Gaecheon (or "Opening of Heaven") refers to 3 October B.C. 2457, the date when Hwanung (환웅) descended from heaven to live with mankind.
The harvest ceremony was celebrated in each Korean kingdoms; Yeonggo (영고) of Buyeo, Mucheon (무천) of Yemaek, Gyeeum (계음) of Mahan and Byeonhan, Dongmaeng (동맹) of Goguryeo, Palgwanheoi (팔관회) of Silla.
In 1909, Gaecheonjeol was enacted as a national holiday. The festival is held annually. At first, Gaecheonjeol had been celebrated on the 3rd day of the 10th month on the lunar calendar but it has been celebrated on 3 October on the solar (Gregorian) calendar since 1949.