Alunar calendaris acalendarbased on themonthlycycles of theMoon'sphases(synodic months,lunations), in contrast tosolar calendars,whose annual cycles are based on thesolar year.The most widely observed purely lunar calendar is theIslamic calendar.[a]A purely lunar calendar is distinguished from alunisolar calendar,whoselunar monthsare brought into alignment with the solar year through some process ofintercalation– such as by insertion of aleap month.The details of when months begin vary from calendar to calendar, with some usingnew,full,orcrescentmoons and others employing detailed calculations.
Since each lunation is approximately29+1⁄2days,[1]it is common for the months of a lunar calendar to alternate between 29 and 30 days. Since the period of 12 such lunations, alunar year,is 354 days, 8 hours, 48 minutes, 34 seconds (354.36707 days),[1]purely lunar calendars are 11 to 12 days shorter than thesolar year.In purely lunar calendars, which do not make use of 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
editA lunisolar calendar was found atWarren FieldinScotlandand has been dated toc. 8000 BC,during theMesolithic period.[2][3]Some scholars argue for lunar calendars still earlier—Rappenglückin the marks on ac. 17,000year-oldcave paintingatLascauxandMarshackin the marks on ac. 27,000year-old bone baton—but their findings remain controversial.[4][5]Scholars have argued that ancient hunters conducted regular astronomical observations of the Moon back in theUpper Palaeolithic.[6]Samuel L. Macey dates the earliest uses of the Moon as a time-measuring device back to 28,000–30,000 years ago.[7]
Start of the lunar month
editLunar and lunisolar calendars differ as to which day is the first day of the month. Some are based on the first sighting of thelunar crescent,such as the Hijri calendar observed by most of Islam. Alternatively, in some lunisolar calendars, such as theHebrew calendarandChinese calendar,the first day of a month is the day when an astronomicalnew moonoccurs in a particular time zone. In others, such as someHindu calendars,each month begins on the day after the full moon.
Length of the lunar month
editThe 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 theTabular Islamic calendar:in brief, it has a 30-year cycle with 11leap yearsof 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 theIslamic lunar calendar.[8]
List of lunar calendars
editLunisolar calendars
editMost calendars referred to as "lunar" calendars are in factlunisolar calendars.Their months are based on observations of the lunar cycle, with periodicintercalationbeing used to restore them into general agreement with the solar year. The solar "civic calendar"that was used inancient Egyptshowed traces of its origin in the earlier lunar calendar, which continued to be used alongside it for religious and agricultural purposes. Present-day lunisolar calendars include theChinese,Korean,Vietnamese,Hindu,HebrewandThaicalendars.
The most common form of intercalation is to add an additional month every second or third year. Some lunisolar calendars are also calibrated by annual natural events which are affected by lunar cycles as well as the solar cycle. An example of this is the lunisolar calendar of theBanks Islands,which includes three months in which the ediblepalolo wormsmass on the beaches. These events occur at the last quarter of the lunar month, as the reproductive cycle of the palolos is synchronized with the moon.[9]
See also
edit
Notes
edit- ^Iran operatesSolar Hijri calendar,which is purely solar.
- ^Calendar used by the large majority of Muslims outside Iran
References
edit- ^abP. Kenneth Seidelmann, ed. (1992).Explanatory Supplement to the Astronomical Almanac.p. 577.
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) - ^Nancy Owano,Scotland lunar-calendar find sparks Stone Age rethink,Phys.org, 27 July 2013Archived9 August 2013 at theWayback Machine
- ^Gaffney, V.; et al. (2013)."Time and a Place: A luni-solar 'time-reckoner' from 8th millennium BC Scotland".Internet Archaeology(34).doi:10.11141/ia.34.1.Archivedfrom the original on 18 July 2013.Retrieved16 July2013.
In doing so the monument anticipates problems associated with simple lunar calendars by providing an annual astronomic correction in order to maintain the link between the passage of time indicated by the Moon, the asynchronous solar year, and the associated seasons.
- ^James Elkins,Our beautiful, dry, and distant texts(1998) 63ff.
- ^"Oldest lunar calendar identified".BBC News.2000-10-16.Retrieved2013-03-14.
- ^Gurshtein, Alex (2005-01-01)."Did the Pre-Indo-Europeans Influence the Formation of the Western Zodiac?".Journal of Indo-European Studies.33:106.
- ^Macey, Samuel L. (1994).Encyclopedia of Time.Taylor & Francis. p. 75.ISBN9780815306153.
- ^van Gent, R. H. (October 2023)."The Arithmetical or Tabular Islamic Calendar".Mathematical Institute,Utrecht University.Retrieved4 January2024.
- ^R.H.Codrington. The Melanesians: Their anthropology and folklore (1891) Oxford, Clarendon Press