Does the North Star ever move?
Polaris sits almost at the center of these spinning stars. But it is offset slightly from the exact north pole of the celestial sphere. (Jeff Fennell)
Does the North Star ever move relative to Earth … or relative to anything for that matter?
The North Star, also known as Polaris, is a star like any other. All the stars we see in our night sky are members of the Milky Way galaxy. All of these stars are moving through space, but they’re so far away we can’t easily see them move relative to each other. That’s why the stars appear “fixed” relative to each other. And it’s why – for the most part – we see the same constellations as our ancestors.
But Earth spins underneath the stars once a day. Earth’s spin causes the stars to rise in the east and set in the west, just as the sun does. When you’re talking about this kind of movement, the North Star is a special case. It lies almost exactly above Earth’s northern axis. So Polaris is like the hub of a wheel. It doesn’t rise or set – instead, it appears to stay put in the northern sky.
That’s how the eye sees it, anyway. The North Star is really offset a little from celestial north. If you took its picture, you’d find that it makes its own little circle around true north every day. What’s more, the star we know as Polaris hasn’t been the only North Star.
A motion of Earth called precession causes our axis to trace out an imaginary circle on the celestial sphere every 26,000 years. Thousands of years ago, when the pyramids were rising from the sands of ancient Egypt, the North Star was an inconspicuous star called Thuban in the constellation Draco the Dragon.
Twelve thousand years from now, the blue-white star Vega in the constellation Lyra will be a much brighter North Star than our current Polaris.
By the way, Polaris could be a name for any North Star. Our current Polaris used to be called Phoenice.
(Image at right by John Mora)
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