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Stargazing in Ancient Silla – the Cheomseongdae

Cheomseongdae, the world’s oldest surviving observatory, features a great deal in tourism material, and even if you haven’t been to Korea or the Gyeongju area, you will probably have seen it. You will also, if you are like me, have been somewhat underwhelmed by its rather modest appearance, which if anything does it less justice when seen in real life. At 9.5 metres in height it is a relatively small structure.

photo of Chomsongdae - a stone observation tower

Though modest in appearance, in terms of functionality it was without peer, and was used as the basis for famous observatories in China and Japan.

Its design was also carefully thought-out, so that each of its features carries a meaning.

The astronomical concept that the earth is square and the sky is round, for example, is reflected in the square base and round body. The 29 layers of stone correspond to the 29.5 days of a lunar month, with the 27 layers of the cylindrical body representing the 27 days taken for the moon to circle the earth. The list of symbolic references in the design goes on at some length, with features reflecting the months and seasons. The total number of stone slabs used in the round body is 364, which combined with the horizontal slab at the top, make the total number of days in a year.

The astronomer gained access via the middle window, and scaled the tower from the inside by means of a ladder.

The location of the tower within the palace grounds may seem puzzling. Nowadays, light and air pollution dictate that observatories must be built in remote locations, but neither of these were issues in Silla Korea. Their presence within the palace grounds is testament to the political importance of astronomical readings (of which more in other posts).

Finally, the dimensions of the tower were carefully matched to the surroundings, ensuring an unobstructed view of the skies. The view is not obscured by trees shorter than 9m in the immediate vicinity. Likewise, a tree 15m tall at a distance of 50m, or a 20m tree at a distance of 100m, is visible only at an angle of elevation of 6 degrees or less.

Standing unassumingly among the tombs of the Silla kingdom in Gyeongju, the Cheomseongdae stands testament to the Korean values of efficacy, beauty and modesty, so often found together in the same object.


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