Jewish months are lunar, which means they can be either 29 or 30 days (because a lunar cycle is about 29.5 days long). In ancient times, the length of each month was determined by observation — when two witnesses attested to the court in Jerusalem that they had seen the new moon, the court would declare it the first of the next month. Immediately, word had to be sent out to Jews in more remote parts of the country and the world so that they could know the date. This was especially important for the six months of the Jewish year that contain an important holiday, ensuring that Jewish communities far and wide would all celebrate the holidays on the correct day.
Of course, for Rosh Hashanah, which falls on the first of the month of Tishrei, it would be difficult to get the word out on time. But not to worry, we learned yesterday that:
Rav said: From the days of Ezra and onward, we have never found that the month of Elul had an additional day.
The month of Elul precedes Tishrei. Rav is saying that for centuries Elul has always (miraculously?) been a predictable 29 days. This means that if communities knew when Elul began, they could calculate the correct date for Rosh Hashanah (and the other Tishrei holidays of Yom Kippur and Sukkot) without waiting for word from the Jerusalem court on the first of Tishrei, which would almost assuredly not arrive on time. In fact, given this, why would we ever send messengers out to announce a new month on Tishrei?
As we see today, the Gemara is skeptical of Rav’s confidence that Elul always has 29 days. In fact, here’s what we find:
When Ulla came from the land of Israel to Babylonia, he said: This year they added an extra day to the month of Elul (making it 30 days long). Ulla continued and said: Do our Babylonian colleagues understand the favor we did for them?
Not only does Ulla’s news indicate that Elul was 30 days in that particular year, he explains that the rabbis made this adjustment on purpose so that Rosh Hashanah would not fall on a day adjacent to Shabbat.
Why would we care if Rosh Hashanah and Shabbat are adjacent? When the two fall alongside one another, the protracted prohibition on labor can become cumbersome for people. As the Gemara explains:
Ulla said: Due to the vegetables that would not be picked for two days and those picked beforehand that would no longer be fresh.
Rabbi Aha bar Hanina said: Due to the dead who would not be buried for two days and consequently would begin to decompose.
While contemporary Jews who observe Shabbat and festival work prohibitions could likely produce a much longer list of the burdens of a multi-day holiday, the Gemara’s focus on harvesting and preserving produce and timely burial of the dead makes sense for its era.
Ulla’s testimony that the rabbis declared Elul to be 30 days long in a given year suggests that there is some tension between the notion that the festival is observed according to the state of the moon and the idea that the rabbis can exercise some control over the calendar. It also contradicts Rav’s notion that Elul is always 29 days.
Rav’s statement of historical “fact” (Elul is always 29 days) also appears on both Beitzah 6 and Beitzah 22. In those instances, Ulla’s counterexample is not brought up at all. So, if you studied only Tractate Beitzah, but not Rosh Hashanah, you might have assumed that the rabbis all agree that Elul is 29 days. As is so often the case, reading more teaches us that the rabbis agree less.
Today we use a calendar established by Hillel II in the fourth century that fixes Elul at 29 days, effectively handing Rav the victory. But as Ulla reminds us, this wasn’t always so.
Read all of Rosh Hashanah 20 on Sefaria.