God said, "Let there be lights in the expanse of the sky to separate day from night; they shall serve as signs for the set times the days and the years." -Genesis 1:14
Blow the horn on the new moon, on the full moon for our feast day, for it is a law for Israel, a ruling of the God of Jacob. -Psalm 81:4-5
Recently I was at a meeting involving Arabs and Jews and we had to schedule our next meeting. One woman, a non-observant Moslem, began to leaf through her calendar to find out when Id El-fitr falls this year. Id El-fitr is the feast that marks the end of Ramadan, the month of fasting. I said, "It has to come on Rosh Hashanah this year, so it must be right around September 30." She kept on leafing until she found it sure enough, on Rosh Hashanah. My knowledge and the coincidence of the two holidays seemed to surprise her. I find myself surprised anew every time I have an encounter like this. There seems to be an assumption that the Moslem and Jewish calendars operate in some kind of esoteric relationship, so while we know there is a systematic shifting, we would never attempt to figure it out. And yet, actually, the system is not esoteric at all, but is easy to follow. Indeed, the way the Jewish calendar is linked to both the Moslem and the Gregorian calendars makes it a sort of cultural bridge between the two worlds (so what else is new?).
It is fairly well known that the lunar calendar has 12 x 29.5 days, or 354. The solar calendar has of course 365.25 days. And so the lunar calendar gains 11 days on the solar cycle every year. The Gregorian calendar ignores the moon. It is attuned to the seasons. Everybody knows the associations of the months with the climate, and just naming a month arouses visceral memories of the smells and sounds and sights of its particular season. The pure lunar calendar, used by the Moslems, ignores the seasons. Thus, they have no seasonal holidays any given date, like the month of Ramadan for example, will over about 30 years rotate through all the seasons, falling 11 days earlier in the solar cycle every year.
The Jewish calendar blends the two, which means that our months are lunar months, directly attached to the cycles of the moon, while our holidays are fixed according to the seasons of the solar year. We accomplish this by adding a thirteenth month in years 3, 6, 8, 11, 14, 17, and 19 of every 19 year cycle. To know if a year is a leap year, just divide it by 19 and see if the remainder is one of these numbers (e.g., 5768, the year now ending, comes out to 303 with a remainder of 11 and it was indeed a leap year.)
So, we share our new moons with the Moslems. By definition, every month in the Moslem calendar begins on the same day as a month in the Jewish calendar (though we might differ by a day due to disagreement on when the moon is really new). We are in synch. Ramadan will always coincide with a month in the Jewish calendar. Id El-fitr will always be on Rosh Chodesh. It amazes me how many Israelis, Moslems and Jews, don't know that. Moreover, the shift only comes in a leap year. The shift against the solar calendar is a constant 11 days a year, but against the Jewish calendar the shift is a month at a time. So, last year Ramadan coincided with Tishrei. The year was a leap year so it got bumped up to Elul this year. Now it will stay on Elul for the next two years, until in year 14 of our cycle the leap year will lengthen our year by a month and Ramadan will get moved up to Av.
Shanah Tovah! Best wishes for a year of rejoicing in what we have in common with Others and understanding and respecting what we don't.