|As January draws to its close, we are also making our way through the Hebrew month of Sh’vat. In a “regular” year, the next month, Adar, brings Purim to our congregation near the end of February or the beginning of March. This year, however, the Hebrew calendar contains a 13th month, called Adar II, which pushes Purim to the last days of March and, consequently, will place Rosh Hashana in the year 5785 on the evening of October 2nd, 2024, and the first candle of Chanukah on the evening of December 25th, 2024. This positions the start of Chanukah this year near its latest possible beginning point on the secular Gregorian calendar which governs the reckoning of the days in the Diaspora.
Every year, members of this congregation ask me why the Jewish holidays seem to migrate through the calendar from year to year. I begin by reminding them that the Hebrew calendar fixes the holidays on the same day every year. It is only from the perspective of the secular calendar that our Jewish festivals seem to move from one month to the other. This also reminds us that the migration of our community’s celebrations and remembrances through the calendar has its root cause, not in some arbitrary calculation, but in the difference between a lunar and a solar reckoning of the passage of the year.
In a purely lunar calendar, a year is equivalent to twelve lunar months, about 354 days. In a purely solar year, the year is measured by the average time it takes the earth to return to the same point on its orbit around the sun, about 365 ¼ days. Using an exclusively lunar calendar, accordingly, means a difference of approximately 11 days between a lunar year and a solar year. If we only followed the lunar calendar, this would mean that the Jewish holidays would gradually journey through the seasons, sometimes placing Passover during the winter and Rosh Hashanah in the spring. Since the Bible refers to the first calendar month as Aviv, the Hebrew for “spring,” the rabbis of the Talmud rejected this practice in favor of a calculation that periodically brings a purely lunar calendar into alignment with the solar year so that the Jewish people would always celebrate Passover during the springtime.
To bring the two different calendars into agreement regarding the seasons, the Jewish people in antiquity began intercalating an extra month in the Hebrew calendar in seven out of every 19 years. They did this because, in 19 years, the solar calendar exceeds the lunar calendar by 209 days, equivalent to 7 months. When the Temple still stood, the intercalation was determined according to agricultural conditions in the land of Israel at the time. After the destruction, however, the cycle was fixed with an extra month added every 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years. This cycle, called the machzor katan (the “small cycle”) in Hebrew, and the “Metonic” cycle in English, after the Greek astronomer Meton (sixth century B.C.E.) who calculated that nineteen solar years and 235 lunar months are approximately the same duration. This means that every 19 years, the yahrzeits of the people we remember will bring the secular date and the Hebrew calendar into alignment.
Although the need to reconcile the solar and lunar calendar was recognized millennia ago, the Hebrew calendar we have today was only finalized until 10th century of the Common Era. Our present calendar also prohibits placing Yom Kippur just before or after Shabbat and demands that Rosh Hashanah never fall during the daylight hours of Sunday, Wednesday, or Friday. Other regulations fix the minimum and maximum number of days during a regular year (12 months) and the leap year (13 months). Since an astronomical lunar month may contain either 29 or 30 days (as opposed to the secular calculation of between 30 and 31 days), the length of two months, Cheshvan, and Kislev, vary from year to year to bring the 19-year cycle into agreement with the solar year. All this means that the length of the Hebrew calendar varies from year to year, not to confuse everyone, but to make sure that, when we raise our glasses for the first cup of four at the seder, we are looking forward to the rebirth of spring!
As I look out my window at the snow and ice outside, I am grateful that our people understood the wisdom of keeping our seasons and holidays in alignment. I, for one, treasure our ancient calendar which places us outside the rest of the world’s reckoning of time. It makes me appreciate the ancient wisdom of a life tied to the seasons and cycles of both the moon and the sun. Now that you know more about the reasoning behind our special calendar, I hope you feel the same!