Cheomseongdae is an astronomical observatory in Gyeongju, South Korea. Cheomseongdae means star-gazing tower in Korean. ---- Cheomsongdae is is an astronomical observatory in Gyeongju, South Korea. Cheomseongdae means stargazing tower in Korean. Cheomseongdae is one of the oldest surviving observatories in East Asia, and one of the oldest scientific installations on Earth.