The Ganui Platform and Armillary Spheres
Also called: Honcheonui, Ganui, Ganuidae
King Sejong built the observation platform Ganuidae at Gyeongbokgung and had the simplified armillary (ganui) and armillary sphere (honcheonui) made.
문화재청 (공공누리 제1유형) · CC BY-SA 4.0 · Source
In 1432 Sejong had Jeong In-ji and Jeong Cho study the old astronomical texts and Yi Cheon, Jang Yeong-sil and others build instruments. A wooden ganui was made first to measure the altitude of the pole at Hanyang, then a bronze ganui, and the armillary sphere was completed in 1433. A tall stone platform, the Ganuidae, was built north of Gyeonghoeru in Gyeongbokgung, where astronomers of the Seoungwan watched the sky every night.
The ganui is a simplified armillary with fewer rings, made for measuring the angular positions of heavenly bodies; the honcheonui (armillary sphere) uses nested rings to model and observe the motions of the sun, moon and stars. These observations underlay the Chiljeongsan (1442), a calendar calculated for Hanyang. None of the instruments of Sejong’s day survive; replicas exist today.
