Original Article: "Hebrew calendar" http://en.wikipedia.org/wiki/Hebrew_calendar
Hebrew calendar
From Wikipedia, the free encyclopedia
The Hebrew or Jewish calendar (הַלּוּחַ הָעִבְרִי, ha'luach ha'ivri) is a lunisolar calendar used today predominantly for Jewish religious observances. It determines the dates for Jewish holidays and the appropriate public reading of Torah portions, yahrzeits (dates to commemorate the death of a relative), and daily Psalm readings, among many ceremonial uses. In Israel, it is used for religious purposes, provides a time frame for agriculture and is an official calendar for civil purposes, although the latter usage has been steadily declining in favor of the Gregorian calendar.
The calendar used by Jews has evolved over time. The basic structural features of the early calendar are thought to have been influenced by the Babylonian calendar, including the seven-day week, the lunisolar intercalary adjustment and the names of the months. Until the Tannaitic period (approximately 10–220 CE) the calendar employed a new crescent moon, with an additional month normally added every two or three years to correct for the difference between twelve lunar months and the solar year. When to add it was based on observation of natural agriculture-related events.
Through the Amoraic period (200–500 CE) and into the Geonic period, this system was gradually displaced by the mathematical rules used today. The principles and rules were fully codified by Maimonides in the Mishneh Torah in the 12th century.
Maimonides' work also replaced counting "years since the destruction of the Temple" with the modern creation-era Anno Mundi.
The Hebrew calendar year is longer by about 6 minutes and 25+25/57 seconds than the current mean solar year, so that every 224 years, the Hebrew calendar will fall a day behind the current mean solar year; and about every 231 years it will fall a day behind the Gregorian calendar year. Because of the roughly eleven-day difference between twelve lunar months and one solar year, the length of the Hebrew calendar year varies in the repeating 19-year Metonic cycle of 235 lunar months, with the intercalary month added according to defined rules every two or three years, for a total of seven times per 19 years.
The era used since the middle ages is the Anno Mundi epoch (Latin for "in the year of the world"; Hebrew: לבריאת העולם, "from the creation of the world"). As with Anno Domini, the words or abbreviation (A.M. or AM) for the era should properly precede the date rather than follow it, although this is no longer always followed. AM 5773 began at sunset on 16 September 2012 and ended on 4 September 2013. AM 5774 began at sunset on 4 September 2013 and will end on 24 September 2014. AM 5775 will begin at sunset on 24 September 2014 and end on 13 September 2015.
