The Explanatory Supplement to the Astronomical Almanac offers explanatory material, supplemental information and detailed descriptions of the computational models and algorithms used to produce The Astronomical Almanac, which is an annual publication prepared jointly by the US Naval Observatory and Her Majesty\"s Nautical Almanac Office in the UK....

The Explanatory Supplement provides a detailed description of how to perform practical astronomy or spherical astronomy. This completely revised and rewritten edition is an authoritative source on astronomical phenomena and calendars....