Thuban

Archaeologists know of only a few major artifacts of the pharaoh Khufu, who ruled Egypt more than 4500 years ago. The list includes some small statuettes — some of which might have been created long after his reign. But one artifact is at the opposite end of the size scale: the Great Pyramid of Giza, one of the seven wonders of the ancient world.

The pyramid was built with the help of a guiding light — the star Thuban. At the time, it was the Pole Star. It marked due north in the sky, making it a good tool for laying out the pyramid. And as the Pole Star, it was the hub of the sky, with all the other stars rotating around it — a position that held great power for many cultures.

Thuban stands due north as the sky gets dark right now. It’s in Draco, the dragon, high above today’s Pole Star, Polaris. Thuban isn’t very bright, so it’s hard to see from light-polluted cities.

Thuban lost its position as the north celestial pole because of an effect known as precession. Earth wobbles on its axis like a gyroscope that’s running down. It takes 26,000 years to complete a single wobble. During that time, Earth’s axis draws a big circle on the northern sky, so different stars take turns marking the pole.

Thuban held that position for a couple of thousand years, including the time when Khufu’s pyramid was built. It’ll return to that celebrated spot in the sky again — in about 20,000 years.

Script by Damond Benningfield