The Jewish Calendar

A somewhat apocryphal story tells of a Jew who is about to taken in Russia to the ghetto. He manages to ask the local rabbi the following question: if there might be the possibility of smuggling one book to the isolated labor camp, what book should that be? We might imagine the rabbi suggesting a prayer book or possibly the Bible. Yet, the response was “take the Jewish calendar”.

If you know that you are celebrating the various holidays and also keeping the days of communal mourning and fasting, together with the rest of the Jewish community dispersed throughout the world, you have maintained your identity.

Judaism today has a fixed calendar that determines all of its holidays. This is arguably the most important unifying factor in what is otherwise a frequently fragmented religious community. Not withstanding all the disputes, the calendar is universally accepted by all practicing Jews.

The Lunar Months

We have to understand how the calendar functions and what are its components. The basic characteristic of the Jewish calendar is its system for reckoning time and time cycles. The system is commonly described as lunisolar. In other words, it goes both by the moon and by the sun, which is rather complicated. The months of the Jewish calendar are lunar. Each new month is determined by the renewed conjunction of the moon with the sun. That is, the positioning of the moon precisely between the earth and the sun. In other words, the month begins when the moon is totally invisible.

This alignment of sun, moon and earth takes place every 29 days, 12 hours, 44 minutes and 3 seconds. As a result, the Jewish month would be always either 29 days or 30 days.

A lunar year, meaning twelve such lunar months, would extend for approximately 354 days. However, a solar year is the one that determines our seasons. The position of the Earth opposite to the sun is what determines our seasons. A solar year lasts for 365 days. There is an eleven days differential between a lunar year and a solar year. This is crucial for the Jewish calendar. The holidays of the year in the Jewish cycle commemorate, among other things, the seasons of the year. As a result, they are determined by the solar year. Passover, for instance, is, by biblical definition, a spring festival. If the yearly cycle were determined simply by counting 12 lunar months, something very interesting would happen to that Passover. Passover would slowly retreat back from the Spring into Winter.

The Added Month

The problem of the Jewish calendar was to align between the lunar year and the solar year. This was done by adding a 13th month every three years. So, let’s say that at every time that Passover started creeping back into the winter, we would add just prior to Passover a 13th month, moving it again back into spring.

In ancient times, the decision to proclaim such a leap year was taken by recognized authorities. These authorities might have been connected to the Temple in Jerusalem prior to its destruction, and afterwards connected to some sort of Rabbinic institutions. The problem was that different bodies and different persons or authorities often claimed the right to regulate the calendar. This led to some major clashes within the Jewish community.

For instance, the Jews of Babylonia and the Jews of Palestine a number of times clashed among themselves who has the right to determine the Jewish calendar.

The Calendar and the Christian Church

In the 4th century, pressure was placed on the Jewish calendar for the first time by an outside source. This was the young Christian Church. The reason for this was very interesting. Some Christian groups in the Eastern Roman Empire would wait until the Jews proclaimed their Passover to know when to celebrate Easter. Easter happened on Passover. This created a very uncomfortable situation. Does that mean that we have to wait until some rabbis gather together to proclaim their Passover for us to know when to celebrate Easter?

As a result, two things took place. On the one hand, the Church Council of Nicaea in 325 gathered, and one of its goals was to determine a fixed date for Easter that would not be dependent on the Jewish calendar anymore. They came out with that day, and it would be the first Sunday after a full moon in the Spring equinox. By doing this, of course, they dissolved any connection between Passover and Easter, because Passover always falls on the day of full moon.

The Fixed Calendar

There was a pressure being placed on the authorities that were involved not only in proclaiming the Jewish calendar, but then announcing it to the diaspora communities. This is a very interesting phenomenon. Once decisions were made in Palestine, how did the Jewish diaspora found out about this?

We know that, in antiquity, at least in those countries in the immediate vicinity of Palestine, they received words from a system of flares or flames that were lit at the tops of mountains. From Jerusalem towards Jericho. From Jericho up into the Jordan Valley. Then into Syria, then to Iraq.

Ultimately, that system changed for obvious reasons, and messengers were sent. We know that in the 4th century all sorts of interference was being run against these messengers.

Clearly, by the 4th century, there was a need within the Jewish community to establish a fixed calendar. This fixed calendar, according to tradition, was established by one of the heads of the Rabbinic community in Palestine, somewhere around the year 359 C.E. From that time on, Judaism had a fixed calendar. You knew in advance when it would be a leap year and so on. Some centuries later there were still some skirmishes between Babylonia and Palestine regarding the calendar. It is a very very crucial issue, because the calendar really manifests Jewish leadership. The official institutions that regulated the calendar, basically regulated Jewish life throughout the world.

In a normal year, it was decided that it would always be of 12 months, but every three years, a 13th month would be inserted as a leap year.

The names of the Jewish month all go back to the ancient Babylonian period. What is interesting is that these names were universally accepted by Jews until this very day.