Monday, July 5, 2010

The Jewish Calendar

Did you ever wonder why the Jewish holidays come out early in some years and later in others? Why are they never at the right time? The Fourth of July is always on the fourth of July. Canada Day is always July first. Election Day is always the first Tuesday after the first Monday in November. Why do the Jewish holidays bounce around the calendar?

Actually, the Jewish holidays come out the same day every year. But that’s if you use the Jewish calendar. And the Jewish calendar only lines up with the regular calendar once every nineteen years. Why is that?

There are two reasons. First, the Jewish months are in sync with the moon (otherwise known as the lunar cycle). The Jewish month always begins with the first appearance of the moon. The fifteenth of the month is always a full moon. Every month is always exactly the same.

But the Jewish calendar needs to be in sync with the sun – or the solar cycle – as well. The problem is that a year – or twelve months of a lunar cycle – is only 354 days. That is eleven days shorter than a solar year of 365 days.


If you loose eleven days every year, you don’t have a lunar calendar, you have a loony calendar!

Think about it. Passover is supposed to be in the spring, but next year it is eleven days earlier. And the next year it is even eleven days earlier than that. Next thing you know and Passover is in the winter, and then the fall, and then in the summer, and then back in the spring again. It only gets back to where it is supposed to be once every thirty years. Yikes!

To solve this problem, the Jewish calendar adds a leap month about once every three years (technically it is seven times over a nineteen year cycle). At first glance a leap month sounds crazy. But when you consider that the calendar looses eleven days every year, in three years you lost a month. If that is the case, adding an extra month isn’t a big deal.

And because the Jewish calendar is always either loosing eleven days or adding an extra month, the holidays bounce around the regular calendar and either come out early or late.

But really they aren’t early or late at all – they are right on time. They are just connected to the moon and adjusted for the sun. Not the other way around.


  1. Regular calendar?

  2. Solar, Gregorian, standard Western - you know what I am saying....