CALENDAR

The Jewish year was composed of twelve lunar months (beginning on the day of the new moon), with an inter-calary month added periodically. In some traditions, and perhaps originally, the year began in the fall, at the autumnal equinox (see Ex 23.16; 34.22). In others, following Babylonian practice, the new year was celebrated in the spring. The fall new year, commencing with Rosh Ha-Shanah, became standard in postbiblical Judaism.

Months in the Bible are usually identified by ordinal numbers, beginning with the spring new year. Some months (in boldface in the following list) are also designated with names derived either from a Canaanite calendar or, in postexilic texts, from a Babylonian one; the names of months not found in the Bible are known from other ancient sources.

The Jewish calendar is based on the lunar month, which is a bit longer than 291/2 days, so Jewish lunar months are 29 or 30 days long. Twelve lunar months usually amount to 354 days, 11 days short of a solar year. In order for the festivals to stay in the correct season in relation to the solar year, an extra month is added every few years. Following ancient Babylonian models, the calendar runs on a 19-year cycle: years 3, 6, 8, 11, 14, 17, and 19 of the cycle are intercalated or “leap” years, containing an extra month of Adar, sometimes called Adar Sheni (second Adar). Adar was chosen for intercalation because it is the last month of the Babylonian year and of the biblical year beginning in Nisan (as noted above, an alternate calendar, now in use, begins the year in Tishri with Rosh Ha-Shanah.) The previous 19-year intercalation cycle began in 5768 (2007–2008 ce).

Observances fall within the calendar as follows: