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More Science Q&A

Everyday Einstein answers more reader questions about stars, soap scum, and baking soda.

By
Lee Falin, PhD
February 8, 2014
Episode #087

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The Not So Stable North Star

Fellow podcaster Grammar Girl wrote in this week to ask: 

“Why doesn’t the North Star appear to move through the sky like other stars? Is it that it's directly above our axis of rotation, so that we almost hang from it as if we were attached by a string?”

Yes, that’s exactly correct. I’m Lee Falin and this has been the Everyday Einstein podcast…wait, what? There’s a minimum episode length? Okay, I’ll explain a bit further.

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The Shocking Truth Behind the North Star

North StarIf you were to go to the North Pole, and fly straight up for 433 light years, you would run right into Polaris, A.K.A the North Star. Well, actually you’d be incinerated by the heat coming from the star long before you reached it. But, since we’re already pretending you can fly through space, I think we can take the fantasy just a bit further.

While you might know all there is to know about Polaris, there are some shocking truths that I recently uncovered that may interest you. First, Polaris isn’t just one star. It’s a triple star system that wasn’t confirmed visually until 2006

Aside from that, while Polaris’ position directly above the Earth’s axis of rotation gives it the illusion that it isn’t moving, the shocking truth is that it does move! According to one of my favorite astronomy websites, EarthSky.org, Polaris hasn’t always been the North Star...nor will it continue to be for much longer, all thanks to something called precession.

Second Star to the Right

If you’ve ever spun a top on the floor, you’ll notice that when the spin starts to slow down, the top starts to wobble. That’s because the earth’s gravity is pulling down on it. Well, the other planets, the sun, and the moon all pull on the Earth, giving it a bit of a wobble as well. This wobble in the Earth’s rotation is called precession and it causes the Earth’s axis to trace a large circle across the heavens every 26,000 years. 

As the axis moves over time, eventually the North Pole will no longer point at Polaris. In fact, to ancient civilizations, Polaris was never the North Star. A little star called Thuban in the constellation Draco was the star closest to the North Pole from around 4,000 BC until around 1,500 BC when a star in Ursa Minor took its place. Then, in 500 AD, Polaris moved in for the coveted North Star title. But by the time your great, great, great, however many greats, grandchildren are reading this in 3,000 AD, Polaris will have shifted out of position, and the star Gamma Cephei, A.K.A Errai, will have taken its place.

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