Cheomseongdae Observatory

Cheomseongdae, whose name means "star-gazing tower", is a stone structure built in Gyeongju during the reign of Queen Seondeok of Silla (632–647). It is regarded as the oldest surviving observatory in Asia, was designated a National Treasure on 20 December 1962, and is part of the UNESCO World Heritage Site "Gyeongju Historic Areas".

History and structure

The earliest record of Cheomseongdae is in the Samguk yusa, which dates it to Queen Seondeok's reign. Other chronicles give different years, including 633 and 647. It stands on flat ground north of Wolseong, the site of the Silla royal palace, in what is now central Gyeongju.

The body is a cylinder of granite blocks in 27 courses. Sources differ on its height, 9.17 m or 9.4 m, and on the number of stones: 362, 365 or 366. If it is 365, the stones may stand for the days of the year, but the count depends on which stones you include. Halfway up, a square window faces due south; below it, the interior is filled with earth up to the 12th course. On top sit two tiers of stones laid in the shape of the character 井, "well", which is what you would see from above. The square base is given as 5.35 m or 5.7 m a side, depending on the source.

What to see

• The south window: there are 12 courses below it and 13 above, so it sits right in the middle. People probably climbed in using a ladder.
• Round body, square top: some read it as an image of the old belief that heaven is round and the earth square. Others link the 27 courses to Queen Seondeok, the 27th ruler of Silla.
• The lean: reports in 2005 put the tilt at about 7.2 cm to the north and 2.4 cm to the east, and since 2007 its condition has been monitored continuously.
• The setting: the observatory stands in open lawns and flower fields that change with the seasons, and it is floodlit at night.

Good to know

• Whether it was really used to watch the stars is still debated. Since the 1960s scholars have suggested it was part of a sundial, an altar or a political monument.
• On the other side, Silla's astronomical records increased more than tenfold after it was built, which supporters see as evidence for its use as an observatory.
• After the 2016 Gyeongju earthquake the stonework shifted by about 1.2 cm, but no cracks appeared.
• The south window looks straight towards Banwolseong, where the Silla palace stood.
• In the 2009 TV drama Queen Seondeok, building the observatory is shown as her first decree as a princess.

Tripto tips

• Visiting: you view the tower from outside a low fence. Check opening hours and fees on the Gyeongju city tourism website.
• Time needed: 30 minutes for the tower alone. Walk on to the Daereungwon tomb park, the Wolseong palace site and Donggung Palace and Wolji Pond for a half-day stroll.
• When to go: early evening, as the lights come on, is best for photos. It gets busy when the spring and autumn flower fields are in bloom.
• Getting there: it sits on flat ground east of Daereungwon in central Gyeongju, easy to reach on foot or by bike from town-centre accommodation.