The stars have guided human actions for thousands of years. Farmers used the stars to tell them when to plant and harvest crops. And kings and queens used them to pick the best times for wars, coronations, weddings, and other big events. So it was important to find the right spot for watching the stars. Often, that meant building an observatory — a structure with a clear view of the night sky.

An example is Cheomseongdae — a name that means “star-gazing platform,” in South Korea. It’s the oldest-known surviving observatory in eastern Asia, dating back almost 1400 years.

The observatory is a 30-foot tower made from granite blocks. The tower is shaped like an old milk bottle — wider at the base than at the top. A wider tier sits atop it. Seen from above, that tier forms an Asian character for the word “well.”

The tower consists of 365 blocks — one for each day of the year. The entire structure consists of 30 tiers — the number of days in a lunar month. And its base consists of 12 stones — perhaps representing the number of months in a year.

No one is sure just how Cheomseongdae was used to watch the stars. There’s a window half way up the tower. An observer might have climbed to the window on a ladder, then climbed a ladder on the inside to reach the top. From that high perch, the observer could watch the stars, Sun, Moon, and planets — perhaps using them to help guide the people of ancient Korea.

Script by Damond Benningfield

Support McDonald Observatory