A lunar calendar is a

calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A calendar date, date is the designation of a single and specific day within such a system. A calendar is ...

based on the

month A month is a unit of time, used with calendars, that is approximately as long as a natural phase cycle of the Moon; the words ''month'' and ''Moon'' are cognates. The traditional concept of months arose with the cycle of Moon phases; such lunar mo ...

ly cycles of the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform *Phase space, a mathematica ...

s (

synodic month In lunar calendars, a lunar month is the time between two successive Syzygy (astronomy), syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Variations In Shona people, S ...

lunation In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Variations In Shona, Middle Eastern, and Euro ...

s), in contrast to

solar calendar A solar calendar is a calendar whose dates indicates the season or almost equivalently the apparent position of the Sun relative to the stars. The Gregorian calendar, widely accepted as a standard in the world, is an example of a solar calendar ...

s, whose annual cycles are based on the

solar year A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky – as viewed from the Earth or another celestial body of the Solar System – thus completing a full cycle of astronom ...

, and

lunisolar calendar A lunisolar calendar is a calendar in many cultures, that combines monthly lunar cycles with the solar year. As with all calendars which divide the year into months, there is an additional requirement that the year have a whole number of mont ...

s, whose

lunar month In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Variations In Shona, Middle Eastern, and Euro ...

s are brought into alignment with the solar year through some process of intercalationsuch as by insertion of a leap month. The most widely observed lunar calendar is the

Islamic calendar The Hijri calendar (), also known in English as the Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to determine the proper days of Islamic holidays and rituals, such as the Ramad ...

. The details of when months begin vary from calendar to calendar, with some using new, full, or

crescent A crescent shape (, ) is a symbol or emblem used to represent the lunar phase (as it appears in the northern hemisphere) in the first quarter (the "sickle moon"), or by extension a symbol representing the Moon itself. In Hindu iconography, Hind ...

moons and others employing detailed calculations. Since each lunation is approximately days, (which gives a mean synodic month as 29.53059 days or 29 days 12 hours 44 minutes and 3 seconds) it is common for the months of a lunar calendar to alternate between 29 and 30 days. Since the period of 12 such lunations, a lunar year, is 354 days, 8 hours, 48 minutes, 34 seconds (354.36707 days), lunar calendars are 11 to 12 days shorter than the

. 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 Palaeolithic The Upper Paleolithic (or Upper Palaeolithic) is the third and last subdivision of the Paleolithic or Old Stone Age. Very broadly, it dates to between 50,000 and 12,000 years ago (the beginning of the Holocene), according to some theories ...

. Samuel L. Macey dates the earliest uses of the Moon as a time-measuring device back to 28,000–30,000 years ago.

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 crescent, such as the Hijri calendar observed by most of Islam. Alternatively, in some lunisolar calendars, such as the

Hebrew calendar The Hebrew calendar (), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance and as an official calendar of Israel. It determines the dates of Jewish holidays and other rituals, such as '' yahrze ...

and

Chinese calendar The traditional Chinese calendar, dating back to the Han dynasty, is a lunisolar calendar that blends solar, lunar, and other cycles for social and agricultural purposes. While modern China primarily uses the Gregorian calendar for officia ...

, the first day of a month is the day when an astronomical

new moon In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. 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. ...

occurs in a particular time zone. In others, such as some

Hindu calendar The Hindu calendar, also called Panchangam, Panchanga (), is one of various lunisolar calendars that are traditionally used in the Indian subcontinent and Southeast Asia, with further regional variations for social and Hindu religious purposes ...

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 A leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) compared to a common year. The 366th day (or 13th month) is added to keep t ...

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 lunar calendar.

List of lunar calendars

* Islamic Hijri calendar *

Javanese calendar The Javanese calendar () is the calendar of the Javanese people. It is used concurrently with two other calendars, the Gregorian calendar and the Islamic calendar. The Gregorian calendar is the official calendar of the Republic of Indonesia and c ...

Lunisolar calendars

Most calendars referred to as "lunar" calendars are

s. Their months are based on observations of the lunar cycle, with periodic intercalation being used to restore them into general agreement with the solar year. The solar " civic calendar" that was used in

ancient Egypt Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...

showed 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 the Chinese,

Korean Korean may refer to: People and culture * Koreans, people from the Korean peninsula or of Korean descent * Korean culture * Korean language **Korean alphabet, known as Hangul or Korean **Korean dialects **See also: North–South differences in t ...

, Vietnamese,

Hindu Hindus (; ; also known as Sanātanīs) are people who religiously adhere to Hinduism, also known by its endonym Sanātana Dharma. Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pp. 35–37 Historically, the term has also be ...

Hebrew Hebrew (; ''ʿÎbrit'') is a Northwest Semitic languages, Northwest Semitic language within the Afroasiatic languages, Afroasiatic language family. A regional dialect of the Canaanite languages, it was natively spoken by the Israelites and ...

and Thai calendars. 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 the

Banks Islands The Banks Islands (in Bislama ''Bankis'') are a group of islands in northern Vanuatu. Together with the Torres Islands to their northwest, they make up the northernmost province of Torba Province, Torba. The island group lies about north of Maew ...

, which includes three months in which the edible palolo worms mass 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.R.H.Codrington. The Melanesians: Their anthropology and folklore (1891) Oxford, Clarendon Press

Notes

References

External links

{{DEFAULTSORT:Lunar Calendar