The Jewish Calendar

The Jewish calendar is regulated by both the moon and the sun. On average, the moon revolves around the Earth in 29½ days and the Earth revolves around the sun in 365¼ days, which means that a 12-month lunar year is about 11 days shorter than a solar year. If Jews followed the moon year alone, seasonal festivals, like Pesach, which is supposed to occur in the spring, would occur 11 days earlier each year, and would soon fall out of season.

To ensure that the moon year does not fall out of step with the sun year, the Jewish calendar adds an extra month seven times in the course of a 19 year cycle. Since Adar is the last month of the year, an additional month of Adar is added in the 3rd, 6th, 8th, 11th, 14th, 17th and19th years of the cycle, becoming Adar Rishon, the ‘first Adar’. In this way, the regular month of Adar, which includes the festival of Purim, becomes Adar Sheini, the ‘second Adar’. As a consequence of this adjustment, the first month of the year, Nisan, occurs 11 days earlier each year for two or three years, and then jumps forward 30 days, balancing out the drift.

What is known as the ‘civil calendar’ has long abandoned any correlation between the moon cycle and the months. In the Jewish calendar, however, months are either 29 or 30 days, corresponding to the 29½-day lunar cycle. Rosh Chodesh – literally, ‘head of the month’ – is the first day of a new month. Traditionally, where a month has 30 days, the 30th day is also regarded as Rosh Chodesh, since, technically, the new month begins after 29.5 days. In these cases, two days of Rosh Chodesh are observed. Within Liberal Judaism, however, the first day of the new month alone is Rosh Chodesh.

In ancient times, Rosh Chodesh was very important, second only to Shabbat, and was celebrated as a women’s holiday. During the rabbinic period, the association of women with the new moon was lost, and was only revived with the development of Jewish feminism in the 1980s. Nowadays, much of this revival revolves around the practice of reciting birkat ha-l’vanah, ‘the blessing of the moon’, when the first sliver of the new moon is first sighted – around the 3rd day of a new month. The majority of Jews, however, whether observing one or two days as Rosh Chodesh, do not really celebrate the new moon as such, although they may attend synagogue, where they will read ya’aleh v’yavo, an additional prayer, inserted into the T’fillah, the daily ‘Prayer’, sing psalms of Hallel, and hear an additional Torah portion. Indeed, for most synagogue-goers, awareness of the passing of the months is confined to the announcement that is inserted into the Shabbat morning service preceding a new moon.

So how can we become more aware of the changing moons and the Hebrew months? A simple way is to buy a Jewish diary – which you can order from the Leo Baeck College via the synagogue office! And once you have your diary, why not check the Hebrew date each day, and cloudless skies permitting, step outside and look for the moon.

Rabbi Elizabeth Tikvah Sarah