The Jewish calendar is packed with holidays, and while the secular dates for these holidays may shift from year to year, the Hebrew dates stay the same annually. Pesach starts on the 14th of Nisan, Hanukkah on the 25th of Kislev, and so on. Surprisingly, though, there is one thing in our Jewish tradition that actually tracks the secular calendar.
During the weekday Amida (the standing prayer), for part of the year, we say a prayer requesting rain. In Israel, they start saying this prayer on the 7th of Heshvan. Outside of Israel, however, we begin on the evening of December 4th (or 5th, or even 6th). How can one tradition follow the secular calendar?
To answer this question, we need to understand why we pray for rain and why Israel begins on the 7th of Heshvan. Praying for rain was essential in Israel because of the very limited water sources. The people living there depended entirely on rain for their survival. As soon as the rainy season started after Sukkot, people would begin praying for rain. However, they waited until everyone returned home from Jerusalem, since Sukkot is one of the three pilgrimage festivals when Jews historically traveled to Jerusalem. Sukkot begins on the 14th of Tishrei, and Shmini Atzeret falls on the 22nd of Tishrei. The Mishna in Ta’anit 1:3 teaches that the 7th of Heshvan is 15 days after Shmini Atzeret. This allows Jews traveling to Jerusalem from across Israel enough time to return home before the rains start.
But what about people who traveled to Jerusalem from Babylonia? It took much longer than two weeks to return home to Babylonia. The Talmud offers an answer: Ta’anit 10a:12, commenting on this Mishna, states that in the Diaspora, people do not start praying for rain until sixty days into the season—understood as sixty days after the equinox.[i]
This raises a new question: the equinox occurs on September 20th or 21st, so sixty days later would be November 20th or 21st. Why are we waiting another two weeks?
To answer this, we need to understand how calendar calculations work. Today, we know that the average year lasts 365.2422 days (365 days, 5 hours, 48 minutes, and 46 seconds). In the Talmud, the sage Shmuel set the year at 365.25 days (365 days and 6 hours). This is called the Julian calendar in the secular world, established by Julius Caesar in 45 BCE.
The difference between 365.2422 and 365.25 may seem small (11 minutes and 14 seconds per year), but it adds up over time. After 128 years, the gap is about one day. In a thousand years, it’s 7.8 days!
The Catholic Church took action in 1582. Pope Gregory XIII ordered that ten days be removed from the calendar: the day after Thursday, October 4, became Friday, October 15. The new Gregorian calendar was designed to better match the actual solar year. While the Julian calendar added an extra day every four years, the Gregorian calendar skipped the extra day three years out of every 400. Each Century year is not a leap year unless it is divisible by 400. So, 1900 was not a leap year, but 2000 was, and 2100 will not be. This results in an average year of 365.2425 days—very close to the actual—and it will take about 3,300 years to add an extra day.
The Talmudic calendar, however, remained unchanged. So, in the Talmudic reckoning, the equinox always occurs on September 24. Yet, September 24th on the Talmudic/Julian calendar corresponds to October 7 on the Gregorian calendar. Adding 59 days to October 7 brings us to December 5, the 60th day. Since the Hebrew day begins at sunset, we start reciting the prayer for rain on the evening of December 4th.
If you look in some siddurim, you will find that the date could be the 4th, 5th, or even 6th. In a four-year cycle, the equinox falls at different times.
· Year 1: 3:00 am
· Year 2: 9:00 am
· Year 3: 3:00 pm
· Year 4: 9:00 pm
The fourth year is always a Hebrew year divisible by four, which starts in the civil year before a leap year. When the equinox occurs at 9:00 pm, it is after sundown and already the next day (October 8). Thus, 59 days later would be December 6, and in those years, we begin saying the prayer on the evening of December 5.
The fact that the equinox occurs at 9:00 pm in the year just before the leap year explains why the date remains October 7. Since it will then be 366 days (rather than 365) until the next October 7, the 366-day interval ends on October 7 of the leap year at 3:00 am.
This system works flawlessly until we reach a century year like 1900. Since 1900 was not a leap year (according to Gregorian rules), things changed. The times for the years at the end of the 18th century were:
· October 6, 1896, at 3:00 am
· October 6, 1897, at 9:00 am
· October 6, 1898, at 3:00 pm
· October 6, 1899, at 9:00 pm
Following the rules above, the prayer for rain began at the Maariv service on December 3 in 1896, 1897, and 1898, and at Maariv on December 4, 1899. If 1900 had been a leap year, the date would have reverted to October 6 at 3:00 am, and we would begin the prayer for rain on December 3. However, since it was not a leap year according to Gregorian calendar rules, 365 days after the 1899 date brought the day to October 7, 1900, at 3:00 am, and the prayer for rain began on the evening of December 4.
I also mentioned that we could start saying this prayer on December 6. This happens in a year when December 5 falls on a Friday. Since we don’t say the prayer for rain on Shabbat, we would have to wait until the evening of December 6 in that case.
Since 2000 was a leap year, the shift did not happen. However, 2100 will not be a leap year, so the dates will move one day to December 5/6. The Rabbis are aware of this issue, but they believe that when the Messiah arrives, all such matters will be resolved. If things stay the same, the recitation of the prayer for rain will occur around April in the year 16,800!
The months themselves progress differently from the solar calendar. The average length of the Jewish year over a 19-year cycle is approximately 365 days, 5 hours, 55 minutes, and 25.4 seconds. This is about 6 minutes and 13.4 seconds longer than the average year in the Gregorian calendar. As a result, the average date of the first day of Pesach shifts later by one day every 231 years compared to the Gregorian calendar. It is already, on average, a few days later than when the Jewish calendar was first established.
In the year 15,115, Passover will fall on June 22, which is summer. In 37,258, the prayer for rain will coincide with Passover, which at that time will occur in August or September!
The bottom line is that Jewish calendar reform will be necessary again in the future—or, as the Rabbis believed, the Messiah will come long before then and resolve all such issues.
[i] This calculation was for Babylonia, allowing Jews to return home before the rains started there. What about Jews in other places where the rainy season might be different? The Rosh (Rabbenu Asher ben Yehiel), who compiled an early summary of Talmudic law, suggested that the date should vary for each country based on when the rainy season begins there. However, his idea was not widely accepted.