Crate stem_branch 

Native Rust port of stem-branch’s solar ephemeris core.

Computes the Sun’s geocentric ecliptic state from the full VSOP87D Earth series plus a JPL DE441-fitted correction polynomial and IAU2000B nutation. Input is a Julian Ephemeris Day in Terrestrial Time (JDE/TT); the UTC<->TT / ΔT boundary is the caller’s responsibility.

This is a faithful translation of the TypeScript solarEclipticState; the VSOP87D and IAU2000B coefficient tables are generated from the same source by scripts/gen-rust-solar-data.mjs.

Structs

CivilDate

A Gregorian civil date in Beijing time.

LunarMonth

One month of a lunisolar year: its number, leap flag, Gregorian start date (正月初一 etc., Beijing), and length in days (29 or 30).

LunisolarDate

A Chinese lunisolar date.

MoonPhase

Illumination geometry of the Moon at a Julian Ephemeris Day (TT), from the Moon’s and Sun’s geocentric positions (ELP/MPP02 + VSOP87D). Computed per Meeus, Astronomical Algorithms 2e, chapter 48 — using the true geocentric elongation (including the Moon’s ecliptic latitude) and the Sun/Moon distances, not a longitude-only approximation.

MoonState

Apparent geocentric position of the Moon at a Julian Ephemeris Day (TT): ELP/MPP02 geometric place, precessed to the ecliptic of date and corrected for nutation in longitude, then resolved to equatorial coordinates.

SolarState

Geocentric solar ecliptic state at a Julian Ephemeris Day (TT).

Constants

EARTHLY_BRANCHES

The twelve Earthly Branches (地支), index 0 = 子.

HEAVENLY_STEMS

The ten Heavenly Stems (天干), index 0 = 甲.

SOLAR_TERM_LONGITUDES

Apparent ecliptic longitude (degrees) for each term; index 0 = 小寒 at 285°.

SOLAR_TERM_NAMES

Traditional-Chinese names of the 24 solar terms, index-aligned with SOLAR_TERM_LONGITUDES (index 0 = 小寒 @ 285°). Ported verbatim from the TypeScript SOLAR_TERM_NAMES (src/solar-terms.ts).

Functions

delta_t_for_year

ΔT in seconds for a decimal year (TT = UT + ΔT).

find_new_moons_in_range

All new-moon JDEs (TT) within the Julian-Day range [start_jd, end_jd].

find_solar_term_moment

Find the JD(UT) of the solar term at target_longitude in year, searching from the first of start_month. Returns None if not found in 120 days.

gregorian_to_lunisolar

Convert a Gregorian (Beijing) civil date to its Chinese lunisolar date.

gregorian_to_lunisolar_with

As gregorian_to_lunisolar, with a caller-supplied ΔT model (decimal year → seconds) — e.g. to match an authority’s calendar at a ΔT-uncertain far-future boundary. Bypasses the per-year cache.

jd_from_ymd

Julian Day at 00:00 UT of the given Gregorian calendar date.

lunar_months_for_year

Lunar months for the lunisolar year whose 正月 falls in lunar_year — 12 months, or 13 in a leap year.

lunar_new_year

The Lunar New Year (正月初一) Gregorian date for gregorian_year.

moon_phase

Compute the Moon’s phase geometry (elongation, phase angle, illuminated fraction) at the given Julian Ephemeris Day in Terrestrial Time.

moon_position

Compute the Moon’s apparent geocentric position at the given Julian Ephemeris Day in Terrestrial Time.

new_moon_jde

JDE (TT) of the true new moon (定朔) for integer lunation k: the Meeus Ch.49 estimate refined to the exact Sun–Moon apparent-longitude conjunction using the ELP/MPP02 Moon and VSOP87D + DE441 Sun. Sub-arcsecond — far tighter than Meeus alone (~1 minute), which is what fixes the rare near-midnight calendar boundary where a coarser instant could land on the wrong day.

solar_ecliptic_state

Compute the Sun’s geocentric ecliptic state at the given Julian Ephemeris Day in Terrestrial Time.

solar_term_for_longitude

The solar term in effect at apparent ecliptic longitude deg — the term whose longitude is the greatest one at or before deg (circular). Terms sit every 15° starting from SOLAR_TERM_LONGITUDES[0] (小寒, 285°). Inputs are normalized, so negative or >360 longitudes are accepted.

ymd_from_jd

Gregorian (year, month, day) of the civil day that contains instant jd, using the midnight (.5) day boundary.