THE JEWISH CALENDAR

Rabbi Rifat Sonsino, Ph.D

It is not clear which calendar the biblical Israelites followed, whether lunar or solar. Gen, 1:14 tells us:  “ God said: let there be lights in the expense of the sky to separate day from night; they shall serve as signs for the set times-the days and the years.”  The reference here is to the moon and the sun that had been created by God. The are not to be worshipped as deities. 

Yehudah ha-Parsi (“Judah, the Persian”), a 9^th century rabbinic scholar, argued that the biblical calendar was solar, whereas Ibn Ezra, a 12^th cent. rabbinic commentator, maintained that it was lunar, but even he had to acknowledge that his opinion was based on oral tradition.

On the other hand, the Book of Jubilee (2^nd cent. BCE) upheld a sectarian calendar of 364 days, one day less than the solar calendar, and 10 days longer than the lunar calendar. The Dead Sea Scrolls followed this system, which showed that during the second temple period, their calendar deviated from the biblical priestly calendar found in the Pentateuch and observed in Jerusalem. It may be one of the reasons why the Dead Sea community (the Essenes???) abandoned Jerusalem in protest and moved to their location in the desert. 

Around the year 175 BCE, for tax purposes, the Romans imposed their own lunar calendar on the Jewish community in Israel by removing the high priest Onias the 3^rd, who refused to accept the change, and appointed Jason his brother, who accepted it.

Today, the Jewish (rabbinic) calendar is based on the Babylonian practice and it is a combination of the lunar and solar systems. Even the names of the months are of Babylonian origin. Thus, for example, the first Hebrew month, Nisan is named after the Babylonian month, nisannu; the last month, Adar is named after the Babylonian month, adaru. 

The solar year is 365 days long, whereas the lunar year is 

354 days long, with a difference of about 11 days between the two. So, in order to make up this difference, a leap year is declared every few years. 

In this system, the calculation of the months begins in the springtime following the movement of the moon -thus, Passover is always in the spring, and the years are counted from the fall on- thus Rosh Hashanah, the New year, always falls in the fall. 

It is this combined system that determines all the Jewish holidays every year today.