30. What is the calendar like that the Jewish people use?

The Jewish Calendar

“When is Hanukkah this year?”  “When is Passover this year?”  Jewish holidays do not change from year to year. Holidays are celebrated on the same day of the Jewish calendar every year, but the Jewish year is not the same length as a year on the Gregorian (solar) calendar used by most of the western world, so the date shifts on the Gregorian calendar.

Background and History

The Jewish calendar is primarily lunar, with each month beginning on the new moon, when the first sliver of moon becomes visible after the dark of the moon. In ancient times, the new months used to be determined by observation. When people observed the new moon, they would notify the Sanhedrin. When the Sanhedrin heard testimony from two independent, reliable eyewitnesses that the new moon occurred on a certain date, they would declare the rosh chodesh (first of the month) and send out messengers to tell people when the month began.

The problem with strictly lunar calendars is that there are approximately 12.4 lunar months in every solar year, so a 12-month lunar calendar loses about 11 days every year and a 13-month lunar gains about 19 days every year. The months on such a calendar “drift” relative to the solar year.

Numbering of Jewish Years

The year number on the Jewish calendar represents the number of years since creation, calculated by adding up the ages of people in the Bible back to the time of creation.

Jewish people do not generally use the words “A.D.” and “B.C.” to refer to the years on the Gregorian calendar. “A.D.” means “the year of our Lord.”  Instead, they use the abbreviations C.E. (Common or Christian Era) and B.C.E. (Before the Common Era).

Months of the Jewish Year

The “first month” of the Jewish calendar is the month of Nissan, in the spring, when Passover occurs. However, the Jewish New Year is in Tishri, the seventh month, and that is when the year number is increased. This concept of different starting points for a year is not as strange as it might seem at first glance. The American “new year” starts in January, but the new “school year” starts in September, and many businesses have “fiscal years” that start at various times of the year. Similarly, the Jewish calendar has different starting points for different purposes.

The names of the months of the Jewish calendar were adopted during the time of Ezra, after the return from the Babylonian exile. The names are actually Babylonian month names, brought back to Israel by the returning exiles. Note that most of the Bible refers to months by number, not by name.

Name	Number	Length	Gregorian Equivalent
Nissan	1	30 days	March-April
Iyar	2	29 days	April-May
Sivan	3	30 days	May-June
Tammuz	4	29 days	June-July
Av	5	30 days	July-August
Elul	6	29 days	August-September
Tishri	7	30 days	September-October
Cheshvan	8	29 or 30 days	October-November
Kislev	9	30 or 29 days	November-December
Tevet	10	29 days	December-January
Shevat	11	30 days	January-February
Adar	12	29 or 30 days	February-March
Adar  II	13	29 days	March-April