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{{Short description|First lunar phase, the definition varies}}
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[[File: New Moon.jpg|thumb|300px|A [[computer simulation|simulated image]] of the traditionally defined new Moon: the earliest visible [[waxing crescent]] (lower right), which signals the start of a new month in many lunar and [[lunisolar calendar]]s.<ref>{{Cite web |title=New Moon |url=https://www.flickr.com/photos/24662369@N07/5837033098 |website=[[Flickr]] |date=15 June 2011 |publisher=[[NASA]]/[[Goddard Space Flight Center|GSFC]] |access-date=9 February 2020 |archive-date=4 August 2020 |archive-url=https://web.archive.org/web/20200804145330/https://www.flickr.com/photos/24662369@N07/5837033098 |url-status=live }}</ref> At new moon, mostly [[earthlight]] illuminates the [[near side of the Moon]].{{efn|[[planetshine|Planetlight]], [[zodiacal light]], and [[starlight]] contribute a negligible amount of the total light that the lunar surface reflects.}}]]
[[File:Eclipse vs new or full moons, annotated.svg|thumb|As the Earth revolves around the Sun, approximate [[axial parallelism]] of the Moon's orbital plane ([[orbital inclination|tilted]] five degrees to the [[ecliptic|Earth's orbital plane]]) results in the revolution of the [[lunar nodes]] relative to the Earth. This causes an [[eclipse season]] approximately every six months, in which a [[solar eclipse]] can occur at the new moon phase.]]

In [[astronomy]], the '''new moon''' is the first [[lunar phase]], when the [[Moon]] and [[Sun]] have the same [[ecliptic coordinate system|ecliptic longitude]].{{sfn|Meeus|1991|p=319}} At this phase, the lunar disk is not visible to the [[naked eye]], except when it is silhouetted against the Sun during a [[solar eclipse]].

The original meaning of the term 'new moon', which is still sometimes used in [[Calendar|calendrical]], non-astronomical contexts, is the first visible [[crescent]] of the Moon after [[conjunction (astronomy)|conjunction]] with the Sun.<ref>{{OED|new moon}}</ref> This thin [[wikt: waxing|waxing]] crescent is briefly and faintly visible as the Moon gets lower in the western sky after [[sunset]], with the smallest [[circular arc|arc]] angle possible around 5–7°.<ref>{{cite journal |author1=Judhistira Aria Utama<!-- xct nm --> |author2= Alif Rizza Zuhudi<!-- xct nm --> |author3= Yudi Prasetyo<!-- xct nm --> |author4= Abdul Rachman<!-- xct nm --> |author5= A. R. Sugeng Riadi<!-- xct nm --> |author6=Cep Nandi<!-- xct nm --> |author7= Lala Septem Riza<!-- xct nm --> |date=April 2025 |title=New crescent moon detection using Circular Hough Transform (CHT) |url=https://www.sciencedirect.com/science/article/abs/pii/S2213133724001173?via%3Dihub |journal=Astronomy and Computing |volume=51 |article-number=100902 |doi=10.1016/j.ascom.2024.100902|url-access=subscription}}</ref>{{rp|100902-100904}} 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 the [[Islamic calendar]]<ref>{{cite web|url=http://www.icoproject.org/icop/muh32.html |title=Visibility of Muharram Crescent 1432 AH |website=Islamic Crescents' Observation Project |archive-url=https://web.archive.org/web/20120510223714/http://icoproject.org/icop/muh32.html |archive-date=10 May 2012 |postscript=; seen on 6 December in Algeria, Iran, Saudi Arabia, South Africa.}}</ref> and in some [[lunisolar calendar]]s such as the [[Hebrew calendar]]. In the [[Chinese calendar]], the beginning of the month is marked by the last visible crescent of a [[wikt: waning|waning]] Moon.

The astronomical new moon occurs by definition at the moment of conjunction in [[Ecliptic coordinate system|ecliptical longitude]] with the Sun when the Moon is invisible from the Earth. This moment is unique and does not depend on location (because the [[ecliptic coordinate system]] is usually defined relative to the center of the Earth), and in certain circumstances, it coincides with a [[solar eclipse]].

A [[lunation]], or [[synodic month]], is the period from one new moon to the next. At the [[J2000.0]] epoch, the average length of a lunation is 29.53059 [[day]]s (or 29 days, 12 hours, 44 minutes, and 3 seconds).{{sfn|Seidelmann |1992 |p=576}} However, the length of any one synodic month can vary from 29.26 to 29.80 days (12.96 hours) due to the [[Perturbation (astronomy)|perturbing]] effects of the Sun's gravity on the Moon's [[orbital eccentricity|eccentric orbit]].<ref>{{Cite web |last=Espenak |first=Fred |title=Eclipses and the Moon's Orbit |url=http://eclipse.gsfc.nasa.gov/SEhelp/moonorbit.html |access-date=11 December 2016 |website=NASA Eclipse Web Site |publisher=NASA |archive-date=22 January 2017 |archive-url=https://web.archive.org/web/20170122075218/https://eclipse.gsfc.nasa.gov/SEhelp/moonorbit.html |url-status=live }}</ref>

==Lunation number== <!-- Note that as this article covers the religious beliefs of many different cultures, it is better to use the neutral CE/BCE notation than the explicitly Christian AD/BC notation -->
{{more citations needed section|date=December 2025|small=y}}

The ''Lunation Number'' or ''Lunation Cycle'' is a number given to each [[wiktionary: lunation|lunation]] beginning from a specific one in history. Several conventions are in use.

The most commonly used was the [[Ernest William Brown|Brown]] Lunation Number (BLN), which defines "lunation 1" as beginning at the first new moon of 1923, the year when [[Ernest William Brown|Ernest William Brown's]] [[lunar theory]] was introduced in the [[American Ephemeris and Nautical Almanac]].<ref>United States Naval Observatory. Nautical Almanac Office. (1921). Introduction. In ''The American Ephemeris and Nautical Almanac 1923'' (pp. vii)''.'' Washington Government Printing Office. </ref> Lunation 1 occurred at approximately 02:41 [[UTC]], 17 January 1923. With later refinements, the BLN was used in almanacs until 1983.<ref>{{Cite web |last1=Chapront-Touzé |first1=M |last2=Chapront |first2=J |year=2002 |title=Analytical Ephemerides of the Moon in the 20th Century |url=https://cyrano-se.obspm.fr/pub/6_documents/3_notes/lu20thcy.pdf |publisher=[[Observatoire de Paris]] |pages=21–22 }}</ref>

A more recent lunation number{{snd}} called the Lunation Number (LN){{efn|{{sic}}, not MLN}}{{snd}} was introduced by [[Jean Meeus]] in 1998,<ref>{{Cite book |last=Meeus |first=Jean |title=Astronomical algorithms |year=1998 |isbn=978-0-943396-61-3 |edition=2nd |location=Richmond, Va. |oclc=40521322 |author-link=Jean Meeus |publisher=Willmann-Bell}}</ref> and defines lunation 0 as beginning on the first new moon of 2000 (this occurred at approximately 18:14 [[UTC]], 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 by [[Herman Goldstine]],<ref>{{Cite book |last=Goldstine |first=Herman |title=New and Full Moons: 1001 B.C. to A.D. 1651 |publisher=American Philosophical Society |year=1973 |isbn=978-0-87169-094-4 |location=Philadelphia |oclc=609368 |author-link=Herman Goldstine}}</ref> 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 the [[Hebrew calendar]] with lunation 1 beginning on 6 October 3761 BCE.<ref>{{Cite web|title=Hebrew Calendar Calculator|url=https://webspace.science.uu.nl/~gent0113/hebrew/hebrewyear_year.htm|access-date=2023-02-07|website=webspace.science.uu.nl|archive-date=2022-12-07|archive-url=https://web.archive.org/web/20221207131137/https://webspace.science.uu.nl/~gent0113/hebrew/hebrewyear_year.htm|url-status=live}}</ref> It can be calculated using HLN = LN + 71234.

The Islamic Lunation Number (ILN) is the count of lunations in the [[Islamic Calendar]] with lunation 1 as beginning on the first day of the month of [[Muharram]], which occurred in 622&nbsp; CE (15 July, Julian, in the proleptic reckoning).<ref>{{Cite journal|last=Ilyas|first=M.|date=1991-06-01|title=Hijrah Day Number, Islamic Day Number and Islamic Lunation Number: New parameters for exacting the Islamic calendar|url=https://ui.adsabs.harvard.edu/abs/1991JBAA..101..175I|journal=Journal of the British Astronomical Association|volume=101|pages=175–176|bibcode=1991JBAA..101..175I|issn=0007-0297|archive-date=2022-09-20|access-date=2021-05-03|archive-url=https://web.archive.org/web/20220920032158/https://ui.adsabs.harvard.edu/abs/1991JBAA..101..175I|url-status=live}}</ref>  It can be calculated using ILN = LN + 17038.

The Thai Lunation Number (TLN) is called "มาสเกณฑ์" (Maasa-Kendha), defines lunation 0 as the beginning of [[Burmese era]] of the [[Buddhist calendar]] on Sunday, 22 March 638 CE.{{citation needed|date=April 2021}}  It can be calculated using TLN = LN + 16843.

== Lunisolar calendars ==
{{See also|Lunisolar calendar}}

===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.<ref>{{Cite web |last=Posner |first=Menachem |year=2016 |title=How Does the Spring Equinox Relate to the Timing of Passover? |url=http://www.chabad.org/holidays/passover/pesach_cdo/aid/495531/jewish/How-Does-the-Spring-Equinox-Relate-to-the-Timing-of-Passover.htm |access-date=9 December 2016 |website=Chabad |archive-date=2 January 2017 |archive-url=https://web.archive.org/web/20170102065113/http://www.chabad.org/holidays/passover/pesach_cdo/aid/495531/jewish/How-Does-the-Spring-Equinox-Relate-to-the-Timing-of-Passover.htm |url-status=live }}</ref> 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 [[Lunar theory#Babylon|handed down from Babylonians]], which is still very accurate: ca. 29.530594 days vs. a present value (see [[#Determining new moons: an approximate formula|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.{{citation needed|date=May 2015}}

===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.<ref>{{Cite web |title=A Buddhist Perspective on Fasting |url=http://www.urbandharma.org/udharma9/fasting.html |access-date=2016-09-18 |website=urbandharma.org}}</ref>

=== Hindu calendar ===
[[File: Amavasya and Prathama tithi.jpg|thumb|Amavasya and Prathama tithi]]
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]]).<ref>{{cite book |last1=Long |first1=Jeffery D. |title=Historical Dictionary of Hinduism |date=9 September 2011 |publisher=Scarecrow Press |isbn=978-0-8108-7960-7 |pages=76–77 |url=https://books.google.com/books?id=ZkkFCwAAQBAJ |language=en}}</ref><!-- next sentence suspended pending citation: 
, which is considered a powerful force for good or evil. The Hindu epic [[Mahabharatha]] states that the [[Kurukshetra War]] started this day, which was also a Tuesday (Mangalvaar, day of the week named after Mars). {{citation needed|date=May 2015}}  -->

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.<ref name="Wilhelm">{{cite book |last1=Wilhelm |first1=Ernst |title=Classical Muhurta |date=2003 |publisher=Kala Occult Publishers |isbn=978-0-9709636-2-8 |pages=23–25 |url=https://books.google.com/books?id=3zMPFJy6YygC |access-date=4 June 2022 |language=en}}</ref>
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.<ref name="Wilhelm"/>{{rp|25}}

=== [[Babylonian calendar]] ===
{{empty section|date=March 2021}}

== Lunar calendars ==
{{Main|Lunar calendar}}

===Islamic calendar===
{{see also|Solar Hijri calendar|Tabular Islamic calendar}}
The [[Islamic calendar|lunar Hijri calendar]] has exactly 12 lunar months in a year of 354 or 355 days.{{sfn|Seidelmann |1992 |pp=577}} 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 [[Ramadan (calendar month)|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. {{Citation needed|date=April 2010}} 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.<ref>{{Cite web |title=Senate body decides to draft Ruet-e-Hilal Constitution |url=http://www.pakistantoday.com.pk/2012/01/23/national/senate-body-decides-to-draft-ruet-e-hilal-constitution/ |access-date=2014-07-12 |archive-date=2014-07-14 |archive-url=https://web.archive.org/web/20140714185651/http://www.pakistantoday.com.pk/2012/01/23/national/senate-body-decides-to-draft-ruet-e-hilal-constitution/ |url-status=live }}</ref>

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.<ref>Fiqh Council of North America Decision: "[http://www.fiqhcouncil.org/Articles/IslamicLunarCalendar/tabid/169/ctl/Detail/mid/571/xmid/19/xmfid/1/Default.aspx Astronomical Calculations and Ramadan] {{Webarchive|url=https://web.archive.org/web/20100828060222/http://www.fiqhcouncil.org/Articles/IslamicLunarCalendar/tabid/169/ctl/Detail/mid/571/xmid/19/xmfid/1/Default.aspx |date=2010-08-28 }}"</ref><ref>Islamic Society of North America Decision:"[http://www.isna.com/articles/Press-Releases/RAMADAN-AND-EID-ANNOUNCEMENT.aspx Revised ISNA Ramadan and Eid Announcement] {{Webarchive|url=https://web.archive.org/web/20071111040801/http://www.isna.com/articles/Press-Releases/RAMADAN-AND-EID-ANNOUNCEMENT.aspx |date=2007-11-11 }}"</ref>

==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 [[Baháʼí Naw-Rúz|Naw-Rúz]] (Baháʼí New Year), as determined in advance by astronomical tables using [[Tehran]] as the point of reference.<ref>Momen, Moojan (2014). [http://wi.bahai.us/2014/11/29/the-badi-bahai-calendar-an-introduction The Badí` (Baháʼí) Calendar: An Introduction] {{Webarchive|url=https://web.archive.org/web/20150111210246/http://wi.bahai.us/2014/11/29/the-badi-bahai-calendar-an-introduction/ |date=2015-01-11 }}.</ref> 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.<ref name=" Clarifications">{{Cite web |last=The Universal House of Justice |date=2014-07-10 |title=To the Baháʼís of the World |url=http://universalhouseofjustice.bahai.org/activities-bahai-community/20140710_001 |access-date=2015-01-01 |archive-date=2014-07-14 |archive-url=https://web.archive.org/web/20140714233720/http://universalhouseofjustice.bahai.org/activities-bahai-community/20140710_001 |url-status=live }}</ref>

===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.{{sfn|Mosshammer|2008|p= 76|ps=: "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."}}{{sfn|Dershowitz|Reingold|2008|pp=114-115}}

== See also ==
{{Portal|Solar System}}
{{Div col|colwidth=30em}}
* {{Annotated link |Black moon}}
* [[Blue moon]]{{snd}} any one of three unconnected events: either a second [[full moon]] in a calendar [[month]], the third full moon in a [[season]] containing four, or a moon that appears [[blue]] due to atmospheric effects)
* {{Annotated link |Dark moon}}
* {{Annotated link |Hilal (crescent moon)}}
* {{Annotated link |Islamic New Year}}
* {{Annotated link |Lunar phase}}
* {{Annotated link |Solar eclipse}}
* {{Annotated link |Wet moon}}
{{Div col end}}

<!-- not included because they are not particularly 'new moons': 
* [[Blood moon (eclipse)]]
* [[Harvest moon]]
* [[Hunter's moon]] 
* [[Lilith (fictitious moon)]]
* [[Occultation#Occultations by the Moon]]
-->

== Notes ==
{{Reflist|group=note}}
{{notelist}}

== References ==
{{Reflist}}

===Works cited===
*{{Cite book |last1=Dershowitz |first1=Nachum |title-link=Calendrical Calculations|title=Calendrical Calculations |last2=Reingold |first2=Edward M. |publisher=Cambridge University Press |year=2008 |isbn=978-0-521-88540-9 |author-link=Nachum Dershowitz |author-link2=Edward Reingold}}
*{{cite book |last1=Meeus |first1=Jean |year=1991 |title=Astronomical Algorithms |publisher=Willmann-Bell |isbn=978-0-943396-35-4 |url=https://archive.org/details/astronomicalalgorithmsjeanmeeus1991}}
*{{Cite book |author-link=Alden Mosshammer|last=Mosshammer |first=Alden A. |title=The Easter Computus and the Origins of the Christian Era |publisher=Oxford University Press |year=2008 |isbn=978-0-19-954312-0}}
*{{cite book |editor1-last=Seidelmann |editor1-first=P. Kenneth |title=Explanatory Supplement to the Astronomical Almanac |date=1992 |publisher=University Science Books |isbn=978-0-935702-68-2 |url=https://archive.org/details/131123ExplanatorySupplementAstronomicalAlmanac}}

== External links ==
* [http://www.crescentmoonwatch.org/ Moon Watch site] ({{Webarchive|url=https://web.archive.org/web/20110303213524/http://www.crescentmoonwatch.org/ |date=2011-03-03 }}) of the [[HM Nautical Almanac Office|Nautical Almanac Office]]

{{The Moon}}
{{Authority control}}

{{DEFAULTSORT:New Moon}}
[[Category:New moon| ]]
[[Category:Phases of the Moon]]