_CEILINGS_DEG: Record<string, number> = { mimas: 46, hyperion: 21, iapetus: 11, nereid: 3 };
/**
* The bodies the IAU WGCCRE 2015 report gives no rotational elements for: Hyperion tumbles, and
* Nereid, Eris, Haumea and Makemake have no model. Every other body must carry them, or the
* kernel was read wrongly and the body would be drawn on an invented pole.
*/
const WITHOUT_ROTATIONAL_ELEMENTS = new Set(['hyperion', 'nereid', 'eris', 'haumea', 'makemake']);
/**
* 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.
*/
const MAX_DAY_OFFSET = 1e-4;
const DAY_OFFSET_CEILINGS: Record<string, number> = { neptune: 0.01 };
/**
* How far the tilt of the IAU's spin axis from the orbit may be from the obliquity Horizons
* states. The axis is the IAU's pole, turned end for end where W runs backwards: the report names
* a planet's north pole by the side of the solar system it lies on, whichever way the planet turns.
* Measured on this catalogue: at most 0.058 degrees (Venus, 177.358 against 177.3). Taken as the
* pole alone, Venus comes out at 2.6 degrees and Uranus at 82.2, which is what this catches.
*/
const MAX_OBLIQUITY_OFFSET_DEG = 0.1;
function angleBetweenDeg(a: { x: number; y: number; z: number }, b: { x: number; y: number; z: number }): number {
const cosine = (a.x * b.x + a.y * b.y + a.z * b.z) / (Math.hypot(a.x, a.y, a.z) * Math.hypot(b.x, b.y, b.z));
return (Math.acos(Math.min(1, Math.max(-1, cosine))) * 180) / Math.PI;
@@ -175,6 +204,7 @@ function validateBodies(bodies: BodyRecord[], horizonsOrbits: Map<string, Orbita
assertCondition(ids.size === bodies.length, 'Duplicate body ids were found.');
const offsets: string[] = [];
const spins: string[] = [];
for (const body of bodies) {
const orbitValues = Object.values(body.orbit);
assertCondition(orbitValues.every(Number.isFinite), `Body ${body.id} has non-finite orbital elements.`);
@@ -196,6 +226,39 @@ function validateBodies(bodies: BodyRecord[], horizonsOrbits: Map<string, Orbita
// A radius of 0 is what a page whose radius no pattern reads comes out as — Charon's did.
assertCondition(body.radiusKm > 0, `Body ${body.id} has no radius; its page states it in a form the ETL does not read.`);
const rotation = body.rotationalElements;
assertCondition(
(rotation === undefined) === WITHOUT_ROTATIONAL_ELEMENTS.has(body.id),
`Body ${body.id} ${rotation ? 'has' : 'has no'} IAU rotational elements, which the report ${rotation ? 'does not give' : 'gives'} for it.`
);
if (rotation) {
const rate = rotation.primeMeridianDeg[1];
if (body.rotationPeriodHours !== undefined) {
const dayOffset = Math.abs(((360 / Math.abs(rate)) * 24) / Math.abs(body.rotationPeriodHours) - 1);
const dayCeiling = DAY_OFFSET_CEILINGS[body.id] ?? MAX_DAY_OFFSET;
assertCondition(
dayOffset <= dayCeiling,
`${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 ${dayCeiling} expected).`
);
spins.push(`${body.id} day ${dayOffset.toExponential(1)}`);
}
if (body.obliquityDeg !== undefined) {
const pole = orientationAt(rotation, horizons!.epochJd);
const pointing = raDecToUnitVector(pole.poleRaDeg / 15, pole.poleDecDeg);
const axis = { x: Math.sign(rate) * pointing.x, y: Math.sign(rate) * pointing.y, z: Math.sign(rate) * pointing.z };
const { inclinationDeg, longitudeOfAscendingNodeDeg } = meanElementsAt(body.orbit, body.rates, horizons!.epochJd);
const tilt = inclinationDeg * DEG_TO_RAD;
const node = longitudeOfAscendingNodeDeg * DEG_TO_RAD;
const normal = { x: Math.sin(tilt) * Math.sin(node), y: -Math.sin(tilt) * Math.cos(node), z: Math.cos(tilt) };
const obliquity = angleBetweenDeg(axis, body.laplacePole ? laplacePlaneToEquatorial(normal, body.laplacePole) : eclipticToEquatorial(normal));
assertCondition(
Math.abs(obliquity - body.obliquityDeg) <= MAX_OBLIQUITY_OFFSET_DEG,
`${body.name}'s IAU spin axis is ${obliquity.toFixed(3)} degrees from its orbit's pole, where Horizons gives an obliquity of ${body.obliquityDeg} (at most ${MAX_OBLIQUITY_OFFSET_DEG} apart expected) — the pole or the sense of W was read wrongly.`
);
spins.push(`${body.id} tilt ${obliquity.toFixed(3)}`);
}
}
if (body.kind === 'moon') {
const parent = bodies.find((candidate) => candidate.id === body.parentBodyId);
assertCondition(parent !== undefined, `Moon ${body.id} has no valid parentBodyId.`);
@@ -233,6 +296,7 @@ function validateBodies(bodies: BodyRecord[], horizonsOrbits: Map<string, Orbita
const dwarfCount = bodies.filter((body) => body.kind === 'dwarf').length;
assertCondition(dwarfCount === 5, `Expected the IAU's 5 dwarf planets, found ${dwarfCount}.`);
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(', ')}.`);
}
function validateExoplanets(exoplanets: ExoplanetRecord[], starIds: Set<number>): void {