Korean Stargazing Tower: Cheomseongdae
According to Samguk Yusa, Cheomseongdae was constructed under the reign of Queen Seondeok (632-647) near Gyeongju, the capital of Silla. Cheomseongdae means star gazing platform. The tower is built out of 362 pieces of cut granite which represent the 362 days of the lunar year.
It has 27 circular layers of stones which some associate it with the fact that Queen Seondeok was considered to be the 27th ruler of Silla or the constellation of stars surmounted by a square structure. 12 of the layers are below the window level and 12 are above. There are 12 large base stones set in a square, with three stones on each side. These sets of 12 may symbolize the months of the year.
The tower is 4.93 meters wide at the base and 9.17 meters tall, and filled with earth up to the level of the window. Cheomseongdae is the oldest existing astronomical obsevatory in the Eastern hemisphere.
There isn't a door in Cheomseongdae. So, we might have thought that is it real observatory. And, that's why there were suggestions that the Cheomseongdae was used as an altar not an observatory. We don't need special facilities like Choemseongdae to observe the stars. We only need plain space to observe. In fact, ancient people had observed without the observatory like Choemseongdae.
However, the problem is this. Because of the bad weather or private reasons astronomers might skip the observations. Then, we could not get information in that day. Therefore they might needed the system that astronomers must observe the stars every day. And, that's why the Chomseongdae had constructed. This is the reason why there isn't a door in Cheomseongdae. There isn't a door, so we have to use a ladder to get in or get out of Cheomseongdae. Astronomers must observed the stars all night because they could not get out of Cheomseongdae without a ladder. Also, it was easy to know that the astronomers were observing or not because they were in the high place
In modern perspective, it doesn't seem so good, but it did. For example, the records of astronomical observations had increased about 10 times after the construction of Cheomseongdae compared to the records before the construction of Cheomseongdae. Also, the qualities of observations had increased.
Cheomseongdae had helped the astronomy of Silla a lot.