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| Lunar calendar (East Asia) | |
|---|---|
| Name | Lunar calendar (East Asia) |
| Alternative names | Lunisolar calendar, Chinese calendar, East Asian calendar |
| Type | Lunisolar calendar |
| Country | China, Korea, Vietnam, Japan |
| Introduced | Ancient China |
| Epoch | Various era-based epochs (e.g., Han dynasty) |
| Current use | Traditional festivals, agriculture, astrology |
Lunar calendar (East Asia) The East Asian lunar calendar is a family of interrelated lunisolar calendars historically developed in China and transmitted to Korea, Vietnam, and Japan. It served imperial administrations such as the Han dynasty, Tang dynasty, and Ming dynasty for dating edicts, managing agriculture, and marking rituals tied to the Chinese zodiac and astronomical observatories like Shoushi Observatory.
The system originated in ancient China with contributions from figures associated with the Zhou dynasty, Han dynasty, and astronomers working under courts of Emperor Wu of Han, Emperor Gaozu of Han, and later reformers during the Tang dynasty and Song dynasty. Key implementations include the Taichu calendar and the Shoushi calendar; later adjustments were promulgated under the Yuan dynasty, Ming dynasty, and Qing dynasty. Transmission occurred via tributary and cultural contacts with the Silla kingdom, Goryeo, Joseon dynasty, and Heian period Japan, as well as Đại Việt (Vietnam) courts. European encounters from the Jesuits and scientists like Matteo Ricci and Ferdinand Verbiest influenced syncs of observational techniques in the Ming court and the Qing court.
The calendar is a lunisolar system synchronizing the synodic month with the tropical year by inserting intercalary months based on solar terms computed from the ecliptic longitude of the Sun. The traditional division into 24 solar terms (節気) links to observatories such as the Beijing Ancient Observatory and star catalogs used in the Song dynasty and Ming dynasty. Month lengths alternate to approximate the 29.53-day synodic month, with rules for leap months derived from astronomical methods advanced by astronomers like Zu Chongzhi and court mathematicians during the Tang dynasty. Epochal year counts have varied under regimes such as Han dynasty era names and later imperial reign titles like those of the Kangxi Emperor and Qianlong Emperor.
Regional adaptations reflect local astronomy and political authority: the Chinese calendar under imperial courts codified era names and intercalation; the Korean calendar was standardized in the Joseon dynasty with inputs from scholars tied to Sejong the Great and institutions like the Royal Observatory; the Vietnamese calendar (Âm lịch) adapted Chinese cycles during the Ly dynasty and Tran dynasty courts and later under Nguyen dynasty reforms; the Japanese calendar introduced Chinese models during the Asuka period and Nara period, later revised in the Meiji Restoration toward the Gregorian calendar while retaining festival dates. Each variant used local offices—e.g., the Ministry of Rites in China or the Sangjeongwon in Korea—to promulgate calendar law.
Major festivals anchored in the calendar include Chinese New Year (Spring Festival), Lantern Festival, Dragon Boat Festival, Mid-Autumn Festival, Qingming Festival, and Korean celebrations like Seollal and Chuseok, Vietnamese observances such as Tết and Japanese events that historically aligned with lunar months like Setsubun prior to modern reforms. These observances interlink with the Chinese zodiac cycle, imperial rites at venues like the Temple of Heaven, agrarian rituals referenced in Book of Odes practices, and timekeeping used by scholars in Confucian academies such as Yuelu Academy.
Contact with Western calendrical science and internal administrative needs led to reforms: Jesuit astronomers collaborated at the Ming court and Qing court and figures like Li Shizhen and Xu Guangqi were involved in astronomical modernization. Japan adopted the Gregorian calendar in the Meiji Restoration, while Vietnam and Korea shifted civil uses to the Gregorian system in the 20th century during interactions with colonial administrations such as the French colonial empire in Indochina and Japanese Empire rule over Korea. China officially adopted the Gregorian calendar (Gregorian reforms) for civil affairs in the early 20th century under the Republic of China, yet traditional lunisolar reckoning persisted for cultural scheduling.
Today the lunisolar calendars remain legally and culturally significant: civil law in jurisdictions such as the People's Republic of China, Republic of China (Taiwan), Republic of Korea, Socialist Republic of Vietnam, and Japan recognizes traditional festival dates even after civil calendars shifted to the Gregorian calendar. Governments issue official lunar-solar calendars for public holidays; religious communities, folk associations, and diaspora organizations in places like Singapore, Malaysia, Indonesia, United States, Canada, and Australia use them for planning festivals and rituals tied to temples like Temple of Literature or diaspora institutions associated with Overseas Chinese networks.
Modern computation uses algorithms based on astronomical formulas and ephemerides from institutions such as the International Astronomical Union, Jet Propulsion Laboratory, and national observatories like the Purple Mountain Observatory. Implementations appear in software libraries for Unix, Windows, Android, and iOS and standards in programming ecosystems like Python, JavaScript, and C++ via libraries referencing algorithms by researchers influenced by historical rules codified under dynasties like the Qing dynasty. Conversion involves calculating new moons from dynamical time, applying the 24 solar terms derived from ecliptic longitude, and inserting intercalary months per the traditional rule sets preserved in historical records from the Han dynasty through the Qing dynasty.