Korean calendar

Throughout its many years of history, various calendar systems have been used in Korea. Many of them were adopted from the lunar Chinese calendar system, with modifications occasionally made to accommodate Korea's geographic location and seasonal patterns.
The solar Gregorian calendar was adopted in 1896, by Gojong of Korea. Koreans now mostly use the Gregorian calendar; however, traditional holidays and age-reckoning for older generations are still based on the traditional lunisolar calendar.
During the early Goryeo period, the Tang-made Xuanming calendar (선명력; 宣明曆) was used until 1281. While the Tang revised the Xuanming calendar several times Korea insisted on using an unmodified version until Munjong's reign, when several improvised calendars, such as the Sipchŏng (십정력; 十精曆), Ch'iryo (칠요력; 七曜曆), Kyŏnhaeng (견행력; 見行曆), Tun'gap (둔갑력; 遁甲曆), and T'aeil (태일력; 太一曆) calendars were created.
In 1281 (the 7th year of Chungnyeol's reign) the Yuan-made Shòushí calendar (수시력; 授時曆) was adopted. However, Goryeo scholars tended to prefer the obsolete Xuanming calendar, which they were more accustomed to. During the late Goryeo period a revised version of Shòushí, known as the Taet'ong calendar (대통력; 大統曆) saw limited use.
Shòushí continued as the standard calendar until early Joseon when the Ch'ilchŏngsan (칠정산; 七政算) was created to serve as the first Korea-specialized calendar system during the reign of Sejong the Great. The Ch'ilchŏngsan consisted of two books, the Ch'ilchŏngsannaep'yŏn (칠정산내편; 七政算內篇) which detailed methods to accurately calculate dates and celestial movements regarding Korea's geographic location based on the Shòushí calendar, and the Ch'ilchŏngsanoep'yŏn (칠정산외편;七政算 外篇), which was based on the Huihui Lifa.
Beginning in 1644 (22nd year of Injo's reign), Korean scholars began discussing the adaptation of the Qing-made Shixian calendar (시헌력; 時憲暦; siheollyeok), as the limitations of the Ch'ilchŏngsan became clear. Although the Shixian calendar was officially adopted in 1653 (4th year of Hyojong's reign), it was not implemented in earnest until 1725 (1st year of Yeongjo's reign) as Korean scholars had little knowledge of western astronomy (which heavily influenced the Shixian calendar) and the Qing were reluctant to reveal any information of their new innovation.
The traditional calendar designated its years via Korean era names from 270 to 963, then Chinese era names with Korean era names at a few times until 1894. In 1894 and 1895, the lunar calendar was used with years numbered from the foundation of the Joseon Dynasty in 1392.
The Gregorian calendar was adopted on 1 January 1896, with the Korean era name Geonyang (건양; 建陽; lit. 'adopting solar calendar').
From 1945 until 1961 in South Korea, the Dangun calendar was used, where Gregorian calendar years were counted from the foundation of Gojoseon in 2333 BC (regarded as year one), the date of the legendary founding of Korea by Dangun. These Dangi (단기; 檀紀) years were 4278 to 4294. This numbering was informally used with the Korean lunar calendar before 1945 but has only been occasionally used since 1961, and mostly in North Korea prior to 1997.
Although not being an official calendar, in South Korea, the traditional Korean calendar is still maintained by the government. The current version is based on the Shixian calendar, which was in turn revised by Jesuit scholars.
In North Korea, the Juche calendar was used between 1997 and 2024 to number its years, based on the birth of the state's founder Kim Il Sung.
Note that traditional Korean calendar has no concept of weekdays: the following are names of weekdays in the modern (Western) calendar.
In modern Korean language, the months of both the traditional lunisolar and Western calendars are named by prefixing Sino-Korean numerals to wol, the Sino-Korean word for "month". Traditionally, when speaking of individuals' birth months, the months of the lunisolar calendar were named by prefixing the native Korean name of the animal associated with each Earthly Branch in the Chinese zodiac to dal, the native Korean word for "month". Additionally, the first, eleventh, and twelfth months have other Korean names which are similar to traditional Chinese month names. However, the other traditional Chinese month names, such as Xìngyuè ("apricot month") for the second month, are not used in Korean.
The lunar calendar is used for the observation of traditional festivals, such as Seollal, Chuseok, and Buddha's Birthday. It is also used for jesa memorial services for ancestors and the marking of birthdays by older Koreans.
There are also many regional festivals celebrated according to the lunar calendar.