Alunisolar calendar is acalendar in manycultures, that combines monthlylunar cycles with thesolar year. As with all calendars which divide the year into months, there is an additional requirement that the year have a whole number of months (Moon cycles). The majority of years have twelve months but every second or third year is anembolismic year, which adds a thirteenthintercalary, embolismic, or leap month.
In contrast to purelylunar calendars such as theIslamic calendar, lunisolar calendars have additional intercalation rules that reset them periodically into a rough agreement with the solar year and thus with the seasons.
The Five Phases and Four Seasons of the traditionalChinese lunisolar calendar, with English translation.
TheChinese calendar (華夏曆法) orChinese lunisolar calendar is also called Agricultural Calendar [農曆; 农历; Nónglì; 'farming calendar'], or Yin Calendar [陰曆; 阴历; Yīnlì; 'yin calendar']), as movements of the sun (representingYang) and moon (representing Yin) are the references for the Chinese lunisolar calendar calculations.[citation needed] The Chinese lunisolar calendar is the origin of some variant calendars adopted by other neighboring countries, such as Vietnam and Korea.
Together with astronomical, horological, andphenological observations, definitions, measurements, and predictions of years, months, and days were refined. Astronomical phenomena and calculations emphasized especially the efforts to mathematically correlate the solar and lunar cycles from the perspective of the earth,[citation needed] which however are known to require some degree of numeric approximation or compromise.
The earliest record of the Chinese lunisolar calendar was in theZhou dynasty (1050 BC – 771 BC, around 3000 years ago.[2] Throughout history, the Chinese lunisolar calendar had many variations and evolved with different dynasties with increasing accuracy, including the "six ancient calendars" in theWarring States period, the Qin calendar in theQin dynasty, the Han calendar or the Taichu calendar in theHan dynasty andTang dynasty, the Shoushi calendar in theYuan dynasty, and the Daming calendar in theMing dynasty, etc. Starting in 1912, the western solar calendar is used together with the lunisolar calendar in China.
Atropical year is approximately 365.2422days long and asynodic month is approximately 29.5306 days long,[4] so a tropical year is approximately365.2422 / 29.5306 ≈ 12.36826 months long. Because 0.36826 is between1⁄3 and1⁄2, a typical year of 12 months needs to be supplemented with one intercalary or leap month every 2 to 3 years. More precisely, 0.36826 is quite close to7⁄19 (about 0.3684211): several lunisolar calendars have 7 leap months in every cycle of 19 years (called a 'Metonic cycle'). TheBabylonians applied the 19-year cycle in the late sixth century BCE.[5]
Intercalation of leap months is frequently controlled by the "epact", which is the difference between the lunar and solar years (approximately 11 days). The classic Metonic cycle can be reproduced by assigning an initial epact value of 1 to the last year of the cycle and incrementing by 11 each year. Between the last year of one cycle and the first year of the next the increment is 12 – thesaltus lunae (Latin for 'leap of the moon') – which causes the epacts to repeat every 19 years. When the epact reaches 30 or higher, an intercalary month is added and 30 is subtracted. The Metonic cycle states that 7 of 19 years will contain an additional intercalary month and those years are numbered: 3, 6, 8, 11, 14, 17 and 19. Both the Hebrew calendar and the Julian calendar use this sequence.[citation needed]
The Buddhist and Hebrew calendars restrict the leap month to a single month of the year;[citation needed] the number of common months between leap months is, therefore, usually 36, but occasionally only 24 months. Because the Chinese and Hindu lunisolar calendars allow the leap month to occur after or before (respectively) any month but use the true apparent motion of theSun,[citation needed] their leap months do not usually occur within a couple of months ofperihelion, when the apparent speed of the Sun along theecliptic is fastest (now about 3 January). This increases the usual number of common months between leap months to roughly 34 months when a doublet of common years occurs, while reducing the number to about 29 months when only a common singleton occurs.[citation needed]
An alternative way of dealing with the fact that a solar year does not contain an integer number oflunar months is by including uncounted time in a period of the year that is not assigned to a named month.[6] SomeCoast Salish peoples used a calendar of this kind. For instance, theChehalis began their count of lunar months from the arrival of spawningchinook salmon (in Gregorian calendar October), and counted 10 months, leaving an uncounted period until the next chinooksalmon run.[7]
^The modern Hebrew calendar, since it is based on rules rather than observations, does not exactly track the tropical year, and in fact the average Hebrew year of about 365.2468 days is intermediate between the tropical year (about 365.2422 days) and the sidereal year (about 365.2564 days).
^Richards, E. G. (2013). "Calendars". In Urban, Sean; Seidelmann, P. Kenneth (eds.).Explanatory Supplement to the Astronomical Almanac (3rd ed.). Mill Valley, CA: University Science Books. pp. 583, 592, §15.4.ISBN978-1-891389-85-6.
^P. 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)
^Nilsson, Martin P. (1920), "Calendar Regulation 1. The Intercalation",Primitive Time-Reckoning: A Study in the Origins and First Development of the Art of Counting Time among the Primitive and Early Culture Peoples, Lund: C. W. K. Gleerup, p. 240,The Lower Thompson Indians in British Columbia counted up to ten or sometimes eleven months, the remainder of the year being called the autumn or late fall. This indefinite period of unnamed months enabled them to bring the lunar and solar year into harmony.
^Suttles, Wayne P.Musqueam Reference Grammar, UBC Press, 2004, p. 517.
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