Astronomy EssentialsSpace

# Does the North Star ever move?

### The North Star, aka Polaris

The North Star, also known as Polaris, appears to stay fixed in our northern sky. It marks the location of the sky’s north pole, or the north celestial pole, the point around which the whole northern sky – full of stars – turns. That’s why you can always use Polaris to find the direction north.

So the North Star doesn’t appear to move. But it does move. If you took its picture, you’d find that it makes its own little circle around the exact point of the north celestial pole every day. That’s because the North Star is offset a little – by about 0.65 degrees – from celestial north. So Polaris makes a circle that’s 1.3 degrees in diameter each day. When it’s closest to the celestial pole in about 100 years, at a distance of only 0.45 degrees, it’ll make a daily circle of only 0.90 degrees.

Where does this movement – or in Polaris’ case, lack of movement – come from? It comes from Earth’s spin. Earth spins under the sky once a day, and our spin causes the sun in the daytime – and the stars at night – to rise in the east and set in the west. But the North Star is a special case. Because it lies almost exactly above Earth’s northern axis, it’s like the hub of a wheel. It doesn’t rise or set. Instead, it appears to stay put in the northern sky.

### How high in your sky?

The North Star not only points one toward the north, but its height in the northern sky also matches your latitude on earth. If you are sailing the Caribbean at 16° north latitude, the north star will be about 16° high in your sky. If you are sailing around Nova Scotia, at 44° north latitude, then the North Star will be about 44° high in your northern sky. Each degree north or south equals 69 miles (111 km), so traveling 690 miles north or south will change your latitude, and the North Star’s elevation, by 10 degrees.

Read more: Polaris is the North Star

### Taking turns as the 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.

Polaris could be a name for any North Star. Our current Polaris used to be called Phoenice. It is the 49th brightest star in the sky. It is not known for its brightness, but for its unique position in the sky.

### Proper motion

By the way, Polaris – like all stars – has more than one kind of motion. The stars we see in our night sky are all members of our 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 over time, this movement, called proper motion rearranges the patterns of stars we see in our sky. For Polaris, that movement is small, about 46 arcseconds in 1,000 years. That is about 1/40th of the diameter of the full moon as seen from the earth. So when you’re talking about stars moving or staying fixed, remember … they are all moving through the vastness of space. It’s just the relatively short time of a human lifespan that prevents us from seeing this grand motion.

Bottom line: The North Star is a symbol for constancy. But, if you took its picture, you’d find that it makes its own little circle around the sky’s north pole every day.

Posted
October 4, 2023
in
Astronomy Essentials