The New Unger's Bible Dictionary
CALENDAR
(Lat. calendarium, from calere, "to call," because the priests called the people to notice that it was new moon). An ecclesiastical almanac indicating the special days and seasons to be observed�
Jewish. The Israelites divided their year according to natural phenomena exclusively, combining the solar and lunar year. The months began with the new moon, but the first month was fixed (after the Exodus and by the necessities of the Passover) by the ripening of the earliest grain, namely, barley. The lunar month averaging 29 1/2 days, a year of twelve months of 30 and 29 days alternately resulted; but this involved a variation of 11 and 22 days alternately in eighteen out of nineteen years. To reconcile this lunar year with the year of the seasons, a thirteenth month was inserted about once in three years. That the Jews had calendars wherein were noted all the feasts, fasts, and days on which they celebrated any great event of their history is evident from Zech 8:19. Probably the oldest calendar is the Megillath Taanith ("volume of affliction"), said to have been drawn up in the time of John Hyrcanus, before 106 BC See Chronology.
(from The New Unger's Bible Dictionary. Originally published by Moody Press of Chicago, Illinois. Copyright (c) 1988.)
The Jewish Calendar in Ancient Hebrew History
