Scientific and Institutional Reforms under Sejong (1430s)

Timeline

1. 1431–1433Office of Astronomy, Hanseong · Joseon dynastySejong ordered scholars of the Jiphyeonjeon and the Office of Astronomy to systematically observe the sun and moon, referencing Chinese Yuan and Ming calendars while adjusting for Korea's latitude, accumulating observational data for later works such as the Qizheng Suan Neipian.
2. 1434Hanseong · Joseon dynastyCraftsmen including Jiang Ying, with court support, produced a large self-striking clepsydra (Gayeong clock) driven by water power to announce the hours, marking a new height in Korean precision timekeeping, complemented by sundials and gnomons for shadow measurement.
3. 1435–1440All of Joseon · Joseon dynastyThe court promoted rain gauges, humidity observation, and records of agricultural timing, combining astronomical observations with agricultural policy and disaster relief to form a practical scientific network serving state governance.