How do they know when Jewish Holidays are supposed to take place? Simple. There’s a calendar. But where did it come from? Finding it in the Bible is going to be a bit difficult, since the Torah doesn’t exactly specify how the Jewish calendar should be constructed, or on what it should be based. There are generally two options – the sun, or the moon. The Gregorian calendar is based on the sun. The Islamic calendar, the moon. As the Jewish people are far more ancient than both the Christian and Muslim civilizations, the story surrounding their calendar is a bit more complicated.

Leaving the question of what the calendar was based on during the first Davidic commonwealth aside, the big dispute surrounding the nature of the Jewish calendar erupted during the Second Temple era, when the warring factions of the Pharisees and Saducees were vying for control of the central government. It centers around a seemingly irrelevant detail in the verse concerning the counting of the Omer, a 49 day period where Jews count up from Passover to Shavuot, the holiday of the giving of the Torah.

The verse states, in chapter 23 of Leviticus, “After the Sabbath, count 50 days from when you bring the Omer offering.” The question is, what does “after the Sabbath” mean? The Saducees held that it means after a Saturday, meaning that the counting of the Omer must always begin on a Sunday. The Pharisees held that it actually means the Sabbath of the first day of Passover, when no work is done just as on a Saturday Sabbath. This means the counting of the Omer could begin on any day of the week, including the Sabbath itself. In fact, when this happened, it was a big deal, because the cutting of the Omer, a measure of barley, took place on a Sabbath, when harvesting is otherwise prohibited, but the Pharisees made it into a big show that they were specifically cutting on Sabbath, in order to demonstrate that the Saducees were wrong.

Sounds benign and nitpicky, right? It is anything but. This, in fact, is a heated argument about the very nature of the Jewish calendar. Yes, before the Jewish people were arguing about what kind of Kippah to wear, knitted kippa or velvet kippa, they argued about their calendar.

Why is it that the Saducees were so interested in having the counting of the Omer fall out on the same day every year? Because, my Judaica savvy friends, if one holiday falls out the same day of the week every year, all holidays do. But in order for that to happen, you need the number of days in your year to be divisible by 7 exactly. 364 serves that purpose rather well. But what about the extra day? How do you make up the difference?

The answer, for the Saducees, was the Jubilee year, which, according to the Bible, takes place once every 49 years, the same number of weeks as counted in the little detail that started this whole mess. The question is, how long is the Jubilee year? The answer is, again, unclear, at least according to the written Torah. The Saducees held that it is simply a 49 day year that makes up for the lost time of the previous 49 years. The Pharisees, however, held that it is an entire year, which biblically makes more sense, since the Torah forbids sowing the land in the Jubilee year, but makes assurances that there will be enough food. If it were only 49 days, no assurances would be necessary.

In the end, the argument is whether the Jewish calendar is solar, or lunar based. The Saducees wanted solar, wanted all holidays to fall out on the same day of the week every year, and wanted everything determined. The Pharisees, who won the battle, wanted the calendar both solar AND lunar based, with leap months in 19-year cycles to offset the difference.

The proof that the Pharisees were right comes from astronomy. There’s an extra quarter day that the Saducees never accounted for, which equals out to about 12 days every Jubilee cycle. After two cycles, your solar calendar is totally offset, which means that the Saducees, indeed, did not last long as a sect.

The Pharisaic calendar deals with astronomical realities fully, and is the basis for our calendar today.