The subsolar point and colongitude #9

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opened 2026-10-22 22:33:50 -05:00 by jeff · 0 comments

jeff commented

2026-10-22 22:33:50 -05:00

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Part of #1

Parent

What to build

The subsolar point in selenographic coordinates and the colongitude at an instant, from ch. 53, using the same sign convention as libration so that the two can be combined on one map.

The subsolar longitude is reported in (−180°, +180°] and the colongitude in [0°, 360°).

Acceptance criteria

Ch. 53's worked example for the selenographic position of the Sun passes to the printed precision
The subsolar point is added to the Horizons reference tables and agrees within the stated tolerance
Property: colongitude is 90° minus the subsolar longitude, modulo 360°
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 The **subsolar point** in **selenographic coordinates** and the **colongitude** at an **instant**, from ch. 53, using the same sign convention as libration so that the two can be combined on one map. The subsolar longitude is reported in (−180°, +180°] and the colongitude in [0°, 360°). ## Acceptance criteria - [ ] Ch. 53's worked example for the selenographic position of the Sun passes to the printed precision - [ ] The subsolar point is added to the Horizons reference tables and agrees within the stated tolerance - [ ] Property: colongitude is 90° minus the subsolar longitude, modulo 360° - [ ] 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 22:33:50 -05:00

jeff added a new dependency

2026-10-22 22:33:53 -05:00

#4 The Sun's apparent position

jeff added a new dependency

2026-10-22 22:33:53 -05:00

#8 Libration and the position angle of the axis

jeff self-assigned this

2026-10-23 00:17:05 -05:00