The Hebrew Calendar, Part 1

The Hebrew Calendar (Part 1)

The Gregorian calendar is the method of reckoning dates used by most of the world. It was sponsored by Pope Gregory XIII n 1582 as a corrected version of the Julian calendar. It is a solar-based calendar in which dates represent the position of the earth in its revolution around the sun.

The Hebrew/Jewish calendar is quite unlike the Gregorian or the Julian calendar. It is a modified lunar-based calendar—that is, based on cycles of the moon phase. It is also adjusted by adding intercalary months (that is, a thirteenth month in certain years) to bring the lunar cycles into synchronization with the solar year.

Trying to understand the Holy Day dates on the Gregorian calendar can be quite challenging. For example, the Feast of Trumpets (Rosh Hashanah) falls on the Hebrew calendar date of Tishri 1. One may wonder why in some years Tishri 1 may fall early in September, while in others it may be as late as October. Having a basic understanding of the modified lunar calendar used by the Jewish people provides us with the answers. In this chapter, I will demonstrate how to reconcile the disparities between the numbers of days in the Jewish and Gregorian calendars.

The calculations used may appear to be a little bit intimidating, with long decimal places and many steps, but they are really very straightforward and simple. Gaining knowledge into the Jewish calendar will greatly assist in understanding why the Holy Days do not occur at the same time on our calendar every year. In addition, learning a completely different way to reckon months and years can be quite interesting.

The major points to note are that the lunar calendar has 29.53 days in a month. Twelve months are equal to approximately 354 days, 11 or 12 days less than twelve months in the Gregorian calendar. To make up for this difference, the Jewish calendar adds a thirteenth month in seven years out of every nineteen, so that the “modified lunar” (lunisolar) calendar and the Gregorian calendar come into almost exact alignment every nineteen years. The table below demonstrates the number of months in a year for the two calendars, representing the current nineteen-year cycle.

Hebrew                       Gregorian
Year   # of Months      # of Months    Year
5758           12                  12             1997
5759           12                  12             1998
5760           13                  12             1999
5761           12                  12             2000
5762           12                  12             2001

5763           13                  12             2002

5764           12                  12             2003

5765           13                  12             2004
5766           12                  12             2005
5767           12                  12             2006

5768           13                  12             2007

5769           12                  12             2008

5770           12                  12             2009

5771           13                  12             2010

5772           12                  12             2011

5773           12                  12             2012

5774           13                  12             2013

5775           12                  12             2014

5776           13                  12             2015

In part II in this series we will determine how well the days between two common calendars can be reconciled.