At their essence, calendars are ways that societies — sometimes everyone, sometimes a specific group of leaders — collectively decide to order their lives temporally. And because people are complicated and weird, so too are their calendars. Don’t believe me? Check out the French Republican calendar or the Soviet Revolutionary calendar. But while these examples are particularly extreme, all calendars reflect the specific set of values and commitments of their creators. We’re now three pages into an extensive discussion of the Jewish calendar that demonstrates how that’s true for the Jewish calendar.
As we’ve discussed, the Jewish calendar is lunisolar. That means that each month is the length of a moon cycle, but because the lunar cycle and the solar cycle don’t line up perfectly, Jews have long used a system of intercalation in which an extra month of Adar is added to the calendar in some years, keeping the months and festivals in the right seasons.
How did the rabbis know when to intercalate a year by adding an extra month? Yesterday, we saw that a number of situational and environmental factors — from road maintenance to barley maturity — were at play. Those teachings were all focused on the observance of Passover. But the following teaching, relevant instead to Sukkot, came toward the end of yesterday’s daf:
Rav Yehuda says that Shmuel says: The court intercalates the year only if the season was lacking most of the month.
The term “season” (tekufah) can mean a general cycle or turn, but it can also more specifically refer to the annual solstices, the longest and shortest days of the year, and the equinoxes, when the sun appears directly over the equator and day and night are roughly the same length. Here, Shmuel is explaining that the court only intercalates the year if the autumnal equinox is not set to happen after “most” of the month of Tishrei.
And how much is “most of the month”? 16 days — this is the statement of Rabbi Yehuda.
Rabbi Yosei says: 21 days.
And both of them expounded the same verse: “You shall observe … the Feast of Ingathering at the turn (tekufah) of the year.” (Exodus 34:22).
Both Rabbi Yehuda and Rabbi Yosei read the word tekufah in Exodus as a reference to the autumnal equinox. So the Feast of Ingathering (meaning harvest, aka Sukkot) must be observed at the autumnal equinox. But what does “at” mean?
One sage (Rabbi Yehuda) holds that we require all of the festival to take place in the new season (meaning all seven days of the holiday must take place after the autumnal equinox). And one sage (Rabbi Yosei) holds that we require some (meaning at least one of the seven days of the holiday if not more) of the festival in the new season.
The Talmud’s discussion of exactly how the autumnal equinox is meant to relate to the month of Tishrei and the observance of Sukkot will continue. Let’s stop here to reflect on what we can learn about how the rabbis thought about their complex lunisolar calendar.
The calendar is rooted in careful reading of the Torah and a commitment to enacting the biblical vision of time. The Torah describes months connected to the cycle of the moon, but it also describes festivals related to the solar seasons, like planting and harvesting. These two systems of time don’t sync up perfectly, and so the rabbis use their careful reading and creative thinking to create alignment between them.
The rabbis also use their knowledge of Babylonian astronomy. Ancient Mesopotamia was one of the birthplaces of astronomy, and ancient Mesopotamian astronomers observed astronomical phenomena in order to calculate the solar cycle. They could even accurately predict eclipses.
In thinking about how the lunar and solar calendars interact, then, the Babylonian rabbis are both profoundly rabbinic and profoundly Babylonian, combining their deep knowledge of Torah with the best scientific conclusions of their day. Their calendar is complicated, but so is being a Jew in the wider world.
Read all of Sanhedrin 12 on Sefaria.
This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on December 29, 2024. If you are interested in receiving the newsletter, sign up here.
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