The Jewish Calendar

For those people who don't understand why Jewish holidays fall on different dates (sometimes even different months), I thought I'd discuss the Jewish Calendar so as to demystify the celebration process.

The Jewish Calendar is Based on a Lunar Model Which Adjusts for the Solar Year

Unlike the secular calendar, the Jewish Calendar is based on the Moon. But, unlike the Muslim calendar, the Jewish calendar adjusts to fit the solar year. This is why holidays fall on different dates, but generally fall during the same time of year, for instance, Passover is also called Hag Ha'Aviv, the Holiday of Spring.

The Jewish calendar is composed of 12 months. These months (starting, generally around September) are:

1) Tishrei

2) Heshvan

3) Kislev

4) Tevet

5) Shevat

6) Adar

7) Nissan

8) Iyar

9) Sivan

10) Tammuz

11) Av

12) Elul

(You can find out more information about a specific month by clicking on the names of the months that are links)

Nissan, which is the month of spring and the month of Passover, is considered the first month in the Tora (the 5 books of Moses -- the first 5 books of the Hebrew Bible) because it is the month that the Children of Israel became a nation.

In order to keep the Jewish calendar from falling behind the solar year, the Jewish calendar provides for 7 leap years (called "Shana M'uberet" or, literally, a pregnant year) every 19 years. The Jewish leap year includes not one leap day (like February 29th on the secular calendar) but an entire leap month. This month is called Adar Sheini or Adar II. Adar II comes after Adar I (making them months 12 and 12a, so to speak).

Because of this 19 year cycle, people who keep track of both secular and religious birthdays often have the dates fall together every 19 years.

On the Jewish calendar, every month has either 29 or 30 days. This is because the cycle of the moon around the earth is 29 1/2 days. In ancient times, witnesses would testify that they saw the new moon and the Jewish court would declare the new month (or Rosh Hodesh -- literally the Head of the Month). But in modern times, the calendar is planned in advance to ensure that certain holidays don't fall on certain days of the week (for example, Yom Kippur cannot fall on Sunday or Friday because observance of the Shabbat, the Sabbath, requires a "25 hour day" and the observance of Yom Kippur also requires a "25 hour day" -- and you can't have two "25 hour days" in a row).

Most months always have either 29 or 30 days every year, but certain months can have either, depending on the year. Kislev, the month during which Hanuka falls, is one such month and, because of this, the date that Hanuka ends is not always the same -- it can end on either the 2nd or 3rd of Tevet.

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