Draw four moons' nodes at JPL's current rates, which Horizons and the IAU's poles agree with

The archived satellite table the moons are read from gives older node
periods than JPL's current one for Miranda (17.727 years against URA182's
17.787), Ganymede (132.654 against 137.812), Callisto (338.82 against
577.264) and Titan (704.60 against 687.370), and 74ea1d6 turned the IAU's
poles after those older rates, taking them for the right ones. They were
not: fitted to Horizons' osculating elements on Uranus's equator over
1601-2399, Miranda's node turns 2023.97 degrees a century (rms 0.04),
against the current table's 2023.95, the IAU's U11 2024.22 and the row's
2030.80. That commit moved Miranda's axis from 0.38 to 2.36 degrees of
Horizons' orbit normal. Mimas's node, 0.986 years in both tables, now takes
the IAU's S3, 36505.5 degrees a century, 1.2 from a Horizons fit where
the row's is 4.5.

The ETL spec carries the node period (nodePeriodYears), and the periapsis
keeps the row's longitude rate: the row gives the longitude's rate (Callisto
68.7 degrees a century, the current table 67.2), so the argument takes up
the change. On the row's argument Callisto's periapsis moved 44 degrees by
2100 and it strayed 0.71 degrees from Horizons over 1950-2100.

Worst angle from Horizons' osculating orbit normal (ICRF), HEAD then now:
- Miranda, 1601-2399: drawn orbit 2.11 -> 0.12, axis 2.36 -> 0.34.
- Mimas, 1750-2249: orbit 0.33 -> 0.11, axis 0.65 -> 0.40.
- Ganymede, 1600-2199: orbit 0.17 -> 0.11, axis 0.13 -> 0.01.
- Callisto, 1600-2199: orbit 0.53 -> 0.20, axis 0.02 -> 0.03.
- Titan, 1750-2249: orbit 0.048 -> 0.052.
Against the 1950-2100 Horizons tracks the ETL checks: Callisto 0.19 -> 0.08,
Miranda 1.73 -> 1.62, Ganymede 0.30 -> 0.29, Mimas 7.43 -> 7.42, Titan 0.06.

lockedToOrbit now barely moves the IAU's node terms: Miranda's U11 to
-2023.95, Ganymede's J5 to 261.23 (262.1), Mimas's S3 not at all, and
Callisto's J6, 3.1 per cent from its new node rate, to 62.36 (64.3), which
takes Callisto's axis from 0.56 to 0.22 degrees of its drawn orbit.

With the drawn rates right, leaving every node term at the IAU's rate no
longer failed the ETL (Mimas used to), nor did a 1 per cent tolerance, the
node's angle without its harmonics, or the older node periods. The axis
ceiling is now 0.25 degrees for Europa (0.13 measured), Ganymede (0.16),
Callisto (0.22), Rhea (0.17), Miranda (0.23) and Triton (0.15), and
Callisto's track ceiling 0.15 (0.08). Guarded mutants, each through the
solar ETL on the real catalogue and then the suite on the bodies.json it
wrote:
- node terms left at the IAU's rates: ETL "europa's spin axis leans up to
  0.33"; suite fails only 'turns the poles of Europa, Ganymede, Callisto,
  Rhea, Miranda and Triton round with their drawn nodes'.
- tolerance 1 per cent: ETL, Callisto 0.33; the same test, alone.
- harmonics dropped: ETL, Triton 0.29 (the suite's three dates miss it).
- the archived node periods: ETL, Callisto's track 0.19; the suite fails
  that test and 'draws Miranda's orbit, and turns its axis, where Horizons
  has its orbit in 1601 and 2390' (orbit 2.02, axis 2.36 at 1601).
- the row's argument kept: ETL, Callisto's track 0.71.

The docs that called the IAU's rates the wrong ones are corrected
(lockedToOrbit, the axis ceiling in build.ts, whose Titan node now turns
in 687 years), and the README and BodyRecord doc no longer say every
locked moon's node terms are re-rated: only those within 5 per cent of a
multiple of the node's rate, never the Moon's or Phobos's, and not the
circles Ariel's, Umbriel's, Titania's and Oberon's poles go round on
(0.36 to 0.50 degrees off their orbits). The README also names the five
bodies the IAU's elements do not turn. Unit suite 866 passed.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
This commit is contained in:
2026-09-30 19:22:57 +02:00
co-authored by Claude Opus 5.5
parent ac23496b37
commit 24c7be1bae
7 changed files with 182 additions and 68 deletions
+9 -5
View File
@@ -55,10 +55,14 @@ in it is measured and what is not.
**System view** — selecting a star flies the camera continuously into its system rather than
cutting to a new scene. The Sun gets the real solar-system bodies, moving on JPL's mean orbital
elements — Standish's for the planets, JPL SSD's satellite table for the moons, the Small-Body
Database for Ceres, Eris, Haumea and Makemake — and turned by the IAU's rotational elements, Earth
by the IERS Earth Rotation Angle; a tidally locked moon's prime meridian (but the Moon's and
Phobos's) turns at its JPL mean motion and its pole's terms on its node at its JPL node rate, both
re-phased to the IAU's values on 2025-01-01, and Iapetus's pole follows its orbit normal
Database for Ceres, Eris, Haumea and Makemake — and turned by the IAU's rotational elements
(Eris, Haumea, Makemake and Nereid, which have none, at their measured days about their orbit
normals, and Hyperion, which tumbles, not at all), Earth by the IERS Earth Rotation Angle; a
tidally locked moon's prime meridian turns at its JPL mean motion, and its pole's terms that turn
within 5 per cent of a multiple of its node's rate at that multiple of its JPL node rate, both
re-phased to the IAU's values on 2025-01-01 (the Moon's and Phobos's are left as the IAU has them,
and so are the circles Ariel's, Umbriel's, Titania's and Oberon's poles go round on, at rates none
of their nodes has), and Iapetus's pole follows its orbit normal
(`lockedToOrbit`), so each keeps its face to its planet from AD 1 to 3000; other
stars get their confirmed exoplanets. Orbits are drawn as ellipses and bodies are propagated
along them by a Kepler solver to the date on the map's clock. Under them, a dashed grid marks out
@@ -333,7 +337,7 @@ plugin's own files are kept so it can be listed from a marketplace of its own la
## Data credits
Star catalogue: [HYG database](https://github.com/astronexus/HYG-Database) (Hipparcos, Yale
Bright Star, Gliese) — 68 388 stars within 250 pc. Solar-system orbits: JPL approximate planetary mean elements (Standish), JPL SSD satellite mean elements and the JPL Small-Body Database; rotation: the IAU WGCCRE 2015 report via NAIF's pck00011, with a locked moon's W and node terms re-rated to its JPL mean elements and Iapetus's pole carried round its orbit normal, and for Earth the IERS Conventions 2010; physical data, and the positions the orbits are checked against: NASA/JPL Horizons. Exoplanets: NASA Exoplanet
Bright Star, Gliese) — 68 388 stars within 250 pc. Solar-system orbits: JPL approximate planetary mean elements (Standish), JPL SSD satellite mean elements and the JPL Small-Body Database; rotation: the IAU WGCCRE 2015 report via NAIF's pck00011, with a locked moon's W and its pole's terms within 5 per cent of its node's rate re-rated to its JPL mean elements (but the Moon's and Phobos's) and Iapetus's pole carried round its orbit normal, and for Earth the IERS Conventions 2010; physical data, and the positions the orbits are checked against: NASA/JPL Horizons. Exoplanets: NASA Exoplanet
Archive. Deep-sky objects: [OpenNGC](https://github.com/mattiaverga/OpenNGC). Body and skybox
imagery: NASA/JPL/USGS public domain and Solar System Scope (CC BY 4.0) — per-file provenance
is recorded in `src/assets/textures/README.md`.