moon_position_eci
Defined in: ephemeris.rs:40
fn moon_position_eci(epoch: &[Epoch<Tdb>](../../structs/epoch/)) -> [Vec3<frame::Gcrs>](../../structs/vec3/)
Moon position vector in ECI (J2000) frame [km].
Uses the analytical model from Meeus “Astronomical Algorithms” Chapter 47 with full periodic term tables (60 terms for longitude/distance, 60 for latitude), E correction factor, and planetary perturbation corrections.
Accuracy: ~10” in ecliptic longitude, ~1% in distance (~4,000 km).
The Meeus series is referred to the mean equinox and equator of date (its
mean longitude L' = 218.3164477 + 481267.88123421·T advances at the
tropical rate, and the ecliptic → equatorial rotation uses the mean obliquity
of date), so the result is rotated back to J2000 with the IAU 1976 precession
(crate::earth::fk5) before being typed Vec3<Gcrs>. Skipping that
rotation would be a secular 0.335° direction error in 2024 — ~2,250 km
transverse on the Moon vector, well above the model’s own ~10″ longitude
accuracy. Nutation (≤ 17″) and the J2000→GCRS frame bias (~20 mas) are
neglected.
Time scale
Section titled “Time scale”Meeus ephemerides take a dynamical time argument (TDB), so this signature
requires &Epoch<Tdb> — the caller converts at the boundary
(utc.to_tdb()). (The MoonEphemeris trait, which also abstracts a
UTC-indexed Horizons table, deliberately keeps a &Epoch<Utc> interface;
see MeeusMoonEphemeris.)