Understanding the Explanatory Supplement to the Astronomical Almanac
The IAU’s Standards of Fundamental Astronomy (SOFA) initiative provides free, officially sanctioned software routines (in C and Fortran) that implement the algorithms explained in the supplement.
: The specific formulas and algorithms used for orbital ephemerides and coordinate transformations. Evolution of the Editions Publication Year Primary Changes First
An IAU initiative that provides officially endorsed software routines (in C and Fortran) implementing the algorithms described in the supplement. The accompanying PDF manuals for SOFA libraries act as a free, highly technical software supplement.
Detailed models explaining the wobbles in Earth’s rotational axis and how to calculate their effects over time.