Rabbanite Calendar
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BibArch Home Up Old or New Cycle Calendar Rules CE 22-40 OC CE 22-40 NC 10 BCE - CE 99 OC

The Rabbinate Calendar is a calculated calendar governed by a set of rules. It is often referred to as the Hebrew Calendar, the Jewish Calendar, or the Hillel II Calendar. Reduction of calendar rules to mathematical statements yields a mathematical model providing a perpetual calendar. Unfortunately, only since the 4th century CE has this method, with all of its intricacies, uncontrovertibly been in use. At that time the rules governing the Hebrew calendar were kept secret, known, and presumably used, only by a select number of the Sanhedrin.

When the persecution of Roman emperor Constantius (337–361) threatened the very existence of the Sanhedrin, the body responsible for officially proclaiming the molad, its president, Patriarch Hillel II, took an extraordinary step to preserve the unity of Israel. In order to prevent Jews scattered all over the earth from celebrating their own new moons, festivals and holidays at their own chosen times, he made public a fixed system of calendar calculation.

The method for determining the moladoth and intercalation of leap months throughout the second temple period (BCE 516—CE 70) and up until the time of Hillel II, as long as there was an independent Sanhedrin, presumably was much more empirical than the methods used today. The priests kept the rules and set the calendar. The Talmudic writings have intercalations being done by some calculation and some observance in the second and third centuries. 

The beginning of the months were determined by direct observation of the new moon, or molad, in Jerusalem. What was observed would have been the first crescent of a young moon since the new moon, i.e., the conjunction, by definition is invisible. The appearance of the young moon would be reported by witnesses to the Sanhedrin. Then these beginnings of each month (rosh hodesh) were sanctified and announced by the Sanhedrin, the Supreme Court in Jerusalem, after witnesses had testified that they had seen the new crescent and after their testimony had been thoroughly examined, confirmed by calculation and duly accepted.

The new moon was set aside as a holiday by the Sanhedrin. The witnesses had to be heard before the afternoon sacrifices or the following day would be declared to be the start of the new month. The obvious problem faced by depending on direct observation of the moon to declare new months is visibility. If the skies were overcast and stormy for a few days at the time of the new moon, a new month could not be declared by direct observation. Hence, the Sanhedrin ruled that months were to be limited to 29 or 30 days, with no fewer than 4 months in a year having either one or the other of these two lengths. Hence, during the Second Temple period the year may have contained as little as 352 to as many as 356 days.

The Calendar Council (Sod Haibbur) of the Sanhedrin regulated the Hebrew calendar by reconciling the calculated solar year and the observed lunar month. Whenever, after two or three years, the annual excess of 11 days had accumulated to approximately 30 days, a thirteenth month, Adar II, was inserted before Nisan in order to assure that Nisan and Passover would occur in the Spring and not retrogress toward winter. But, the remoteness of the spring equinox was only one reason for intercalating a leap month. The other was a late spring. Spring was considered late if crops were not ripe or new-born animals were too young. The Rabbinate Calendar eliminated such factors as it predetermined the calendar for the foreseeable future (at least until an new Sanhedrin could one day be formed).

A year may be embolismic on three grounds-on account of the (state of the green ears of) corn or (that of) fruit (growing on the) trees or the lateness of the tquphah [equinox]. Any two of these reasons may justify an embolismic year, but one of them (alone) does not justify an embolismic year. Since there is some controversy over exactly how and why the Sanhedrin intercalated leap months, we can not know with great certainty when a year was common and when it was embolismic.

It is also possible that months were intercalated by the Sanhedrin to maintain their power. The rules for intercalation were held secret. The Sanhedrin had to sanction each new moon and each new year. Because days and months could be added, the Jews in Jerusalem had to send messengers to the Diaspora to tell them the right day to keep the Feast of Passover. This allowed the Sanhedrin some control over dispersed Jews. It is even possible that one of the rationales used by the pre-Essene movement for splitting from main-stream Judaism in the second century BCE was manipulation of the calendar by the so-called Sons of Zodak, the ruling Hasmonean dynasty.

Just as there were reasons for intercalating a month, there were restrictions on how this could be done. Two leap years were allowed to come in a row, but not three. Adar II, the leap month, also could not be added in a sabbatical year. During a sabbatical year the ground had to lay fallow for the entire year. Requiring the land to be fallow for 13 months instead of 12 would have caused undue hardship for a nation surviving on stored food. For the same reason Adar II could not be added during a time of famine.

Signal fires and messengers were used to communicate the correct day to observe the molad, but communications in the first century C.E. were far to slow to allow the Diaspora to know the correct day with certainty. The Jews of the Diaspora celebrated both days upon which the molad could occur, effectively adding a second day to the new moon, the New Year (Trumpets), Booths (Tabernacles), Passover, and Pentecost to ensure that they were observing the correct day. Many Jews of the first century were uncertain when a molad would be officially declared until well after the official declaration.

The Mishnaic rules governing the Hebrew calendar during the Second Temple period casts grave doubts on the possibility of ever being able to determine on exactly what day of the week on the Gregorian calendar any event recorded in Second Temple time occurred unless there is internal evidence pointing to a specific day. The Talmud appears to preserve the older system of observation of the lunar crescent, if the written record may be understood as reflecting actual procedure. It would seem, therefore, that the system of calendation recorded in the 1st or 2nd century rabbinic texts preserved a system which was in use before BCE 481 and continued in use even after a new one was introduced in Babylonia.

The Talmudic system could not have been adopted until—at the earliest—CE 359, and possibly as late as the seventh century. There can, and have been, extensive computer studies done to determine when selected moladoth occurred. However, this does not mean that the first of the month, as determined by the Sanhedrin, occurred on a computed molad. It could have been delayed by as much as two days if the previous month had twenty-nine days and visibility was poor for that molad. Even with good visibility, if Adar II had been added to the end of the previous year, 30 days would have been added just before Nisan. This would have shifted the week forward by two days. If a predicted molad occurred on a Tuesday, but Adar II had been unexpectedly inserted the year before, the actual molad would have occurred on a Thursday instead.

Page last edited: 04/06/06 09:18 PM

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