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).
