BPAA Lecture Series 2003
Astronomies and Rituals at the Dawn of the Middle Ages, Stephen C. McCluskey in Astronomies and Cultures, Clive Ruggles editor, University of Colorado Press, 1993
Astronomy Before the Telescope, Edited by Christopher Walker, St. Martins, New York, 1996.
This is a good general reference on the early history of astronomy with articles by well respected specialists.
Calendrical Calculations, Nachum Dershowitz and Edward Reingold, Cambridge 1997.
This book provides everything you ever wanted to know about calendar conversion. Calendars include the Julian, Gregorian, Hebrew, Hindu, Chinese and Mayan.
Calendar, Humanity's Epic Struggle to Determine a True and Accurate Year, David, E. Duncan, Avon, 1998.
This is a very readable and reliable account of the development of the calendar in western civilization.
Marking Time, Duncan Steel, Wiley, 2000
A somewhat rambling but very interesting account of the history of the calendar.
Hamlet's Mill, Giorgio deSantillana and Hertha von Dechend, Gambit, Boston, 1969.
An important, challenging and under appreciated book about the connection between the precession of the equinoxes and ancient myths around the world.
Easter link2 provides some colorful background and lots of details about the determination of Easter.