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When and why did the Jews switch to a perpetual calendar?

by Rabbi Naftali Silberberg


Library » Miscellaneous » The Jewish Calendar | Subscribe | What is RSS?


The Jewish calendar is supposed to be, and originally was, based on the ongoing proclamations of the Sanhedrin. (See How does the Jewish calendar work?) Only a Sanhedrin which was ordained in the Land of Israel was allowed to consecrate Rosh Chodesh or designate a Leap Year.

In the 4th century CE, the sage Hillel II foresaw that the Jews would be exiled from Israel, and be spread over the entire globe, therefore they would no longer be able to follow a Sanhedrin-based calendar. So Hillel and his rabbinical court established a perpetual calendar. They consecrated all the Rosh Chodeshim and leap years until Moshiach will come and reestablish the Sanhedrin.

See also What is the cycle of the Jewish calendar?


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Posted by: Samuel David Henderson, Colona, IL on Apr 13, 2006

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The Messiah. Moshiach is the person who will usher in an era of peace and tranquility for all of humanity when there will be no jealousy or hate, wars or famine. This is a fundamental Jewish belief.
Leap Year
Every 2-3 years an extra month is added to the Jewish calendar. Since the lunar year, which Jews follow, is 11 days shorter than the solar year, it is necessary to keep pace, so that holidays corresponding to certain seasons remain in sync. On a leap year, a second month of Adar is added.
The Jewish Supreme Court. The court would convene in a designated chamber in the Holy Temple, and was comprised of 71 of the greatest scholars of the time. Continued after the destruction of the Temples, but was dissolved in the 5th century when due to Roman persecution the seat of Torah scholarship relocated from Israel to Babylon.
Rosh Chodesh
The "Head of the Month," Rosh Chodesh is observed the first day of every Jewish month. If the previous month had 30 days, then the last day of the previous month is also observed; hence a two-day Rosh Chodesh. Rosh Chodesh is a semi-holiday, marked by Torah-reading and special prayers.