Hebrew calendar From Wikipedia, the free encyclopedia Ha-Luah ha-Ivri) is a , ַה ַלּוּח ָה ִﬠ ְבִרי) The Hebrew or Jewish calendar 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 present Hebrew calendar is the product of evolution, including a Babylonian influence. Until the Tannaitic period (approximately 10–220 Jewish calendar, showing Adar II CE), the calendar employed a new crescent moon, with an additional between 1927 and 1948 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 in Israel.[1] 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 lunar year is about eleven days shorter than the solar year and uses the 19-year Metonic cycle to bring it into line with the solar year, with the addition of an intercalary month every two or three years, for a total of seven times per 19 years. Even with this intercalation, the average Hebrew calendar year is longer by about 6 minutes and 40 seconds than the current mean tropical year, so that every 216 years the Hebrew calendar will fall a day behind the current mean tropical year; and about every 231 years it will fall a day behind the mean Gregorian calendar year. The era used since the Middle Ages is the Anno Mundi epoch (Latin for "in the year of the world"; from the creation of the world"). As with Anno Domini (A.D. or AD), the words or" , לבריאת העולם :Hebrew abbreviation for Anno Mundi (A.M. or AM) for the era should properly precede the date rather than follow it. AM 5777 began at sunset on 2 October 2016 and will end at sunset on 20 September 2017.[2] Contents 1 Components 1.1 Day and hours 1.2 Weeks 1.2.1 Names of weekdays 1.2.2 Days of week of holidays 1.3 Months 1.3.1 Importance of lunar months 1.3.2 Names of months 1.3.3 Leap months 1.3.4 Constellations 1.4 Years 1.4.1 Anno Mundi 1.4.2 Previous systems 1.4.3 New year 1.4.4 Leap years 1.4.5 Rosh Hashanah postponement rules 1.4.6 Deficient, regular, and complete years 1.4.7 Four gates 1.4.8 Holidays 2 History 2.1 Mishnaic period 2.2 Modern calendar 2.3 Usage in contemporary Israel 3 Other practices 3.1 Karaite calendar 3.2 The Qumran calendar 3.3 Persian civil calendar 4 Astronomical calculations 4.1 Synodic month – the molad interval 4.2 Seasonal drift 4.3 Implications for Jewish ritual 4.4 Worked example 5 Rectifying the Hebrew calendar 6 Conversion between Jewish and civil calendars 7 See also 8 References 9 Bibliography 10 External links 10.1 Date converters Components Day and hours The Jewish day is of no fixed length. The Jewish day is modeled on the reference to "...there was evening and there was morning..."[3] in the creation account in the first chapter of Genesis. Based on the classic rabbinic interpretation of this text, a day in the rabbinic Hebrew calendar runs from sunset (start of "the evening") to the next sunset.[4] In most populated parts of the world this is always approximately 24 standard hours, but, depending on the season of the year, it can be slightly less or slightly more. Halachically, a day ends and a new one starts when three stars are visible in the sky. The time between true sunset and the time when the three stars are visible (known as 'tzait ha'kochavim') is known as 'bein hashmashot', and there are differences of opinion as to which day it falls into for some uses. This may be relevant, for example, in determining the date of birth of a child born during that gap. There is no clock in the Jewish scheme, so that the local civil clock is used. Though the civil clock, including the one in use in Israel, 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. In Judaism, an hour is defined as 1/12 of the time from sunrise to sunset, so, during the winter, an hour can be much less than 60 minutes, and during the summer, it can be much more than 60 minutes. This proportional hour is known as a sha'ah z'manit (lit. a timely hour). A Jewish hour is divided into 1080 halakim (singular: helek) or 1 parts. A part is 3⅓ seconds or /18 minute. The ultimate ancestor of the helek was a small Babylonian time period 1 [5] called a barleycorn, itself equal to /72 of a Babylonian time degree (1° of celestial rotation). These measures are not generally used for everyday purposes. Instead of the international date line convention, there are varying opinions as to where the day changes. One opinion uses the antimeridian of Jerusalem. (Jerusalem is 35°13' east of the prime meridian, so the antimeridian is at 144°47' W, passing through eastern Alaska.) Other opinions exist as well.[6][7] (See International date line in Judaism.) The weekdays start with Sunday (day 1, or Yom Rishon) and proceed to Saturday (day 7), Shabbat. Since some calculations use division, a remainder of 0 signifies Saturday. 1 While calculations of days, months and years are based on fixed hours equal to /24 of a day, the beginning of each halachic day is based on the local time of sunset. The end of the Shabbat and other Jewish holidays is based on nightfall (Tzeth haKochabim) which occurs some amount of time, typically 42 to 72 minutes, after sunset. According to Maimonides, nightfall occurs when three medium-sized stars become visible after sunset. By the 17th century, this had become three-second-magnitude stars. The modern definition is when the center of the sun is 7° below the geometric (airless) horizon, somewhat later than civil twilight at 6°. The beginning of the daytime portion of each day is determined both by dawn and sunrise. Most halachic times are based on some combination of these four times and vary from day to day throughout the year and also vary significantly depending on location. The daytime hours are often divided into Sha'oth Zemaniyoth or "Halachic hours" by taking the time between sunrise and sunset or between dawn and nightfall and dividing it into 12 equal hours. The nighttime hours are similarly divided into 12 equal portions, albeit a different amount of time than the "hours" of the daytime. The earliest and latest times for Jewish services, the latest time to eat chametz on the day before Passover and many other rules are based on Sha'oth Zemaniyoth. For convenience, the modern day using Sha'oth Zemaniyoth is often discussed as if sunset were at 6:00 pm, sunrise at 6:00 am and each hour were equal to a fixed hour. For example, halachic noon may be after 1:00 pm in some areas during daylight saving time. Within the Mishnah, however, the numbering of the hours starts with the "first" hour after the start of the day.[8] Weeks is a weekly cycle of seven days, mirroring the seven-day period of the Book of Genesis in which [שבוע] Shavua the world is created. The names for the days of the week, like those in the creation account, are simply the day number within the week, with Shabbat being the seventh day. Each day of the week runs from sunset to the following sunset and is figured locally. Names of weekdays The Hebrew calendar follows a seven-day weekly cycle, which runs concurrently with but independently of the monthly and annual cycles. The names for the days of the week are simply the day number within the week. In Hebrew, these names may be abbreviated using the numerical Day 1, or Yom Rishon) יום א׳ value of the Hebrew letters, for example :(( יום ראשון) "meaning "first day ,( יום א׳ abbreviated) יום ראשון – Yom Rishon .1 [corresponds to Sunday] (starting at preceding sunset of Saturday) A bronze Shabbat candlestick holder meaning "second day" made in British Mandate Palestine in the ( יום ב׳ .abbr) יום שני – Yom Sheni .2 [corresponds to Monday] 1940s. "meaning "third day ( יום ג׳ .abbr) יום שלישי – Yom Shlishi .3 [corresponds to Tuesday] [meaning "fourth day" [corresponds to Wednesday ( יום ד׳ .abbr) יום רביעי – Yom Reviʻi .4 [fifth day" [corresponds to Thursday" = ( יום ה׳ .abbr) יום חמישי – Yom Chamishi .5 [meaning "sixth day" [corresponds to Friday ( יום ו׳ .abbr) יום ששי – Yom Shishi .6 meaning "rest day" [corresponds to שבת – or more usually Shabbat ,( יום ש׳ .abbr) יום שבת – Yom Shabbat .7 Saturday] .("holy rest day") יום שבת קודש Also known as Yom Shabbat Kodesh The names of the days of the week are modeled on the seven days mentioned in the creation story.