Editing Lunar calendar

{{Short description|Calendar based only on the Moon}}
{{redirects|Lunar date|uses not on Earth|timekeeping on the Moon}}
[[File:2025_Lunar_Calendar.png|thumb|upright 1.5|Lunar calendar year 2025]]
A '''lunar calendar''' is a [[calendar]] based on the [[month]]ly cycles of the [[Moon]]'s [[lunar phase|phase]]s ([[Lunar month#Synodic month|synodic month]]s, [[lunation]]s), in contrast to [[solar calendar]]s, whose annual cycles are based on the [[solar year]], and [[lunisolar calendar]]s, whose [[lunar month]]s are brought into alignment with the solar year through some process of [[intercalation (timekeeping)|intercalation]]{{snd}}such as by insertion of a [[leap month]]. The most widely observed lunar calendar is the [[Islamic calendar]].{{efn|Iran operates [[Solar Hijri calendar]], which is purely solar.}} The details of when months begin vary from calendar to calendar, with some using [[new moon|new]], [[full moon|full]], or [[crescent]] moons and others employing detailed calculations.

Since each lunation is approximately {{frac|29|1|2}}&nbsp;days,<ref name=ESAA>{{cite book | title=Explanatory Supplement to the Astronomical Almanac |year=1992 | editor=P. Kenneth Seidelmann |page=577 |url=https://archive.org/details/131123ExplanatorySupplementAstronomicalAlmanac/page/n302/mode/1up | quote=For convenience, it is common to speak of a lunar year of twelve synodic months, or 354.36707 days.}} (which gives a mean synodic month as 29.53059 days or 29 days 12 hours 44 minutes and 3 seconds)</ref> it is common for the months of a lunar calendar to alternate between 29 and 30&nbsp;days. Since the period of 12 such lunations, a '''lunar year''', is 354&nbsp;days, 8&nbsp;hours, 48&nbsp;minutes, 34&nbsp;seconds (354.36707&nbsp;days),<ref name=ESAA /> lunar calendars are 11 to 12 days shorter than the [[tropical year|solar year]]. In lunar calendars, which do not make use of lunisolar calendars' intercalation, the lunar months cycle through all the seasons of a solar year over the course of a 33–34 lunar-year cycle (see, e.g., [[list of Islamic years]]).

==History==
Scholars have argued that ancient hunters conducted regular astronomical observations of the Moon back in the [[Upper Paleolithic|Upper Palaeolithic]].<ref>{{Cite journal|last=Gurshtein|first=Alex|date=2005-01-01|title=Did the Pre-Indo-Europeans Influence the Formation of the Western Zodiac?|url=https://www.researchgate.net/publication/280531206|journal=Journal of Indo-European Studies |volume=33|pages=106}}</ref> Samuel L. Macey dates the earliest uses of the Moon as a time-measuring device back to 28,000–30,000 years ago.<ref>{{Cite book|url=https://books.google.com/books?id=F7wNQk219KMC|title=Encyclopedia of Time|last=Macey|first=Samuel L.|date=1994|publisher=Taylor & Francis|isbn=9780815306153|pages=75|language=en}}</ref>

== Start of the lunar month ==
Lunar and lunisolar calendars differ as to which day is the first day of the month. Some are based on the first sighting of the [[lunar phase|lunar crescent]], such as the [[Islamic calendar|Hijri calendar]] observed by most of Islam. Alternatively, in some lunisolar calendars, such as the [[Hebrew calendar]] and [[Chinese calendar]], the first day of a month is the day when an astronomical [[new moon]] occurs in a particular time zone. In others, such as some [[Hindu calendar]]s, each month begins on the day after the full moon.

== Length of the lunar month ==
The length of each lunar cycle varies slightly from the average value. In addition, observations are subject to uncertainty and weather conditions. Thus, to minimise uncertainty, there have been attempts to create fixed arithmetical rules to determine the start of each calendar month. The best known of these is the [[Tabular Islamic calendar]]: in brief, it has a 30-year cycle with 11 [[leap year]]s of 355 days and 19 years of 354 days. In the long term, it is accurate to one day in about 2,500 solar years or 2,570 lunar years. It also deviates from observation by up to about one or two days in the short term. The algorithm was introduced by Muslim astronomers in the 8th century to predict the approximate date of the first crescent moon, which is used to determine the first day of each month in the [[Islamic calendar|Islamic lunar calendar]].<ref>{{cite web |title=The Arithmetical or Tabular Islamic Calendar |publisher=Mathematical Institute, [[Utrecht University]] |first=R. H. |last=van Gent |date=October 2023 |access-date=4 January 2024 |url=https://webspace.science.uu.nl/~gent0113/islam/islam_tabcal.htm}}</ref>

== List of lunar calendars <span class="anchor" id="List of lunar calendars"></span> <!-- [[List of lunar calendars]] redirects here -->==
<!-- Celtic calendar was lunisolar -->
<!-- Chinese calendar is lunisolar -->
<!-- [[Gezer calendar|Gezer Calendar]] page does not support being lunar -->
<!-- [[Igbo calendar]] lunisolar -->
* [[Islamic calendar|Islamic Hijri calendar]]{{efn|Calendar used by the large majority of Muslims outside Iran}}
* [[Javanese calendar]]{{efn|After 1633 CE reform}}

== See also ==
{{Portal|Solar System}}
* [[List of calendars]]
* [[Islamic calendar]]
* [[Lunisolar calendar]]
* [[Lunar phase]]
* [[Epact]]
* [[Paschal Full Moon]]

==Notes==
{{Notelist}}

== References ==
{{Reflist|30em}}

== External links ==
{{calendars}}
{{Time measurement and standards}}
{{Chronology}}
{{The Moon}}
{{Prehistoric technology|state=collapsed}}
{{Authority control}}

{{DEFAULTSORT:Lunar Calendar}}
[[Category:Lunar calendars| ]]