The Sun's apparent position #4

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opened 2026-10-22 22:33:47 -05:00 by jeff · 0 comments

jeff commented

2026-10-22 22:33:47 -05:00

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Part of #1

Parent

What to build

astro.sun.position: the Sun's apparent position at an instant — ecliptic longitude and latitude, distance_au, right ascension and declination — from ch. 25's low-accuracy algorithm (about 0.01°, which the documentation states).

This ticket also sets up the JPL Horizons reference tables the rest of the work compares against: a data file checked into the repository together with the exact Horizons query that produced it, and a test that compares public results to it with a tolerance stated beside each quantity. It is seeded with the Sun's apparent position at sample instants spanning 1900–2100.

Acceptance criteria

Ch. 25's worked example passes to the printed precision
The Sun's position agrees with Horizons across 1900–2100 within the stated tolerance
The Horizons query is recorded so the data can be regenerated
Properties: every finite result is in its documented range; NaN or ±∞ in gives NaN out
Every new public declaration has a doc comment giving units, time scale and reference frame, and citing the chapter and equation of Meeus it implements
Every source used is in the README's references cited
zig build test, zig build check, zig fmt --exclude zig-pkg --check . and reuse lint pass

Part of #1 ## Parent #1 ## What to build `astro.sun.position`: the Sun's **apparent position** at an **instant** — ecliptic longitude and latitude, `distance_au`, right ascension and declination — from ch. 25's low-accuracy algorithm (about 0.01°, which the documentation states). This ticket also sets up the JPL Horizons reference tables the rest of the work compares against: a data file checked into the repository together with the exact Horizons query that produced it, and a test that compares public results to it with a tolerance stated beside each quantity. It is seeded with the Sun's apparent position at sample instants spanning 1900–2100. ## Acceptance criteria - [ ] Ch. 25's worked example passes to the printed precision - [ ] The Sun's position agrees with Horizons across 1900–2100 within the stated tolerance - [ ] The Horizons query is recorded so the data can be regenerated - [ ] Properties: every finite result is in its documented range; NaN or ±∞ in gives NaN out - [ ] Every new public declaration has a doc comment giving units, time scale and reference frame, and citing the chapter and equation of Meeus it implements - [ ] Every source used is in the README's references cited - [ ] `zig build test`, `zig build check`, `zig fmt --exclude zig-pkg --check .` and `reuse lint` pass

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2026-10-22 22:33:47 -05:00

jeff added a new dependency

2026-10-22 22:33:51 -05:00

#3 Angles, coordinates, nutation and obliquity

jeff added a new dependency

2026-10-22 22:33:51 -05:00

#5 The Moon's apparent position

jeff added a new dependency

2026-10-22 22:33:52 -05:00