Astronomy · Reference chapter
Calendars
E. G. Richards
A technical account of calendar systems, their history and conversion algorithms. This chapter distinguishes astronomical cycles from arithmetic and religious calendars.
Open the source PDF ↗Where to begin
Section 15.1 for calendar types; 15.4 for Gregorian Easter; 15.6 for the Islamic calendar; 15.11 for conversion algorithms.
Keep in mind
This is one chapter, not the complete book. An arithmetic date is not a crescent-sighting announcement, and an ecclesiastical full moon is not a calculated astronomical full moon. The PDF is linked at its authorized host.