The Jewish Calendar
Most people have heard of Jewish Holidays such as Passover, Hanukkah and Rosh HaShana as well as Shabbat. In addition, most people know when these holidays occur, during the spring, winter, fall and at the end of each week, respectively. However, the calendar that ensures that these holidays are celebrated during their proper seasons is less well-known.
The Jewish calendar is a Lunisolar Calendar, also known as a fixed lunar calendar. It is a twelve month calendar but the months vary in length with five months being 29 days in length, five months being 30 days in length and the final two varying between 29 or 30 days, depending on the year. The calendar has 354 days as opposed to the Gregorian calendar’s 365 days. Because of this discrepancy, a thirteenth month is added once every two or three years, creating a year about 383 days in length.
The reason why the months are shorter and why the months of Kislev and Cheshvan are flexible in their lengths is to avoid problems with violations of Shabbat and holidays. In addition, there are specific rules as to what days a holiday may fall on. For example, Rosh HaShanah may not occur on Sunday, Wednesday and Friday while the last day of Sukkot – Hoshana Rabba – may never be on Shabbat. Passover may not fall on Monday, Wednesday and Friday.
Holidays on the Calendar
Each of the Jewish Holidays fall out during specific days of the week. The first day of Passover may be on Shabbat, Sunday, Tuesday and Thursday. Rosh HaShana and Sukkot may be on Monday Tuesday, Thursday or Shabbat. Yom Kippur can occur on Wednesday, Thursday, Shabbat or Monday. Chanukah may start on any day other than Tuesday.
Names of the Months
The Twelve Months are referred to by their numerical sequence in the Torah as are the days of the week, although there the Canaanite names for the first, second, seventh and eighth months are mentioned in specific locations as Aviv, Ziv, Ethanim and Bul. Currently, the days of the week are still referred to by their numerical order; the months of the Jewish calendar have Babylonian names. Those names are: Nissan, Iyar, Sivan, Tammuz, Av, Elul, Tishrei, Cheshvan (or Marcheshvan), Kislev, Tevet, Shevat and Adar.
Leap Years and Holidays
Because Jewish Holidays are to occur during specific seasons, it is frequently necessary to ad a thirteenth month to the calendar. This month, a second Adar 30 days in length, is added in the late winter. This reason for this is to ensure that Passover is in the spring, which traditionally was determined by the ripening of barley. The insertion of this month effectively causes all Jewish holidays to occur approximately one month later on the Gregorian calendar: Passover occurs late April, Shavuot falls out during June, Rosh HaShana, Yom Kippur and Sukkot are all during October and Hanukkah is during the end of December.
However, the holiday that is most affected is Purim. Purim is celebrated during Adar. During a leap year, the Purim celebrations are pushed off to the second Adar and the first Adar is considered to be the extra month.
Day Starts at Night
In Judaism, the day starts at night. This affects Jewish Holidays in that they begin the evening before the day starts. For an example, take Rosh HaShana, which is the first day of the year. Because the day starts at night, the holiday actually begins at nightfall on the last day of the year. The same applies for Passover and other holidays. Shabbat has this rule too and therefore begins Friday night and ends Saturday night.
The day beginning at night also affects man’s ability to perform labor. Because the Jewish Holidays have the same restrictions as Shabbat regarding work, the prohibition actually begins at night.