Cheomseongdae is the oldest existing astronomical observatory in Asia. It was constructed during the reign of Queen Seon-deok (632-647). The purpose of the obervatory was observing the stars in order to forecast the weather. The structure is a beautiful combination of straight lines and curves. On December 20th, 1962, it was designated as National Treasure No.31
Cheomseongdae was built in a cylinder shape with stones 30cm in diameter. The structure is made up of 362 stones spread over 27 levels. Roughly 4.16 meters up from the bottom there is a 1㎡ square entrance and a space to hang a ladder under it.The inside is filled with soil up to the 12th level. The 19th, 20th, 25th, and 26th levels all have long rocks hanging on two areas, shaped as the Chinese letter ‘井’ (jeong).
It stands 9.17 meters high and the base stone on each side measures 5.35 meters. The Vernal Equinox, Autumnal Equinox, Winter Solstice, Summer Solstice and the 24 solar terms (also known as the astronomical solar year) were determined by the observation of stars. The pavilion stone is believed to have been used as a standard of deciding directions, north, south, east and west. The 362 stones used to build Cheomseongdae represented the 362 days in a lunar year.
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