Calendars in Old Testament Times

The calendar was important in the ancient world for regulating agricultural, religious, and legal activities. A version of the lunar calendar was commonly used throughout the ancient Near East. This “lunisolar” calendar was integral to Israelite culture and is reflected in the writings of the ot.

The New Year usually occurred in the spring, at the beginning of the growing season, with the month of Nisan (March/April). The Passover occurred in the first month, so its commemoration was linked to the observance of the beginning of the year (Exod 12:2). The Feast of Trumpets, which occurred during the seventh month, or Tishri (September/October; see Lev 23:23–25), was called Rosh Hashanah or the “head of the year”; it marked the end of the agricultural year (compare Exod 34:22).

The beginning of the month was reckoned by the first visible crescent of the new moon. The lunar month was 29 to 30 days long, and 12 lunar months added up to a 354-day lunar year. Because of variations on when the new moon might first become visible in different places, the rabbinic work the Mishnah established that the observance of the new moon in the Palestine region would be the official start of the month.

Both the ot and nt use lunar months for the dates of events, but sometimes different names appear for the months in the Bible. The Babylonian names appear most commonly, which seem to have been adopted after the exile (post 538 bc). Canaanite names appear for four of the months in pre-exilic contexts (see Exod 13:4; 1 Kgs 6:1; 6:38; 8:2).

Jewish literature from the Second Temple period indicates that a wide variety of sectarian groups followed both the traditional lunisolar calendar and a 364-day solar calendar. The usage of the solar calendar is attested to primarily in the book of Jubilees and the Dead Sea Scrolls. The use of both led to Sabbath and holiday observances on different days. The lunar cycle and the solar cycle were annually out of sync by about 11 days, so the lunisolar calendar was corrected periodically to realign the lunar months with the seasons. The most common method of reconciling the calendars was adding an extra month when necessary (called “intercalation”) which kept the months and seasons aligned. Intercalation was most often made by royal decree in Mesopotamia until around 500 bc. During the Persian period, a mathematical formula was developed for intercalation based on the correspondence between 19 solar years and 235 lunar months. Seven months were intercalated for every 19-year period.

Douglas Mangum

Further Reading

Israelite Calendar Table

Calendar CLBD

Feasts and Festivals of Israel CLBD