The Hebrew calendar (Hebrew: הלוח העברי ha'luach ha'ivri) or Jewish calendar is a lunisolar calendar used by Jews, now predominantly for religious purposes. It is used to reckon the Jewish New Year and dates for Jewish holidays, and also to determine appropriate public reading of Torah portions, Yahrzeits (dates to commemorate the death of a relative), and daily Psalm reading, among many ceremonial uses. Originally the Hebrew calendar was used by Jews for all daily purposes. During the era of the Roman occupation (1st century BCE), Jews began additionally following the imperial civil calendar for civic matters such as the payment of taxes and dealings with government officials.
The principles of the Hebrew calendar are found in the Torah, which contains several calendar-related commandments, including God's commandment during the Exodus from Egypt to fix the month of Aviv as the first month of the year.[1] The Babylonian exile in the 6th century BCE influenced the calendar, including the adoption of Babylonian names for the months.[2]
Before the destruction of the Second Temple in 70 CE, the calendar was observational, with the beginning of each month determined by the high court based on the testimony of witnesses who had observed a new crescent moon. In the 4th century CE, the court of Hillel II devised a rule-based fixed-arithmetic lunisolar calendar system to achieve the same effect, so that the increasingly scattered Jewish population would be able to determine the precise dates without consulting the high court.[3] The principles and rules of the current calendar are fully described by Maimonides in the Mishneh Torah.
Because of the roughly eleven-day difference between twelve lunar months and one solar year, the year lengths of the Hebrew calendar vary in a repeating 19-year Metonic cycle of 235 lunar months, with an intercalary lunar month added according to defined rules every two or three years, for a total of 7 times per 19 years. Seasonal references in the Hebrew calendar reflect its development in the region east of the Mediterranean Sea and the times and climate of the Northern Hemisphere. The Hebrew calendar's year is longer by about 6 minutes and 25+25/57 seconds than the present-day mean solar year, so that every 224 years, the Hebrew calendar will fall a full day behind the modern fixed solar year, and about every 231 years it will fall a full day behind the Gregorian calendar year.
Years in the Hebrew calendar are labeled with the era designation Anno Mundi (English: in the year of the world, abbreviated AM or A.M.) and are numbered from the epoch approximately a year before Creation. The Hebrew calendar year in early 2009 is 5769.
The Jewish calendar is a lunisolar calendar, or "fixed lunar year," based on twelve lunar months of twenty-nine or thirty days, with an intercalary lunar month added seven times every nineteen years (once every two to three years) to synchronize the twelve lunar cycles with the slightly longer solar year. Each Jewish lunar month starts with the new moon. Although originally the new lunar crescent had to be observed and certified by witnesses, the timing of the new moon is now determined mathematically.
Concurrently there is a weekly cycle of seven days, mirroring the seven-day period of the Book of Genesis in which the world is created. The names for the days of the week, like those in the Creation story, are simply the day number within the week, with Shabbat being the seventh day. The Jewish day always runs from sunset to the next sunset; the formal adjustments used to specify a standard time and time zones are not relevant to the Jewish calendar.
The twelve regular months are: Nisan (30 days), Iyar (29 days), Sivan (30 days), Tammuz (29 days), Av (30 days), Elul (29 days), Tishrei (30 days), Cheshvan (29 or 30 days), Kislev (29 or 30 days), Tevet (29 days), Shevat (30 days), and Adar (29 days). In the leap years an additional month, Adar I (30 days) is added after Shevat, and the regular Adar is referred to as "Adar II".
The first month of the festival year is Nisan. The 15th of Nisan is the start of the festival of Pesach, corresponding to the full moon of Nisan. Pesach is a spring festival associated with the barley harvest.[4] Since the 4th century, intercalations in the Hebrew calendar have been mathematically determined. Prior to the adoption of the fixed calendar, the intercalation was determined empirically:
The year may be intercalated on three grounds: 'aviv [i.e.the ripeness of barley], fruits of trees, and the equinox. On two of these grounds it should be intercalated, but not on one of them alone.[5]
The Bible designates Nisan, which it calls Aviv (Exodus 13:4), as the first month of the year (Exodus 12:2). At the same time, the season of the fall Festival of Booths (Sukkoth), is called "the end of the year" (Exodus 23:16). The Sabbatical year in which the land was to lie fallow, if it was ever observed at all, necessarily began at the time the winter barley and winter wheat would have been sown, in the fall. The Gezer calendar, an Israelite or Canaanite inscription ca. 900 BCE, also begins in the fall. And Josephus, in the first century CE, states that while
Moses...appointed Nisan...as the first month for the festivals...the commencement of the year for everything relating to divine worship, but for selling and buying and other ordinary affairs he preserved the ancient order [i. e. the year beginning with Tishrei]."[6]
So a multiplicity of new years for different purposes has long been in use. By the time of the redaction of the Mishnah (ca. 200 CE), jurists had identified four new-year dates
The 1st of Nisan is the new year for kings and feasts; the 1st of Elul is the new year for the tithe of cattle... the 1st of Tishri is the new year for years, of the years of release and jubilee years, for the planting and for vegetables; and the 1st of Shevat is the new year for trees-so the school of Shammai; and the school of Hillel say: On the 15th thereof.[7]
Modern practice follows the scheme described in the Mishnah: Rosh Hashanah, which means "the head of the year", and is celebrated in the month of Tishrei, is "the new year for years." This is when the numbered year changes, and most Jews today view Tishrei as the de facto beginning of the year. The 15th of Shevat, the New Year of the Trees, has become a popular minor holiday in recent decades.
The Torah contains several commandments related to the keeping of the calendar and the lunar cycle.
The Jewish day is of no fixed length. The Jewish day is modeled on the reference to "...there was evening and there was morning..."[8] in the Creation story. Accordingly, it runs from sunset (start of "the evening") to the next sunset. However, some apply special rules in the arctic and antarctic regions, where the period between sunsets is twelve solar months.
There is no clock in the Jewish scheme, so that a civil clock is used. Though the civil clock incorporates local adoptions of various conventions such as time zones, standard times and daylight saving, these have no place in the Jewish scheme. The civil clock is used only as a reference point - in expressions such as: "Shabbat starts at ...". The steady progression of sunset around the world and seasonal changes results in gradual civil time changes from one day to the next based on observable astronomical phenomena (the sunset) and not on man-made laws and conventions. Instead of the international date line convention, the antimeridian of Jerusalem is used. (Jerusalem is 35°13’ east of the prime meridian).