Jews today make use of two calendars – the modern Western calendar and the traditional Jewish calendar. While the Western calendar is followed for all secular and civil purposes, the Jewish calendar is used for religious purposes, such as the marking of Jewish holidays.
Much like the old Chinese calendar, the Jewish calendar runs on a lunar cycle, and has twelve months of 29/30 days. Since the lunar year is about 11 days shorter than the solar year, the Jewish calendar is kept in line with the solar year by adding a second Jewish month “Adar” every four years. So where there is usually only Adar, in this case there is Adar ‘a’ and Adar ‘b’, essentially adding a 13th month to the calendar.
Days in the Hebrew calendar are based on the lunar cycle – they start and end in the evening, and are determined by the time of sunset. For example, the Jewish Sabbath, or weekly day of religious worship, will start Friday night, at the time of sunset, and will end the Saturday night, an hour after sunset, a time at which the stars are clearly visible. This “25-hour day” rule applies for all Jewish holidays .
According to the Jewish bible, the world was created in seven days. Since the Sabbath was created on the seventh day, all other days of the week are named for their relation to the Sabbath. Thus Sunday is “1st day”, Monday is “2nd day” and so on. This terminology stems from the religious view is that the of the days of the week are merely preludes to the Sabbath.
Originally, Hebrew months did not have names, they were simply called the first month, the second month and so on. However, during 6th Century BC, the Jews were held in captivity in Babylonia, which is referred as the Babylonian Exile. The Babylonian Exile had lasting cultural effects on the Jews. Upon their release from captivity, they adopted Babylonian names for their months. They are as follows:
1st month – Nissan (Mar/April)
2nd month – Iyar (April/May)
3rd month – Sivan (May/June)
4th month – Tamuz (Jun/July)
5th month – Av (Jul/August)
6th month – Elul (Aug/September)
7th month – Tishrei (September/October)
8th month – Cheshvan (October/November)
9th month – Kislev (November/December)
10th month – Teveth (December/January)
11th month – Shvat (January/February)
12th month – Adar (February/March)
The Jewish year begins on the 1st of Tishrei, the seventh month. The Jewish calendar counts years from the time of creation, as described in the Jewish Bible.. According to this count the present year is 5,771 years from the creation of the world.
The Jewish calendar years also go through a seven-year cycle called “Shmita”-. According to this cycle, every seven years, a shmita year is declared, which means that the land must rest and no agricultural activity is allowed . All crops that grow during a Shmita year of their own accord are considered to belong to everyone and can be taken freely. As with the days of the weeks, the years prior to shmita are also numbered in accordance to their relation to Shmita year – ie-the first year to shmita, the second year to shmita and so forth.
Calculation of the Calendar and “Second Day Holidays”
Until the 4th century CE, months and subsequently years in the Jewish calendar were calculated based on vetted testimony regarding lunar phases. Witnesses would come to Jerusalem, the capital of Israel, and testify that they had seen the last phase of the lunar month. Based on this testimony, the religious court in charge would determine whether or not the month would last 29 or 30 days.
Because the testimony took place in Israel, the Jews of Israel were required to alert Jews abroad about the proper date through a series of smoke signals performed on mountains. As the news of the official date took some time to reach Jews abroad, religious authorities ruled that Jews living abroad must keep two days of any holiday. This extra day was intended to prevent Jews abroad from accidentally miscalculating the correct date of the holiday, and thus prevent them from possibly breaking the rules of the holiday.
In the 4th century, Hillel the 2nd, the legal leader of the Jews in the Roman Empire, released the secret to calculating the calendar without testimony. Since then, the Hebrew Calendar has been calculated according to a permanent formula without the need for testimony. However because of the importance of maintaining tradition or because of the importance of maintaining the special, holy nature of Israel, for a select few holidays Jewish authorities decided to maintain the original “two-day injunction” for all Jews living abroad.