It uses the Python lib Astral, which uses "equations from Astronomical Algorithms, by Jean Meeus", to find location of the Sun in the sky. That method assuming earth motion without gravitational pull from other planets or the Moon, and has accuracy of 0.01 arc degree. Meeus is a rock star in these kinds of calculations. He also gave a truncted version of VSOP87 that has error less than 1 arc second in finding Sun's location.
The method Astral uses for calculate Moon's location has precision of 1 arc minute. For higher precision, LEA-406 [1] can be used.
The method Astral uses for calculate Moon's location has precision of 1 arc minute. For higher precision, LEA-406 [1] can be used.
[1] https://www.aanda.org/articles/aa/full/2007/33/aa7568-07/aa7...