Cheomseongdae Observatory

Site details

Cheomseongdae, believed to have been constructed during the reign of Queen Seondeok of Silla (r. 632-647), is considered the oldest existing astronomical observatory in East Asia and a valuable cultural heritage site that demonstrates the advanced scientific knowledge of the time. As an astronomical observatory used during the Silla period to observe celestial movements, Cheomseongdae features a base (gidanbu) that supports a cylindrical body shaped like a bottle, topped with a square-shaped platform (jeongsangbu). The structure stands at approximately 9 meters tall. The cylindrical body of Cheomseongdae is constructed with 27 layers of fan-shaped stones. While the exterior is smoothly finished, the interior walls are uneven, with the rough ends of the stones protruding irregularly. The lower portion of the structure is filled with rubble up to the window on the southeast side, above which the interior is hollow all the way to the top. The top section, which is partially sealed with slab stones on the eastern half, features a square-shaped design where the ends of long stones interlock and extend outward. Similar projections of stone can be observed at the 19th-20th and 25th-26th layers, suggesting they were likely used to support ladders. According to ancient records, "a person could ascend through the middle," indicating that observers would place a ladder against the exterior, enter through the window, and then use an internal ladder to climb to the top to observe the sky. Astronomy is closely related to agriculture, as it allowed ancient civilizations to determine the timing of farming activities based on the movements of celestial bodies. Additionally, astrology, which involved predicting a nation's fortunes based on astronomical observations, was of immense importance in ancient states, indicating a strong connection between astronomy and politics. As a result, astronomy became a major focus of national interest early on, likely providing a strong rationale for the construction of Cheomseongdae. Photo Credit: Gyeongju Tourism Resource Video Images provided by Gyeongju Tourism