The Calendar
By Stan Goodenough
The Jewish calendar is lunar, meaning that it runs according the cycles of the moon, so that the beginning of each month is determined by the "new moon". A new moon occurs when the very first sliver of the moon becomes visible after dark.
In Biblical times the new moon, and the beginning of each month, was determined by observation. When two reliable, yet independent, sources would report to the Sanhedrin (Jewish religious council) the sighting of the first sliver of the new moon, the Sanhedrin would declare that day "Rosh Chodesh", the "head of the month".
The "problem" with the lunar calendar, and the reason why it seems to shift in relationship to the Gregorian, is that a solar year contains approximately 12.4 lunar months. The lunar year thus loses around 11 days every Gregorian year.
An answer was worked out in the 4th century AD by Hillel II through complex mathematical and astronomical calculations. Hillel's solution was to standardize the length of every month (doing away with new moon observations), and to set the Jewish calendar on a 19 year cycle where an extra month is added every 3rd, 6th, 8th, 11th, 14th, 17th, and 19th year in order to realign them with the solar year. That extra month is called Adar II and in the year it occurs it is placed immediately after the month of Adar.
The unusual names of the Jewish calendar months are in fact not Jewish at all. Throughout most of the Tanakh, the months are simply referred to by number. However, the Jewish exiles who returned from Babylon under Ezra brought the names of the Babylonian months with them, and these became the names for the Jewish months.
The Jewish calendar and its relation to Gregorian months:
| Name | Month # | Length | Corresponding Gregorian month |
| Nissan | 1 | 30 days | March - April |
| Iyar | 2 | 29 days | April - May |
| Sivan | 3 | 30 days | May - June |
| Tammuz | 4 | 29 days | June - July |
| Av | 5 | 30 days | July - August |
| Elul | 6 | 29 days | August - September |
| Tishri | 7 | 30 days | September - October |
| Cheshvan | 8 | 29 or 30 days | October - November |
| Kislev | 9 | 29 or 30 days | November - December |
| Tevet | 10 | 29 days | December - January |
| Shevat | 11 | 30 days | January - February |
| Adar | 12 | 29 or 30 days | February - March |
| Adar II | 13 | 29 days | March - April |
NOTE: The years of the Jewish calendar are numbered from the creation of the earth in Genesis 1, and are calculated using the ages of people recorded in the Bible. Also, for obvious reasons, the Jews use BCE (Before the Common Era) and CE (Common Era) instead of BC and AD respectively.
© Israel My Beloved
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