The Jewish Calendar
©2009 By David Talbot
Here’s something people ask me all the time: “Why do Jewish Holidays fall on different days each year?” There is a simple answer. But, like most things Jewish, I am going to make it more complicated.
The simple answer is that the Jewish calendar is based on the cycles of the moon (A lunar calendar). The Gregorian calendar is based on the cycles of the Sun (A solar calendar). Now we, here and around the world that rely on the Gregorian solar calendar, know the earth revolves around the sun every 365.25 days a year. That pesky little extra causes us to add one day to February, every four years. Why February? My guess is that in Roman times, February was the last month of the year. So it was convenient to add it at the end of February.
But the lunar calendar is totally different. The lunar cycle is about 29.5 days. And the Jewish Calendar has 12 months with 12 lunar cycles resulting in a Jewish year having 355 days. Some months have 29 days and some have 30. So, every 3 years, in stead of adding a day, Jewish calendars add an entire month, the month of Adar (more or less around February).
The Muslim calendar is also based on lunar cycles. But their approach is to simply come to the end of the year and start over, not adding days or months. The result is that any particular Muslim holiday, such as Ramadan, may occur in Winter, Spring, Fall or Summer.
So, the question is, why does the Jewish calendar require periodic resetting? The answer is in the nature of the Jewish Holidays through out the year. Many Jewish holidays are linked to agricultural events, like the planting or harvesting of crops. So these festivals need to be at specific times in the agricultural cycle. As a result, unlike the Muslim calendar, the Jewish calendar must be re-set so that Passover always occurs in the Spring and Succoth in the Fall.
The fact that Jewish holidays do not always fall on the same dates on the Gregorian calendar is simply a matter of the difference in the number of solar days vs. the number of lunar days in the respective calendars.
Of course, I always answer the question (“Why do Jewish Holidays fall on different days each year?”) with the following example: Chanukah always falls on the same day every year, the 25th of Kislev, on my calendar.