Fun with the Hebrew Calendar

CalendarThere is a Jewish joke that says: Two Jews are in a synagogue, and one turns to the other as asks “when is Hannukah this year?” and the other responds “the same as always, on the 25th of Kislev.” This little tale helps us to learn about the Hebrew calendar. Jewish holidays are celebrated on the same day of the Hebrew calendar each year, but since the Hebrew year is not the same as the solar year used by most of the Western world, Jewish holidays always fall on a different Western calendar day each year.

This quirky calendar difference can be confusing. My husband likes to celebrate birthdays and anniversaries using the Hebrew date and this takes some effort on my part to keep track. I am fortunate that the two most important dates I need to remember happen to fall on important dates in both calendars. In the year that my husband was born, the first night of Hanukkah fell on December 25—Christmas Day—and that day is his birthday. Every year, we celebrate the first night of Hanukkah and Nathan’s birthday. Last year, it was also Thanksgiving, which made it a triple celebration! We got married on the 18th of the Hebrew month of Lyar, which is also the Jewish holiday of Lag B’Omer, another special day that is on every Jewish calendar, making it easy to remember our anniversary.

The Hebrew calendar has a fascinating twist, a method to reconcile the lunar and solar years. The secular calendar is based on the solar cycle, in which the earth revolves around the sun in approximately 365¼ days. Since we cannot measure a quarter of a day, we have 365 days each year, and every 4th year add a 366th day, creating a leap year every four years. The Jewish calendar consists of months based on the lunar cycle, the time it takes the moon to revolve around the earth. A lunar month consists of 29½ days. Again, since we cannot have ½ day, we have some Hebrew calendar months with 29 days, and some with 30 days. As a result of the extra half days, the Hebrew calendar also includes some leap years.

Every so often, 7 times out of every 19 years, the Jewish calendar adds an extra month of Adar and names them Adar I and Adar II. This year, 2014/5774 has one of those fun occurrences. The reason for the extra Adar is that a solar year consists of 365 days, and a lunar year consists of 354 days, causing the same Hebrew calendar day to occur 11 days earlier in the following year. As a result, Passover which is supposed to occur in springtime, would happen earlier and earlier each year, eventually ending up in the winter, fall, and summer. To prevent this backward slippage, the Jewish sages added an extra month to reconcile the Jewish and secular calendars.

This leap month is called Adar Sheni, or Adar the 2nd (Adar II). Interestingly, Adar II is the month that is constant every year, where Adar I, is the one added in a Hebrew leap year. The way we know this is that Purim, which always occurs in the month of Adar, is celebrated during Adar II in a leap year. Interestingly, a year consisting of 13 months is not called a leap year, but Shana Me’uberet, a pregnant year.

During Talmudic times, the Hebrew calendar was established by the Rabbinic court in Jerusalem, based upon the sighting of the new moon by two witnesses, who were quizzed to determine the reliability of their testimony. In the 4th Century, the Jewish sage Hillel II, established a fixed calendar, basing it on mathematical and astronomical calculations. This is the Hebrew calendar that we use today to know precisely when to celebrate holidays in the current year, and to help us plan for the future.

It is a fun activity to compare the Hebrew and Western calendars to find out if you were born or married on a Jewish holiday, important day in Jewish history, or if you share a birthday with a famous Jewish leader or prophet. You can find a Hebrew date using the online HebCal date converter and then see what happened on that Day in Jewish History. I was born on the 30th day of the month of Sivan, which is a day of celebrating the new moon and the day before Joseph, the Son of Jacob and Rachel was born!