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Cheomseongdae is the oldest observatory in East Asia that still exists, and it has been designated as a national treasure.

Cheomseongdae is the oldest observatory in East Asia and is known to have been built for observing the sky.

There are various opinions about its purpose, including that it was built as a symbol of astronomy or as an altar for conducting rituals to the sky. However, most consider Cheomseongdae to have been an observatory.

An observatory refers to a tower built for observing astronomy, which is the study of the laws of the heavens and the universe.

During the Three Kingdoms period when Cheomseongdae was constructed, it held significant importance. It was utilized for both mystical purposes to divine the fate of the nation and for predicting the weather. Through Cheomseongdae, careful observations were made of changes occurring in the sky. In particular, observational activities for weather prediction evolved into the “astronomical calendar system.,” a method of distinguishing seasons by examining how the sun, moon, and the five nearby stars moved in relation to Earth. This later became instrumental in weather prediction and calendar-making.

The primary reason ancient people built observatories and observed the sky, as they did, was primarily for agricultural purposes.

During that time, agriculture was heavily dependent on weather conditions, unlike today. Furthermore, since agriculture served as the foundation of the national economy, astronomy was of utmost importance.

Cheomseongdae was based on astronomy from the beginning of its construction.

Cheomseongdae was constructed using 362 stones, which is similar to the number of days in a year (365). These 362 stones were used to build a total of 28 tiers, symbolizing the 28 constellations. The lower and upper sections, each consisting of 12 tiers of stone, represent the 12 months and 24 solar terms in a year. Additionally, there are traces of a ladder on the southern-facing window between the 13th and 15th tiers, indicating that this window was used not only for access but also for astronomical observations. In fact, the amount of light entering through Cheomseongdae’s windows can be used to measure the solar terms such as Chunbun (Vernal Equinox), Haji (Autumnal Equinox), and Chubun (Winter Solstice).

Cheomseongdae has a cylindrical shape resembling Silla earthenware.

As you go up, it narrows, giving a sense of stability. Windows were placed in the weakest part. Additionally, capstones were used to reinforce the main body. This construction method is similar to the one used in the construction of the Eiffel Tower in France, which was built 100 years ago, highlighting the advanced architectural technology of that time.

Additional features of Cheomseongdae

• At the top, a stone in the shape of the character ‘井 (jung)’ was placed, and each of its sides precisely aligns with the four cardinal directions: east, west, south, and north.
• Cheomseongdae has endured the test of time and remains very robust. The use of stones of varying sizes carefully stacked together prevented it from easily collapsing. Up to the 12th tier with doors, a mixture of earth and small stones was compacted to create a solid wall.
• The window located midway on Cheomseongdae also served as an entrance, where a ladder was placed for researchers to access. Traces of the ladder remain visible to this day.

Do you also consider Cheomseongdae to have been the oldest observatory in East Asia? What are your thoughts?