NISAN

(Niʹsan).

The postexilic name of the first Jewish lunar month of the sacred calendar, corresponding to part of March and part of April. (Ne 2:1; Es 3:7) This month, first called “Abib,” was originally considered the seventh month and is evidently the month referred to at Genesis 8:4. At the time of the Exodus from Egypt, Jehovah assigned this month to be “the first of the months of the year.” (Ex 12:2; 13:4; Nu 33:3) From then on, a distinction existed between a sacred calendar instituted by Jehovah and the previous secular calendar.​—See CALENDAR; ABIB.

Adjusting the Lunar Calendar. God’s command required that the Israelites offer up a sheaf of the firstfruits of their harvest on the 16th day of Nisan (Abib) and that, on the 50th day thereafter, they offer up a second grain offering. These offerings corresponded naturally with the barley and wheat harvests, respectively. This precept made essential an adjustment in the calendar of lunar months used by the Israelites. There was need to compensate for the difference of 11 1⁄4 days between the full solar year and the shorter lunar year. Otherwise, within the space of three years, the month of Nisan would arrive some 33 days earlier in the season and far ahead of the barley harvest. The Bible record does not specify what method was originally used by the Israelites to accomplish such coordination, but the evidence indicates that a 13th month was added every two or three years to restore the seasons to their proper position in the calendar year. It seems likely that this was determined by simple observation, relating the new moon to the vernal, or spring, equinox of the sun, which comes about March 21 of each year. If the new moon that would ordinarily mark the start of the month of Nisan (Abib) was too distant from the time of the spring equinox, then the month was counted as a 13th or intercalary month, and Nisan began with the following new moon. It was not until the fourth century C.E. that a definitely standardized calendar was adopted by the Jews.