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The Hebrew Calendar

The Jewish calendar is a complicated affair, and it evolved over a long period of time. The calendar is luni-solar, which means that it is composed, nominally, of twelve lunar months (which add up to 355 days). This is the "luni" part of the calendar. However, to keep the calendar in line with the seasons (355 days falls short of the solar year by about 10 days), an additional lunar month – called an intercalary month – is added every few years. This is the "solar" part of the calendar.

In ancient times, the dating of the months was based on observation (of the new moon's crescent in the western sky at evening). The addition of intercalary months was probably by consensus among the Hebrew leaders, as they gauged whether Nisan coincided with the spring season, as determined by the ripening of barley (the earliest grain). If this had not occurred, another month was added, to make Nisan so coincide. Some time after the 7th century BC, intercalary months began to be applied by formula rather than by observation. By the 4th century AD the calendar became fixed.

The Babylonian exile, beginning in the 6th century BC, had a great influence on the Jewish calendar. The months, which had been generally designated by numbers or by agrarian terms, began to be called by their Babylonian equivalents, and the rarely used Hebrew names disappeared. Also, the New Year, which had been celebrated in Nisan, was moved to Tishri, when the Babylonians celebrated theirs.

The present Jewish calendar is still a luni-solar one, whose new year still begins in Tishri. The calendar day consists of 24 hours, each hour being divided into 1080 parts, equal to about 3.3 seconds each. The new day is considered to begin at sunset. The assigning of intercalary months is done within a recurring 19-year cycle (because 19 solar years comprises exactly 235 lunar months). For the Hebrew calendar, the intercalary month is placed before Nisan, and it is designated as Adar II. It is used in the 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years of the recurring cycle. These are called leap years.

The calendar also conforms to strict religious limitations. For example, the New Year must not fall on a Sunday, Wednesday or Friday. The Day of Atonement must not fall on a Friday or Sunday. The Day of Tabernacles must not fall on a Saturday. Passover must precede the New Year by 163 days, and Pentecost must precede the New Year by 113 days.

The month is still calculated from new moon to new moon, a period of about 29½ days. To adjust for the half-day, a system of alternating 29 and 30-day months is used. The months containing 30 days are called "full" and those containing 29 are called "defective." The lengths of most months are fixed. However, two of the months are variable to ensure the religious requirements are met. Also, the length of Adar, which is normally 29 days, increases to 30 days in a leap year (when Adar II is used). The listing below outlines the design:

As mentioned, the length of the year varies to accommodate the religious requirements. A "complete" year is one in which both Heshvan and Kislev are full. It will have 355 days in an ordinary year or 385 in a leap year. In a "normal" year Heshvan is full and Kislev is defective, and there will be 354 or 384 days. Both months will be defective in a "defective" year, in which there will be 353 or 383 days. So, in total, there are six possible year lengths.

If this was the only design criterion (whether the years were complete, normal, or defective), there would only be six arrangements of the Hebrew year. However, there are fourteen, owing to the religious requirements. These fourteen arrangements can be grouped as follows:

Each of the above arrangements has been assigned a "Calendar Number." Their characteristics are as follows:

 

Calendar No. 1 355 days year begins on a Monday
Calendar No. 2 353 days year begins on a Monday
Calendar No. 3 354 days year begins on a Tuesday
Calendar No. 4 355 days year begins on a Thursday
Calendar No. 5 354 days year begins on a Thursday
Calendar No. 6 355 days year begins on a Saturday
Calendar No. 7 353 days year begins on a Saturday
Calendar No. 8 385 days year begins on a Monday
Calendar No. 9 383 days year begins on a Monday
Calendar No. 10 384 days year begins on a Tuesday
Calendar No. 11 385 days year begins on a Thursday
Calendar No. 12 383 days year begins on a Thursday
Calendar No. 13 385 days year begins on a Saturday
Calendar No. 14 383 days year begins on a Saturday

 

Listed below are the Calendar Numbers that apply to the Hebrew years that encompass the period from 1993 to 2013 (the date to the right of the Calendar Number is the Gregorian date for 1 Tishri). Note that the Hebrew calendar begins at the supposed year of Creation, being 1 Anno Mundi (AM), which corresponds to 3761/3760 BC in our Western calendar.

 

5754 AM 1993/94 Cal No. 4 Thu 16 Sep, 1993
5755 AM 1994/95 Cal No. 10 Tue 6 Sep, 1994
5756 AM 1995/96 Cal No. 1 Mon 25 Sep, 1995
5757 AM 1996/97 Cal No. 14 Sat 14 Sep, 1996
5758 AM 1997/98 Cal No. 5 Thu 2 Oct 1997
5759 AM 1998/99 Cal No. 1 Mon 21 Sep, 1998
5760 AM 1999/00 Cal No. 13 Sat 11 Sep, 1999
5761 AM 2000/01 Cal No. 7 Sat 30 Sept, 2000
5762 AM 2001/02 Cal No. 3 Tue 18 Sep, 2001
5763 AM 2002/03 Cal No. 13 Sat 7 Sep, 2002
5764 AM 2003/04 Cal No. 6 Sat 27 Sep, 2003
5765 AM 2004/05 Cal No. 12 Thu 16 Sep, 2004
5766 AM 2005/06 Cal No. 3 Tue 4 Oct, 2005
5767 AM 2006/07 Cal No. 6 Sat 23 Sep, 2006
5768 AM 2007/08 Cal No. 12 Thu 13 Sep, 2007
5769 AM 2008/09 Cal No. 3 Tue 30 Sep, 2008
5770 AM 2009/10 Cal No. 6 Sat 19, Sep 2009
5771 AM 2010/11 Cal No. 11 Thu 9 Sep, 2010
5772 AM 2011/12 Cal No. 5 Thu 29 Sep, 2011
5773 AM 2012/13 Cal No. 2 Mon 17 Sep, 2012


The Hebrew calendar is used today in Israel for all civil and religious purposes, and by Jews around the world for religious purposes. The holy days of the modern Hebrew calendar are:

 

Tishri I Rosh Hashana, New Year, Feast of Trumpets
Tishri 3 Tzom Guedaliah, Fast of Guedaliah
Tishri 10 Yom Kippur, Day of Atonement
Tishri 15 Feast of Tabernacles
Tishri 21 Sukkoth (last day of the Tabernacles festival)
Tishri 22 Feast of the 8th day
Tishri 23 Simath Torah, Rejoicing of the Law
Kislev 25 Hanukkah, Dedication of the Temple, Feast of Lights
Tebet 10 Asarah B'Tebet, Fast, Siege of Jerusalem
Adar 13 Fast of Esther (to fall in Adar II when used)
Adar 14 Purim (to fall in Adar II when used)
Nisan 15 Pesach, Passover
Sivan 16 Shevouth, Pentecost
Tammuz 17 Shiveah Asar B'Tammuz, Fast, Taking of Jerusalem
Ab 9 Tishah B'Ab, Fast, Destruction of the Temple


From the preceding tables, we can determine Hebrew-Gregorian equivalents. For example, the Hebrew year 5761 AM corresponds to the year-range 2000/01. This Hebrew year contains 353 days and begins on a Saturday (Cal No 7). The first day of Tishri for that year (New Year's day) corresponds to September 30, 2000.

If you wished to determine the Gregorian date for, say, the Feast of Purim in the year 2002, you would proceed as follows. First, Purim occurs on 14 Adar (when Adar II is used, Purim occurs on 14 Adar II). Since Adar corresponds to the February-March period, we know (from the preceding tables) that the Hebrew year associated with February-March 2002 is 5762 AM. That particular year is a Calendar Number 3 year of 354 days (a "normal year") wherein the variable months of Heshvan and Kislev contain 30 and 29 days respectively. Having found the lengths of those two months, we can now determine that 14 Adar will occur on the 162nd day of that Hebrew year (162 = Tishri 30 + Heshvan 30 + Kislev 29 + Tevet 29 + Shevat 30 + Adar 14). Since the new year began on Tuesday 18 Sep, 2001, working forward 162 days from that date takes us to February 26, 2002. This is the Gregorian date for the Feast of Purim in the Hebrew year 5762.

Of course, the above calculations are time-consuming. Thankfully, there are Internet sites available where calendar conversions between Hebrew and Gregorian (or Julian) dates can be done very quickly. Shareware is also available, such as "Hebrew Calendar" (see: http://www.calendar-maven.com/ ).