Unlike the civil calendar, where months do not correspond to ‘moons’, the Jewish calendar observes, both, the 365.25 day sun year, and the 354 day lunar year, which consists of twelve moons. So, as the days of the month pass, the moon waxes until it becomes full in the middle of the month, around the 14th to 16th day, and then wanes. This intimate relationship between the month and the moon, allows us to become aware of the changing phases of the moon.

The trouble is, very few of us tend to know what the Hebrew month is at any time, let alone what day it is. To gauge the extent to which you aware of the Hebrew date ask yourself what date it is today? (Whatever the day is when you read this article). Did you know that on February 1st it was the 27th day of the month of Sh’vat?

As it happens, this February corresponds, more or less, to the 12th month of the Jewish calendar, Adar – yes, the Jewish year for months starts in the spring; not in the autumn, when the Jewish year for years begins. But that’s not the end of the story; the last month of this Jewish year is actually next month because the current Jewish year has 13 months, not 12. So, there is Adar Rishon (or Aleph), the first Adar, and Adar Sheini (or Beit), the second Adar.

The reason for adding a 13th month is to ensure that the moon year does not fall out of step with the sun year, which is 11.25 days longer. If the calendar was not adjusted to keep pace with the sun, the festivals, like Pesach, for example, would no longer take place in the right season. But adding a 13th month is not like adding one extra day to February every four years: In the fourth century, Hillel II established a fixed calendar, still in use today, which standardised the length of months (29 or 30 days – because a lunar month is 29.5 days), and determined the addition of an extra month seven times over the course of a 19 year cycle. The result is that an additional Adar is added in the 3rd, 6th, 8th, 11th, 14th, 17th and 19th years of the cycle. We are currently in the 19th year of the cycle.

As you may be aware, the Festival of Purim is on the 14th day of Adar. In a leap year, it falls in Adar II – so, unfortunately, this means no festival to celebrate this month! Why don’t you spend your time becoming a moon-watcher instead!