Trouble computing moon phases

[westy92]

Hi 👋

I'm trying to calculate the various moon phases during a particular lunation number. However, the results don't make sense. 😕

let lunation_num = moon_phase::get_lunation_number(1735711200); // result: 309. 1 Jan 2025 00:00:00 -0600 
let new_moon = moon_phase::get_new_moon(lunation_num);          // 1735597609, 30 Dec 2024 16:26:49 -0600
let first_q = moon_phase::get_first_quarter_moon(lunation_num); // 1735617118, 30 Dec 2024 21:51:58 -0600
let full_moon = moon_phase::get_full_moon(lunation_num);        // 1735597522, 30 Dec 2024 16:25:22 -0600
let last_q = moon_phase::get_last_quarter_moon(lunation_num);   // 1735616667, 30 Dec 2024 21:44:27 -0600

I expected each phase to be at least a few days apart, but instead, they are a few hours apart. Am I doing something wrong here, or is this a bug?

[vinc]

Hi Seth! It's not really a bug but the way to use those four functions is really ugly and lead easily to this issue..

If you look here: https://github.com/vinc/geodate/blob/master/src/ephemeris.rs#L31

It seems that you need to do this:

let lunation_num = moon_phase::get_lunation_number(1735711200);
let new_moon = moon_phase::get_new_moon(lunation_num);
let first_q = moon_phase::get_first_quarter_moon(lunation_num + 0.25);
let full_moon = moon_phase::get_full_moon(lunation_num + 0.50);
let last_q = moon_phase::get_last_quarter_moon(lunation_num + 0.75);

I have a patch somewhere to change the signature of those functions to use an integer for the lunation number instead of a float and hide this complexity inside them when calling get_time_of(phase: MoonPhase, lunation_number: f64).

[westy92]

@vinc thank you for the quick response! Adding those values seems to solve it.