National Foundation Day (Korea)

Gaecheonjeol (Korean: 개천절; Hanja: 開天節; lit. 'The day the heaven opened') is a public holiday in South Korea on 3 October. Also known by the English name National Foundation Day, this holiday celebrates the legendary formation of the first Korean state of Gojoseon by legendary king Dangun in 2333 BC. This date has traditionally been regarded by Koreans as the date for the founding of the Korean race.
Gaecheonjeol is also recognized in North Korea, although not as a public holiday, with an annual ceremony at the Mausoleum of Tangun, the founder of Gojoseon.
Gae-cheon ('Opening of Heaven') refers to 3 October 2457 BCE, the date when Hwanung (환웅) descended from heaven to live with mankind.
The harvest ceremony was celebrated in the Korean realms; Yeonggo (영고; 迎鼓) of Buyeo; Mucheon (무천; 舞天) of Yemaek; Gyeeum (계음; 契飮) of Mahan and Byeonhan; Dongmaeng (동맹; 東盟) of Goguryeo; and Palgwanhoe (팔관회; 八關會) of Silla.
In 1909, Gaecheonjeol was established as a national holiday. At first, the holiday was observed on the third day of the 10th month on the lunar calendar, but it has been fixed on 3 October of the solar Gregorian calendar since 1949.
On 15 January 1909, when Daejongism reopened its gate with Nachul at the center, it was established as a celebration day and celebrated every year. Events like this contributed to fostering the spirit of the Korean people under the pressure of Japanese colonial rule.
When the Provisional Government of the Republic of Korea was established in 1919, the provisional government established 3 October of the lunar calendar as a national holiday. This is based on the universal perception of history, which saw Dangun as the founder of the Hankyoreh at the time and Gojoseon as the first nation of the Korean people.
Following the establishment of the Republic of Korea after Korea's liberation from Japanese colonial rule, the Dangungiwon (단군기원; 檀君紀元), or dan-gi (단기; 檀紀), was enacted as the official calendar of the nation in the "Act on official calendars" on 25 September 1948. On 1 October 1949, the "Act on National Day of celebration" was enacted and the date of the third lunar month was designated as the Gaecheonjeol. Since it was originally a lunar calendar, it had been used as a lunar calendar even after the establishment of the Korean government, but after the deliberation of the "Deliberation Council regarding the change of celebrations of gaecheonjeol from the lunar calendar to the solar calendar," which was appointed by the Culture and Education Ministry in 1949, it changed the lunar calendar into a solar calendar and became a great practice as it was said that the records of 3 October were precious.
On the other hand, Daejongism believes that the original meaning of the word "Gaecheon" is not Dangun's founding day, but the third day of the lunar month of October 2457 BC, when Hwanung opened the sky gate and came down below Sin Dansu, Taebaek Mountain, and began the great work of Hongikingan (弘益人間, translated as 'to widely benefit the humans') and Yihwasegye (理化世界, translated as 'ruling the word with reason').
The song was originally sung by people who were believers of Daejongism. After the National Foundation Day becomes as a national holiday, the lyrics were changed as it is sung nowadays.
The lyrics are as follows.
Gaecheonjeol is a public holiday in South and North Korea on 3 October. Also known by the English name National Foundation Day, this holiday celebrates the legendary formation of the first Korean state of Gojoseon in 2333 BC. This date has traditionally been regarded as the date for the founding of the Korean people. Although not as a public holiday, with an annual ceremony at the Mausoleum of Tangun, the founder of Gojoseon. The word “개천절” has a specific meaning which widely benefits humans and ruling the world with reason. National holidays can be defined as those commemorations that a nation's government has deemed important enough to warrant inclusion in the list of official public holidays. They tend to honor a person or event that has been critical in the development of the nation and its identity. Such people and events usually reflect values and traditions shared by a large portion of the citizenry.
When the Provisional Government of the Republic of Korea was established in 1919, the provisional government established 3 October of the lunar calendar as a national holiday. After the deliberation of the "Deliberation Council regarding the change of celebrations of gaecheonjeol (개천절) from the lunar calendar to the solar calendar," which was appointed by the Culture and Education Ministry in 1949, it changed the lunar calendar into a solar calendar and became a great practice as it was said that the records of 3 October were precious. There is also a song that was originally sung by people who were believers of Daejongism. After National Foundation Day became a national holiday, the lyrics were changed as it is sung nowadays. Also, the holiday is similar to many holidays around the world in that it is celebrated with huge displays of fireworks. In Seoul, it always takes place in Yeouido Han River Park, and crowds of people will gather there to watch the fireworks on that day. Each year of the day, a ceremony to honor Tangun is held at the Chamseongdan altar at the summit of Mt. Manisan. This altar is said to have been built by Tangun and is a legendary place of worship and sacrifice favored by ancient kings during Korean history.