New moon

Hebrew calendar The new moon, in Hebrew Rosh Chodesh, signifies the start of every Hebrew month and is considered an important date and minor holiday in the Hebrew calendar. The modern form of the calendar practiced in Judaism is a rule-based lunisolar calendar, akin to the Chinese calendar, measuring months defined in lunar cycles as well as years measured in solar cycles, and distinct from the purely lunar Islamic calendar and the predominantly solar Gregorian calendar. The Jewish months are fixed to the annual seasons by setting the new moon of Aviv, the barley ripening, or spring, as the first moon and head of the year. Since the Babylonian captivity, this month is called Nisan, and it is calculated based on mathematical rules designed to ensure that festivals are observed in their traditional season. Passover always falls in the springtime. This fixed lunisolar calendar follows rules introduced by Hillel II and refined until the ninth century. This calculation makes use of a mean lunation length used by Ptolemy and handed down from Babylonians, which is still very accurate: ca. 29.530594 days vs. a present value (see below) of 29.530589 days. This difference of only 0.000005, or five millionths of a day, adds up to about only four hours since Babylonian times. Chinese calendar The new moon is the beginning of the month in the Chinese calendar. Some Buddhist Chinese keep a vegetarian diet on the new moon and full moon each month. Hindu calendar The new moon is significant in the lunar Hindu calendar. The first day of the calendar starts the day after the dark moon phase (Amavasya). There are fifteen moon dates for each of the waxing and waning periods. These fifteen dates are divided evenly into five categories: Nanda, Bhadra', Jaya, Rikta, and Purna, which are cycled through in that order. Nanda dates are considered to be favorable for auspicious works; Bhadra dates for works related to community, social, family, and friends; and Jaya dates for dealing with conflict. Rikta dates are considered beneficial only for works related to cruelty. Purna dates are considered to be favorable for all work. === Babylonian calendar === == Lunar calendars ==

Islamic calendar The lunar Hijri calendar has exactly 12 lunar months in a year of 354 or 355 days. It has retained an observational definition of the new moon, marking the new month when the first crescent moon is seen, and making it impossible to be certain in advance of when a specific month will begin (in particular, the exact date on which the month of Ramadan will begin is not known in advance). In Saudi Arabia, the new King Abdullah Centre for Crescent Observations and Astronomy in Mecca has a clock for addressing this as an international scientific project. In Pakistan, there is a "Central Ruet-e-Hilal Committee" whose head is Mufti Muneeb-ur-Rehman, assisted by 150 observatories of the Pakistan Meteorological Department, which announces the sighting of the new moon. An attempt to unify Muslims on a scientifically calculated worldwide calendar was adopted by both the Fiqh Council of North America and the European Council for Fatwa and Research in 2007. The new calculation requires that conjunction must occur before sunset in Mecca, Saudi Arabia, and that, on the same evening, the moonset must take place after sunset. These can be precisely calculated and therefore a unified calendar is possible should it become adopted worldwide. ==Solar calendars holding moveable feasts==

Baháʼí calendar The Baháʼí calendar is a solar calendar with certain new moons observed as moveable feasts. In the Baháʼí Faith, effective from 2015 onwards, the "Twin Holy Birthdays", refer to two successive holy days in the Baháʼí calendar (the birth of the Báb and the birth of Bahá'u'lláh), will be observed on the first and the second day following the occurrence of the eighth new moon after Naw-Rúz (Baháʼí New Year), as determined in advance by astronomical tables using Tehran as the point of reference. This will result in the observance of the Twin Birthdays moving, year to year, from mid-October to mid-November according to the Gregorian calendar. Christian liturgical calendar Easter, the most important feast in the Christian liturgical calendar, is a movable feast. The date of Easter is determined by reference to the ecclesiastical full moon, which, being historically difficult to determine with precision, is defined as being fourteen days after the (first crescent) new moon. == See also ==