The
Hebrew calendar (
Hebrew ???? ??????) or
Jewish calendar is a
lunisolar calendar used by
Jews for predominantly 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, but by the era of the
Roman occupation (1st century BCE), Jews followed the
imperial civil calendar for all 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 Nisan 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 testimony of witnesses who had observed a new crescent moon. Between 70 and 1178 CE a rule-based fixed-arithmetic lunisolar calendar system was adopted to achieve the same effect. The principles and rules of the current calendar were fully described by Maimonides in 1178 CE 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 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. With respect to the present-day mean solar year, the Hebrew calendar's year is longer by about 6 minutes and 25+25/57 seconds, meaning 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. This is due to the 0.6 second discrepancy between the calendric "Molad" (lunar conjunction interval), which is fixed by Jewish Law,[3] and the actual mean lunar conjunction interval, which itself is slowly changing over time.[4]
