The original meaning of the term 'new moon', which is still sometimes used incalendrical, non-astronomical contexts, is the first visiblecrescent of the Moon afterconjunction with the Sun.[3] This thinwaxing crescent is briefly and faintly visible as the Moon gets lower in the western sky aftersunset. The precise time and even the date of the appearance of the new moon by this definition will be influenced by the geographical location of the observer. The first crescent marks the beginning of the month in theIslamic calendar[4] and in somelunisolar calendars such as theHebrew calendar. In theChinese calendar, the beginning of the month is marked by the last visible crescent of awaning Moon.
The astronomical new moon occurs by definition at the moment of conjunction inecliptical longitude with the Sun when the Moon is invisible from the Earth. This moment is unique and does not depend on location, and in certain circumstances, it coincides with asolar eclipse.
Alunation, orsynodic month, is the period from one new moon to the next. At theJ2000.0 epoch, the average length of a lunation is 29.53059days (or 29 days, 12 hours, 44 minutes, and 3 seconds).[5] However, the length of any one synodic month can vary from 29.26 to 29.80 days (12.96 hours) due to theperturbing effects of the Sun's gravity on the Moon'seccentric orbit.[6]
A more recent lunation number – called the Lunation Number (LN)[b] – was introduced byJean Meeus in 1998,[8] and defines lunation 0 as beginning on the first new moon of 2000 (this occurred at approximately 18:14UTC, 6 January 2000). The formula relating Meeus's Lunation Number to the Brown Lunation Number is BLN = LN + 953.
The Goldstine Lunation Number (GLN) refers to the lunation numbering used byHerman Goldstine,[9] with lunation 0 beginning on 11 January 1001 BCE, and can be calculated using GLN = LN + 37105.
The Hebrew Lunation Number (HLN) is the count of lunations in theHebrew calendar with lunation 1 beginning on 6 October 3761 BCE.[10] It can be calculated using HLN = LN + 71234.
The Islamic Lunation Number (ILN) is the count of lunations in theIslamic Calendar with lunation 1 as beginning on the first day of the month ofMuharram, which occurred in 622 CE (15 July, Julian, in the proleptic reckoning).[11] It can be calculated using ILN = LN + 17038.
The Thai Lunation Number (TLN) is called "มาสเกณฑ์" (Maasa-Kendha), defines lunation 0 as the beginning ofBurmese era of theBuddhist calendar on Sunday, 22 March 638 CE.[citation needed] It can be calculated using TLN = LN + 16843.
The new moon, in HebrewRosh Chodesh, signifies the start of every Hebrew month and is considered an important date and minor holiday in theHebrew calendar. The modern form of the calendar practiced in Judaism is a rule-basedlunisolar calendar, akin to theChinese calendar, measuring months defined in lunar cycles as well as years measured in solar cycles, and distinct from the purely lunarIslamic calendar and the predominantly solarGregorian calendar. The Jewish months are fixed to the annual seasons by setting the new moon ofAviv, thebarley ripening, orspring, as the first moon and head of the year.[12] Since theBabylonian captivity, this month is calledNisan, 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.[13] This fixed lunisolar calendar follows rules introduced byHillel II and refined until the ninth century. This calculation makes use of a mean lunation length used byPtolemy andhanded down from Babylonians, which is still very accurate: ca. 29.530594 days vs. a present value (seebelow) 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.[citation needed]
The new moon is the beginning of the month in theChinese calendar. Some Buddhist Chinese keep a vegetarian diet on the new moon and full moon each month.[14]
The new moon is significant in the lunarHindu calendar. The first day of the calendar starts the day after the dark moon phase (Amavasya).[15]
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.[16]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.[16]: 25
Thelunar Hijri calendar has exactly 12 lunar months in a year of 354 or 355 days.[17] 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 themonth of Ramadan will begin is not known in advance). InSaudi Arabia, the new King Abdullah Centre for Crescent Observations and Astronomy in Mecca has a clock for addressing this as an international scientific project.[citation needed] InPakistan, there is a "Central Ruet-e-Hilal Committee" whose head is Mufti Muneeb-ur-Rehman, assisted by 150 observatories of thePakistan Meteorological Department, which announces the sighting of the new moon.[18]
An attempt to unify Muslims on a scientifically calculated worldwide calendar was adopted by both theFiqh Council of North America and theEuropean 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.[19][20]
TheBaháʼí calendar is a solar calendar with certain new moons observed asmoveable feasts.In theBaháʼí Faith, effective from 2015 onwards, the "Twin Holy Birthdays", refer to two successive holy days in theBaháʼí calendar (the birth of theBáb and thebirth of Bahá'u'lláh), will be observed on the first and the second day following the occurrence of the eighth new moon afterNaw-Rúz (Baháʼí New Year), as determined in advance by astronomical tables usingTehran as the point of reference.[21] 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.[22]
^Mosshammer 2008, p. 76: "Theoretically, the epact 30=0 represents the new moon in conjunction with the sun. The epact of 1 represents the theoretical first visibility of the moon's first crescent. It is from that point as day one that the fourteenth day of the moon is counted."
![[icon]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aWiki_letter_w_cropped.svg)
