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June 13, 2015

Archaeologists know of only two major artifacts of the pharaoh Khufu, who reigned over Egypt more than 4500 years ago. One is the smallest royal statue yet found — an ivory figurine just three inches tall. The other 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 — a star known as Thuban. At the time, it was the Pole Star. It marked due north in the sky, making it a good tool for laying out a structure. It was also the hub of the sky, with all the other stars appearing to rotate around it — a position that’s held great power for many cultures.

Thuban stands due north as the sky gets good and dark right now. It’s directly above today’s Pole Star, Polaris, in Draco, the dragon. It’s not very bright, though, 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 spinning top 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. And it’ll return to that celebrated spot in the sky again — in about 20,000 years.

We’ll talk about another pole star tomorrow.


Script by Damond Benningfield, Copyright 2015

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