The Origins of the Jewish Calendar

By | Jun 29, 2020
Jewish World, Summer Issue 2020

For centuries, the Jewish calendar has unified the Jewish people. The dates of Jewish holidays have set common temporal landmarks for Jews, wherever they may live. But before the development of the calendar we know today, sectarian debates and geographical separations created calendrical disputes that deeply divided Jewish communities. Moment’s Lilly Gelman talks about Jewish time with Sarit Kattan Gribetz, an assistant professor of theology at Fordham University and author of the forthcoming book Time and Difference in Rabbinic Judaism.

How does the Jewish calendar compare with those of other cultures and religions?

The Jewish calendar is a lunar-solar calendar, which means that the months are based on the moon’s cycles, but the years are adjusted to the annual seasons based on the earth’s rotation around the sun. In certain years, a leap month is added so that the years stay coordinated with the seasons. That’s different from the Muslim calendar, which is a lunar calendar, and from the Christian calendar, which is a solar calendar.

Why did the calendar develop this way?

The Torah lists major holidays and mentions months of the year. It also states that holidays are celebrated on certain days of those months, but not whether those months are lunar or solar months, so it’s hard to reconstruct the calendar of early communities. In the Second Temple period, however, there were dramatic disputes among different sects about what shape the calendar should take.

The apocalyptic sect living in Qumran, for example, advocated for a solar calendar of 52 weeks, with seven days for each week, while other groups favored a lunar or a lunar-solar calendar. The stakes of that disagreement were high because if you are committed to fulfilling the commandments of sacred texts, and those texts insist that you celebrate a festival on a certain day—if you’re using the wrong calendar, you can’t synchronize your time with God’s time.

What was eventually adopted?

According to the Mishnah, the early rabbis adopted an observed lunar calendar—a calendar where witnesses would come to the rabbis to declare that they saw the new moon and the rabbis would then officially declare the beginning of a new month. In the Mishnah, there is a story of witnesses coming to Rabban Gamliel and telling him that they observed the moon. The rabbi accepts their testimony and declares a new month. But the next day two other witnesses come and contradict the original testimony. Rabban Gamliel basically responds, “It’s too bad because I already declared it and we’re not going to change it.” Scholars point to this text and others like it as examples of how rabbinic figures approached the calendar. Rather than regarding the calendar as something that God controlled and people needed to make sure they got right, they started thinking of it as something that was in human hands. People needed to do their best to set the calendar, and once they set the calendar, God would adjust.

Time can function to both unify the Jewish community and also separate it from other communities.

Over the course of the rabbinic period, the calendar goes from being an observed calendar based on witnesses to a calculated calendar. This history has been extensively studied by my colleague Sacha Stern, at University College London. We don’t know exactly when this shift occurred, but we know it didn’t happen overnight. Rather, additional rules about declaring new months were gradually made (for example, how many days different months could have and on which days certain festivals could or could not fall), which meant that even while the rabbinic calendar remained empirical, the rules governing that process became more fixed and the calendar became more predictable. These early calendrical rules laid the groundwork for what eventually became a fixed rabbinic calendar, which meant that the start of new months were calculated, based on astronomical and mathematical formulae, rather than determined by observation. And though the calendar became calculated, not everyone agreed on the same calculations. Palestinian and Babylonian rabbis disagreed about the ways that calendrical calculations ought to be made, and who had the authority to make those calculations. Also, not all Jewish communities followed the rabbinic calendar, either because they were beyond the geographical scope of rabbinic communities (for example, in Alexandria) or because they disagreed with rabbinic principles (such as the Samaritan and Karaite communities). These debates didn’t end in antiquity, either. One of the most interesting debates took place in the 10th century between the Jewish communities of Palestine and Babylonia, which resulted in one year when the two communities observed festivals on different days.

It doesn’t sound as if the calendar always brought people together.

We often think that shared calendars cultivate shared identities and a unified sense of community, and calendars and schedules definitely can do that.

But calendars—and the organization of time more generally—also divide groups from one another. For example, at various points in Jewish history, which calendar you adhered to marked you as a member of one community instead of another. Maintaining a Jewish calendar also became an important way for Jewish communities to preserve their uniqueness and separation from other peoples they lived among. This was already true in the rabbinic period when many Jews lived in the Roman Empire. Rabbinic texts are quite insistent that Jews should maintain their own calendar, celebrate their own holidays and mark their own beginnings and ends of months. They even mandate that Jews should not celebrate Roman festivals, though there is abundant evidence that many Jews did. Rabbinic texts also explicitly comment on how maintaining Jewish time was a way to distinguish Jews from others. One rabbinic midrash declares, for instance, that when the sun is in eclipse, it’s a bad omen for gentiles because they reckon time according to the sun, and when the moon is in eclipse, it’s a bad omen for Jews because they reckon time according to the moon. There’s already an awareness in early rabbinic sources that time can function to both unify the Jewish community and also separate it from other communities. I think that this is the case not only in antiquity, but also today.

You have written about how ancient Jewish sources used women’s bodies as metaphors for time. How did the role of women in the Jewish tradition affect the development of Jewish time?

One of my favorite texts from antiquity is an apocalyptic text called 4 Ezra, written at the end of the 1st century. The story opens with the scribe Ezra, who can’t sleep because he’s distraught about the destruction of the Temple. In his sleepless state, he has a series of visions in which he asks the angel Uriel when the redemption is expected to occur. Uriel responds by explaining that there are some things that humans can’t know, and that the time of redemption is one of those things. But Ezra doesn’t give up so easily. The angel then turns to the metaphor of pregnancy and says, “Go ask a pregnant woman if she knows when labor is going to start.” Of course, Ezra says, “A pregnant woman doesn’t know when labor will start.” Then Uriel responds, “Ask her if she can bring it on sooner.” Ezra acknowledges that doing so is almost impossible. This conversation between Ezra and the angel becomes a meditation on waiting. There are other examples, too, of observing the moon and menses in similar ways.

Rabbinic sources also think about time and gender on a practical level. For example, they discuss men and women’s differing relationships to time and how that affects the kind of religious practices they can or should engage in. There is a passage in the Mishnah that says that all commandments can be subdivided into four categories. There are positive and negative commandments, and there are time-bound and non-time-bound commandments. What we end up with are positive time-bound commandments, positive non-time-bound commandments, negative time-bound commandments and negative non-time-bound commandments. When the Mishnah explains this division, it states that everyone is obligated in all of these categories of commandments, with one exception: Women are not obligated in the positive time-bound commandments.

We end up with a situation in which men are obligated in rituals that need to be performed at a particular time of the day, while women are exempt from those practices. As rabbinic texts present it, men are more tied to ritual time. But that isn’t the end of the story, because in those very same texts, women are associated with other kinds of time—for example, they must observe menstrual purity laws. So although women aren’t obligated to recite the Shema every morning and evening as men must, they do need to be cognizant of the rhythms of their own bodies because they are required to maintain ritual purity. Whether or not the rabbis intended for this to be the case, the result is gendered time: men’s time and women’s time—with different rituals.






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5 thoughts on “The Origins of the Jewish Calendar

  1. Miss C Trainque says:

    Also the idea of a 7-day week was taken from the Babylonians while the Jews were held captive there. Also…on the Jewish calendar are seven months whose names are direct from the Babylonian calendar.

    1. The Jews were held captive by the Egyptians and yet they apparently were familiar with the 7 day week. They were told by God to gather manna for 6 days but on the 7th day they couldn’t. Where were the babylonians then Miss C Trainque?

      1. James Reid says:

        The Royal Kemetic Calendar is about 13,ooo years old and Moses was trained in all ways of Kemetan people so it seems to me that is where the Hebrews got their ideas about their calendar

  2. Kathy Allred says:

    Just learning about the Jewish calender. So much to learn.

  3. Aaron Hauptman says:

    The 7 day week is set forth in the Torah. In he first chapter of the first book of the Torah, B’reishit (a/k/a Genesis), it narrates that G-d created the world in six days and rested on the seventh day (although G-d’s days may not measure the same as human days). Then latter the Torah states in the fifth of the Ten Commandments that Jews shall/may work for 6 days but must rest/refrain from work on the seventh (Sabbath) day, thus setting a 7 day week. This seven day week was promulgated centuries before the Babylonian exile.

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