A lunar calendar or lunar calendar is only at the maturity of the moon -based calendar . To distinguish it from a lunisolar calendar , in which a rough adjustment to the solar year is made with the help of an occasional leap month , it is also called a free lunar calendar or unbound lunar calendar .
In it, twelve lunar months are combined into a lunar year (lunar year), which is about 11 days shorter than a solar year in a solar calendar .
History and application
Lunar calendars are older than solar calendars because they are based on a clearly observable celestial phenomenon, namely the phases of the moon . The solar phases, for example the equinoxes or the solstices , are much more difficult to determine.
The period of the moon phases is the synodic month ( lunation ) with an average length of 29.53059 days (fluctuation between about 29.27 and 29.83 days). In the calendar, 6 months with 29 days and 6 months with 30 days are used alternately. The lunar calendar year is 354 days long (6 · 29 + 6 · 30). To adapt to the astronomically exact length of a lunar year with 354.3671 days (12 lunations), the lunar calendar year is about one day longer every three years. There is no switching rule of any kind , it is superfluous because the beginning of each lunar month results from observation, not a calculation.
As a rule, the easily identifiable day of the new light , which was previously observed and announced by a person of authority, is used as the beginning of the month . The possibility of calculating this date in advance (so-called arithmetic or cyclical date) makes it independent of arbitrariness and possible cloudiness. The new year begins every twelve months.
An example of a lunar calendar still used today - at least for religious purposes - is the Islamic calendar . Ramadan , the month of fasting, is the most important annual religious event in Islam. Like all Islamic calendar dates, it slides backwards once every 34 years through a solar year of a solar calendar.
A person whose age according to Islamic tradition is given as 34 years is only 33 solar years old. 100 solar years correspond to about 103 lunar years. The lunar calendar is the more advanced the longer the years are counted.
The reuse of the lunar calendar was prescribed by the Prophet Mohammed in the 7th century, i.e. at a time when a lunisolar calendar ( Jewish calendar ) and a solar calendar ( Julian calendar ) were already in use in his area ( Arabian Peninsula ) .
In Iran, the age of majority is calculated according to the lunar years.
- LE Dogett: Calendars . In: P. Kenneth Seidelmann (Ed.): Explanatory Supplement to the Astronomical Almanac . University Science Books, Sausalito CA. ( english )