ChristianAnswers.Net WebBible Encyclopedia
Among the Egyptians the month of thirty days each was in use long before the time of the Exodus, and formed the basis of their calculations. From the time of the institution of the Mosaic law the month among the Jews was lunar. The cycle of religious feasts depended on the moon. The commencement of a month was determined by the observation of the new moon. The number of months in the year was usually twelve (1 Kings 4:7; 1 Chronicles 27:1-15); but every third year an additional month (ve-Adar) was inserted, so as to make the months coincide with the seasons.