Yi Sun-ji

Yi Sun-ji (1406-1465) was a scholar-official and astronomer active during the reign of King Sejong in Joseon Korea. Rather than simply following the Chinese calendar as had long been the custom, he played a major role in compiling the Chiljeongsan, a calendrical treatise that calculated the movements of the sun, moon, and planets based on the meridian of Hanyang (present-day Seoul). By creating a calendar suited to Korea's own skies and conditions, he helped raise the level of Joseon astronomy.