Cheomseongdae: The Oldest Observatory Where Humans Read the Sky
For thousands of years, humans have looked to the sky as a source of guidance and knowledge. The movements of the sun, moon, and stars were not only used to determine time and seasons, but also played a vital role in life, agriculture, and even the beliefs of ancient societies. It was out of this need to understand the regularity of the heavens that various civilizations began constructing dedicated sites for astronomical observations. One of the most famous relics is Cheomseongdae, an ancient observatory from Korea that testifies to how ancient humans attempted to read and understand celestial movements long before the development of modern technology.
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Cheomseongdae is a symbol of early astronomy and the first observatory in East Asia, located in South Korea. Cheomseongdae Silla is located in Gyeongju. This city was formerly the capital of the Silla kingdom, known as Seorabeol. Its exact location is not far from Ponweolseong Palace, at coordinates 35°49'53" N and 129°13'20" E. Korean historical records indicate three places named Cheomseongdae. The first is in Pyongyang, formerly the capital of the Goguryeo kingdom and now the capital of North Korea. The building no longer exists. The second is in Gyeongju, the capital of the Silla kingdom, which we will discuss here. And the last is in Gaeseong, North Korea, which is a relic of the Goryeo kingdom.
History of Cheomseongdae
Cheomseondae was built in 634 during the Silla Kingdom. This ancient observatory is located near the tomb of the Silla king Naemul. According to historians, this astronomical structure was constructed during the reign of Queen Sondok, the 27th ruler of the Silla Kingdom. Queen Sondok (Seon-deok) was one of the first female rulers in East Asian history.According to historical records in the Samguk Yusa or (Memories of the Three Kingdoms), Cheomseongdae was built during the reign of Queen Seondeok around 633–647 CE. Although the exact date of its construction or its primary function is not specified, various historical accounts and subsequent literary works mention that Cheomseongdae was used to observe the constellations and the movement of the Sun. Ancient Chinese records also suggest a similar astronomical function for the building.
Modern research into Cheomseongdae was first conducted by Tadashi Sekino, who concluded that the building was an observatory, although its shape and structure were unusual for a celestial observatory. Several years later, Japanese meteorologist Yuji Wada surveyed the site in 1909 and stated that Cheomseongdae was likely the oldest observatory in East Asia. He also believed that some parts of the building, including the interior staircase, had been lost over time.
Korean scholar Hong I-seup, in his book on the history of Joseon Dynasty science, stated that the Silla Kingdom conducted astronomical observations independently. He cited Cheomseongdae as crucial evidence and called it the oldest surviving observatory in East Asia. Meanwhile, Hong Sa-jun, who conducted a scientific survey of Cheomseongdae's stone structure, argued that astronomical observations were likely conducted from within the building, with the observer lying face-down facing the sky.
Initially, Cheomseongdae was generally believed to be an astronomical observatory. However, since the 1960s, various views have emerged regarding the building's true function. Yi Yong-beom argues that Cheomseongdae may have been an altar inspired by Mount Sumeru, a sacred mountain in Buddhism. Park Seong-rae shares a similar view, believing that Cheomseongdae is indeed related to astronomy in a broader sense, but is more accurately understood as an altar honoring the god of agriculture, held sacred by the people at that time.
Cheomseongdae Architecture and Construction
Cheomseongdae is composed of 27 layers of granite, arranged like bricks, forming a circular cylindrical structure. These layers support the square top of the building, which is supported by four parallel stone blocks. The granite-laying technique is said to bear similarities to the construction methods of Bunhwangsa, which was influenced by Tang Dynasty Chinese architecture.The building consists of approximately 362 granite blocks believed to represent the days of the lunar calendar. At the top is a rectangular stone array believed to have been used to mark the cardinal directions: north, south, east, and west. Twelve layers of stone are located below the windows, while another twelve layers are located above them. These numbers are believed to represent the twelve months of the year. The observatory stands approximately 9.17 meters high, with each side of the base measuring approximately 5.35 meters.
Approximately four meters above ground level is a rectangular opening believed to have served as the entrance and a stairway leading to the interior of the building. The interior is filled with earth up to the 12th floor. On the 19th, 20th, 25th, and 26th layers, there are long stones arranged in the shape of the Chinese character "井" (*jeong*), which is believed to be related to the traditional zodiac symbol.
Many researchers believe that the structure of Cheomseongdae reflects the Chinese calendar through its symbolic arrangement of stones. In addition to representing the days of the year, some parts of the building are also believed to represent the reign of Queen Seondeok. To this day, Cheomseongdae retains its original shape from over 1,300 years ago. Although the structure tilts slightly to the northeast, much of the structure remains intact, one of the most significant ancient astronomical relics in East Asia.
The World's Oldest Recognized Observatory
In 1982, Guinness World Records designated Cheomseongdae in South Korea as the world's oldest astronomical observatory still standing. Similar recognition was also made by the International Council on Monuments and Sites (ICOMOS), in collaboration with the International Astronomical Union, naming Cheomseongdae as the oldest observatory in East Asia. This recognition makes Cheomseongdae not only significant as a historical relic of Korea, but also as a world astronomical heritage site.However, this does not mean that there were no older observatories before Cheomseongdae was built. Long before the Silla Kingdom, great civilizations such as Egypt, Babylon, and Greece were familiar with astronomy and likely had their own celestial observatories. However, most of these ancient structures no longer survive intact or remain only in ruins and historical records.
In the 7th century AD, the Silla Kingdom itself was not the greatest power on the Korean Peninsula compared to neighboring kingdoms like Goguryeo and Baekje. Interestingly, historical records also mention that a similar structure to Cheomseongdae existed in the Goguryeo region, but its physical traces have been lost over time. Therefore, Silla's Cheomseongdae is the only ancient observatory still visible, surviving more than 1,300 years later, making it an important symbol of the development of astronomy in East Asia.
Cheomseongdae Sparked Controversy
Most researchers believe that Cheomseongdae served as an astronomical observatory. This view is supported by various historical records from Korea, Japan, and China, which mention the building's connection to celestial observation. At that time, astronomical observations were conducted with the naked eye and aided by simple instruments such as the gnomon, a sun-shadow indicator used to determine the time and position of celestial bodies. Through these observations, combined with a calendar system, the Silla people were believed to be able to predict eclipses, seasonal changes, and the positions of constellations, which were also closely linked to astrology and royal life.However, not all researchers agree on Cheomseongdae's astronomical function. Some experts consider the building's shape less representative of an observatory. Lee Yong-beom of Dongguk University, for example, argues that Cheomseongdae is more of a symbol of Mount Sumeru, which holds significant significance in Buddhist cosmology. Meanwhile, Kim Yong-un of Hanyang University believes the building was likely built as a monument to the Silla Kingdom's high scientific achievements during its time.
Despite differing views, the theory that Cheomseongdae was an observatory remains the most widely accepted. Some modern researchers have even attempted to reconcile the two views, arguing that Cheomseongdae was likely used for astronomical observation, but its architectural design and symbols were still influenced by Buddhist beliefs and culture that flourished during the Silla Kingdom.
Author : Muhammad Faizal Akbar (Astronomy Enthusiasts)
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