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The Longest Year: The Secrets of the Jewish Calendar

Rabbi Yirmiyahu Kaganoff

When there was a Sanhedrin, months and years were calculated solely on the testimony of witnesses. How did we make the change to the fixed calendar, and how can we calculate our own calendar? Why does 5771 have 385 days, the most possible in any year? Answers to these questions, and some classified information, in this fascinating look at the Jewish calendar.

Wednesday, November 03, 2010

“Thirty days hath September / April, June, and November.”

If we were to adapt this poem to — l’havdil — our current, standardized Jewish calendar, we would say that thirty days hath Tishrei, Shvat, Nissan, Sivan, Av, and sometimes Cheshvan and Kislev.

But the idea of having a standardized Jewish calendar seems to counter a mishnah in Rosh HaShanah. That mishnah states that whether a specific month has 29 days or 30 days depends on whether witnesses saw the new moon and testified in beis din early enough to declare the 30th day Rosh Chodesh (i.e., the first day of the next month). In addition, the Gemara states that when necessary, Elul could be made 30 days long — which cannot happen in our calendar.

How did our empirical calendar become so rigid and predictable in advance?

The Torah (Shemos 12:2) commands the main beis din of the Jewish people (also known as the Sanhedrin), or a beis din specially appointed by them, to declare Rosh Chodesh upon accepting the testimony of witnesses who observed the new moon. The purpose of having eyewitnesses was not to notify the beis din that the moon had appeared; the beis din had extensive knowledge of astronomy and could predict exactly when and where the new moon would appear and what size and shape it would be.

Nonetheless, the Torah obligated the beis din to wait for witnesses, and they could only rule on whether the 30th day would be the last day of the old month or would become the first day of a new month, based on testimony. If no witnesses to the new moon arrived on the 30th day, then the 31st day became Rosh Chodesh, regardless of the astronomic calculations (Mishnah Rosh HaShanah 24a). At that point in Jewish history, then, any month could be either 29 or 30 days.

The Torah also commands us that Pesach must always fall during the spring (Devarim 16:1). This seemingly innocuous mitzvah actually requires considerable manipulation of the calendar, since months, derived from the word moon, are determined by the length of time from one new moon to the next, which is a bit more than 29½ days. A lunar year is, therefore, almost exactly 354 days.

The seasons of the year, on the other hand, are calculated according to the solar year, because seasons change based on the relative distance between the Earth and the sun. A solar year is a bit less than 365¼ days. Since Pesach must always take place during the spring, the calendar cannot be twelve lunar months every year, because over time the eleven-day discrepancy between the lunar and solar years would cause Pesach to wander its way through the solar year and occur in all seasons.

The Two “Other” Calendars

There are three calendars commonly in use in the world today, two of which make no attempt to resolve the discrepancy between solar and lunar years.

The most common secular calendar (the Gregorian calendar) is based solely on the sun. Although the year is nominally broken into twelve months, the use of the word “months” here is a significant departure from its original meaning; according to this calendar, months have no relationship to the cycles of the moon. Most secular months have 31 days, while the lunar cycle is only about 29½ days; and even secular months that have 30 days do not relate to any phase or change in the moon. Similarly, the length of February as a month of either 28 or 29 days has nothing to do with the moon. Thus, although the word month should correspond to the moon, the Western calendar is purely a solar one, with a borrowed term, “month,” given a meaning detached from its origin.

Another calendar that is seeing increased use today is the Muslim one, which is purely a lunar calendar of twelve lunar months, some 29 days and some 30. In truth, a pure lunar calendar such as the Muslim calendar has no real “year,” since a year is based on the relative locations of the sun and the Earth and the resultant seasons, and the Muslim year completely ignores seasons. The word “year” is used in the Muslim sense only as a basis for counting longer periods of time, but has no relationship to the sun.

Thus the Muslim “year” is only 354 or 355 days long — almost eleven days shorter than a solar year. Therefore, a Muslim who tells you that he is 65 years old is really closer to 63 according to a solar year count. He has counted 65 years, each of which is at least ten days shorter than a real year. (I trust that Guinness takes these factors into account when computing world records for longevity and such.)

It is noteworthy that although the Muslim “year” does not correspond at all to a solar or Western year, it corresponds closely to our Jewish year in an “ordinary” year (a twelve-month year, as opposed to a leap year that has thirteen months). And the Muslim month usually coincides with a Jewish calendar month. (We will soon explain why there is sometimes a discrepancy of a day or two.) Thus, for the last three years, the Muslim holy month of Ramadan has corresponded to our month of Elul; but this year, which is a leap year, Ramadan will fall in Av.

It is accurate to say that the Muslim year “wanders” its way through the seasons, as it takes 33 years until a specific month returns to the exact same point in the solar year in the previous cycle; in the interim that month has visited each of the other seasons for several consecutive years. Therefore, Ramadan will not coincide with Elul again this generation. Rather, it will correspond to Av for the next three years, and then to Tammuz for two years, and then to Sivan, etc.

 

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