Korean calendar

The traditional Korean calendar or Dangun calendar () is a lunisolar calendar. Like most traditional calendars of other East Asian countries, the Korean Calendar is mainly derived from the Chinese calendar. Dates are calculated from Korea's meridian (135th meridian east in modern time for South Korea), and observances and festivals are based in Korean culture.
Koreans mostly use the Gregorian calendar, which was officially adopted in 1896. However, traditional holidays and age-reckoning for older generations are still based on the old calendar. The biggest festivals in Korea today, which are also national holidays, are Seollal, the first day of the traditional Korean New Year, and Chuseok its harvest moon festival. Other important festivals include Daeboreum also referred to as "Boreumdaal" (the first full moon), Dano (spring festival) and Samjinnal (spring-opening festival). Other minor festivals include Yudu (summer festival), and Chilseok (monsoon festival).
History.
The Korean calendar is derived from the Chinese calendar. The traditional calendar designated its years via Korean era names from 270 to 963, then Chinese era names with Korean era names were used 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 Korean era name ""Geon-yang" (건양 / Hanja: 建陽, "adopting solar calendar")."
From 1945 until 1961 in South Korea, 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, hence these Dangi (단기 / Hanja: 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 China's Shixian calendar (""shi-heon-nyeok" 시헌력 (時憲暦)" in Korean), which was in turn developed by Jesuit scholars. However, because the Korean calendar is now based on the moon's shape seen from Korea, occasionally the calendar diverges from the traditional Chinese calendar by one day, even though the underlying rule is the same. As a result, sometime the New Year's Day differ by one between the two countries, which last happened in 1997.
In North Korea, the Juche calendar has been used since 1997 to number its years, based on the birth of the state's founder Kim Il-sung.
Weekdays.
Note that traditional Korean calendar has no concept of "weekdays": the following are names of weekdays in the modern (Western) calendar.
Months.
In modern Korean language, the months of both the traditional lunisolar and Western calendars are named by prefixing Sino-Korean numerals to , 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 , 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.
Festivals.
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.
Traditional holidays.
There are also many regional festivals celebrated according to the lunar calendar.