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The Jewish calendar is based on both the lunar and the solar cycles and is used for computing Jewish holidays. Hebrew
days begin at sunset when three stars are visible. An ordinary year has 12 months, and a leap year has 13
months. Every month starts approximately on the day of a new moon. There are three year lengths for ordinary years and
three for leap years.
| Year type |
Ordinary Year |
Leap Year |
| deficient |
353 |
383 |
| regular |
354 |
384 |
| complete |
355 |
385 |
In a regular year, months alternate between 29 and 30 days.
The Jewish New Year starts on 1 Tishri, called Rosh Hashana, which celebrates the creation of the world (assumed
to be 3761 BC). There is a rather complicated set of 5 rules for determining the date of Rosh Hashana. A formula for
computing Rosh Hashana is given by Berlekamp et al. (1982), and a Lisp program for computing the Jewish calendar by
Reingold and Dershowitz (1989).
 Calendar
Berlekamp, E. R.; Conway, J. H.; and Guy, R. K.
Winning Ways, For Your Mathematical Plays, Vol. 2: Games in Particular. London: Academic Press, p. 800, 1982.
Dershowitz, N. and Reingold, E. M. Calendrical Calculations: The Millennium Edition. Cambridge, England: Cambridge University Press, 1999.
Reingold, E. M. and Dershowitz, N. "Calendrical Calculations." Technical Report UIUCCDCS-R-89-1541.
Department of Computer Science, Univ. Illinois, Urbana-Champaign, IL, 1989. ftp://a.cs.uiuc.edu/.
Ross, K. L. "The Jewish and Moslem Calendars and the Era of Nabonassar." http://www.friesian.com/calendar.htm#nabo.
Ross, K. L. "The Jewish Calendar." http://www.friesian.com/calendar.htm#jewish.
Tøndering, C. "Frequently Asked Questions about Calendars." http://www.tondering.dk/claus/calendar.html.
Vardi, I. Computational Recreations in Mathematica. Redwood, CA: Addison-Wesley, p. 240, 1991.
© 1996-2007 Eric W. Weisstein
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