By Israel Drazin
I described in prior essays that Jews, as some other religions, such as Islam, use a lunar calendar and base the dates of their holidays on this calendar. I mentioned some unusual occurrences that transpired because of the use of the lunar calendar. The following is some more information on the lunar calendar.
Jews wanted to harmonize the lunar calendar with the solar calendar because the Bible states that the Passover holiday happens in the spring. If Jews only used the twelve month lunar calendar with each month having either twenty-nine or thirty days, and a year being only about 355 days, Passover would quickly occur in mid-winter. So the Jews devised leap years – seven in every nineteen years – to harmonize the calendars. They added a thirteenth month (called Adar 2) in years 3, 6, 8, 11, 14, 17, and 19. The following resulted:
As I am writing in 2013, the holiday Rosh Hashanah begins as early as September 5. The last time this occurred was over a century ago, in 1899. This is year seventeen in the nineteen year cycle, the longest possible year in the Jewish calendar, 385 days. This early appearance of Rosh Hashanah will not occur for another 76 years, in 2089.
During this long year 2013, or 5774 according to the anno mundi calendar, the first night of Chanukah and Thanksgiving fall on the same day. This is the first time this happened since American President Abraham Lincoln established Thanksgiving in 1863. This overlapping phenomenon will not recur for another 77,798 years.
The Jewish calendar is getting out of sync with the solar calendar, at a rate of 4 days every 1000 years because the solar cycle is not exactly 365 and a quarter days and the lunar cycle is not precisely 29 and a half days. As a result, Chanukah can now be as early as November 28, but in the future the earliest Chanukah will be November 29.
 The use of a lunar calendar that is based on the easily observable lunar cycle may have been prompted by the idea that this is a natural phenomenon and an easy way to divide the year into months.
 Because a lunar cycle is 29 ½ days.
 Many Jews think this is a religious calendar that states the number of years since creation. Actually, it is a calendar that was developed during the early Middle Ages and, as I described in some detail in my essay on the anno mundi calendar, it, like the so-called Christian calendar, is filled with mistakes. According to the Christian calendar, for example, Jesus was born either 4 or 6 years Before Christ.