Show HN: Moon Phase Algorithms for C, Lua, Awk, JavaScript, etc.

Summary

moonphase - Werewolf Early Warning System A collection of snippets that get the phase of the moon, currently, the implementations are: Systems Level Languages: C/C++ Rust Zig Scripting Languages: Lua JavaScript Python DSLs: awk bc These functions take a time as an input (usually in unix epoch seconds or the languages official way of doing time), and return the "age" of the moon in radians, such that (1-cos(x))/2 returns the illuminated fraction of the moons surface, this indirection is needed because across a full cycle, the same illuminated percent appears more than once, the first and third quarter are a good example. All implementations contain test cases showing how to get the illuminated fraction and percent using the code. When the age of the moon is converted into a range between [0,1] . You can then get the age of the moon in days by multiplying it by ~29.5. You can also get the "index" of the phase, required for the phase name and emoji, with the illuminated fraction and the angle. As an example, here's some rust code for a different tool using the same algorithm: fn phaseidx ( ilumfrac : f64 , ang : time :: Angle ) -> usize { match ( ilumfrac , ang . degrees ( ) > 90.0 ) { ( 0.00 .. 0.04 , _ ) => 0 , ( 0.96 .. 1.00 , _ ) => 4 , ( 0.46 .. 0.54 , true ) => 6 , ( 0.46 .. 0.54 , false ) => 2 , ( 0.54 .. 0.96 , true ) => 5 , ( 0.54 .. 0.96 , false ) => 3 , ( _ , true ) => 7 , ( _ , false ) => 1 , } } (Note that your angle has to be converted to a positive angle with a-360.0*(floor(a/360)) or some similar modulo (not remainder) operation) All these snippets are based off the algorithm in moontool , a GUI program made in the 80s by John Walker, which based its algorithms off the book Practical Astronomy With Your Calculator. Rules for submission of [Favorite Language Here] These rules may be bent for microlanguages and DSLs. The Copy and Paste Rule