Palestinian and Babylonian rabbis disagreed about the ways that calendrical calculations ought to be made, and who had the authority to make those calculations. And though the calendar became calculated, not everyone agreed on the same calculations. 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. 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. We don’t know exactly when this shift occurred, but we know it didn’t happen overnight. This history has been extensively studied by my colleague Sacha Stern, at University College London. Over the course of the rabbinic period, the calendar goes from being an observed calendar based on witnesses to a calculated calendar. Time can function to both unify the Jewish community and also separate it from other communities.
People needed to do their best to set the calendar, and once they set the calendar, God would adjust. 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. 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. But the next day two other witnesses come and contradict the original testimony. The rabbi accepts their testimony and declares 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 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.Īccording 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. 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. In the Second Temple period, however, there were dramatic disputes among different sects about what shape the calendar should take. 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. The Torah lists major holidays and mentions months of the year. That’s different from the Muslim calendar, which is a lunar calendar, and from the Christian calendar, which is a solar calendar. In certain years, a leap month is added so that the years stay coordinated with the seasons. 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. How does the Jewish calendar compare with those of other cultures and religions?