Although Polaris marks the north celestial pole today, it won't maintain that location for long. Earth wobbles on its axis like a spinning top, so the polar axis draws a wide ring on the sky. Over the millennia, that ring will pass by several bright stars, giving Earth a succession of pole stars. This diagram provides a rough idea of this path and the epoch in which each star will take its place as the North Star.
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Perhaps the most famous star in the night sky is Polaris. It’s not especially bright or close by. Instead, it’s famous for its location. It marks the north celestial pole, so it’s also known as the North Star or the Pole Star. Right now, it’s about two-thirds of a degree from the true celestial pole. But over the next century, it’ll snuggle even closer.
The change is caused by a slow “wobble” in Earth’s rotation. Over a period of 26,000 years, that causes the planet’s axis to draw a big circle on the sky. So while Polaris itself will still be around, it won’t keep its position as the North Star.
The axis is sweeping counterclockwise. So the next moderately bright star it’ll point to is Gamma Cephei, which is to the right or lower right of Polaris as darkness falls this month. It’ll take over as the North Star in about 3,000 years.
After moving past another star of Cepheus, the pole will take aim at Deneb, the “tail” of Cygnus, the swan, around the year 10,000. And 3500 years later it’ll be the brightest pole star of all, Vega. Neither Deneb nor Vega will be all that close to the true celestial pole, but their brilliance will make up for the gap.
And in about 20,000 years, the pole will come around to Thuban. It marked the pole about 4,500 years ago, when it helped architects align the pyramids of Giza. Finally, around the year 28,000, the pole will return to Polaris — closing its great circle on the sky.
Script by Damond Benningfield, Copyright 2012
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