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>
