Links

A thorough history of the Julian and Gregorian calendars (and an interesting argument about when the new millennium actually began):

http://serendipity.magnet.ch/hermetic/cal_stud/cal_art.htm

Clear technical definitions of the two calendars are given here:

http://scienceworld.wolfram.com/astronomy/

See a comprehensive coverage of these and other calendars at

http://astro.nmsu.edu/~lhuber/leaphist.html

Readings

Heritage Mathematics, Cameron, M. (Hargreen, 1983)

Makers of Mathematics, Hooper C. (Faber, 1961)

History of Mathematics, Smith, D.E. (Dover, 1958)

A Sourcebook of School Mathematics, (NCTM, 1980)