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Polaris, the North Star, has been a navigation star for 1500 years. Anyone who can find Polaris knows where north is. If you stand facing Polaris and stretch your arms out to your sides, then your right hand points east, and your left hand points west. I should add that this only works in the northern hemisphere.

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Polaris isn't hard to find.
Just start by looking for the Big Dipper (called the Plough in Britain). It's probably the best known group of stars in the sky. The two stars that are farthest from the handle are the pointer stars Merak and Dubhe. If you follow an imaginary line through them, it points to Polaris. The Dipper appears to move around Polaris as the Earth turns, but Merak and Dubhe still always point to Polaris.

Polaris shows where north is, because it just happens to be in line with the North Pole of the Earth.
Imagine you're at the North Pole, and also imagine a real pole pointing straight into the night sky. It would point towards Polaris. In other words, Polaris would be directly above you.

All the stars seem to move during the night – except Polaris.
Since Polaris is above the north pole, it doesn't seem to move. But the other stars seem to move around Polaris as the Earth turns. You can take a picture of this movement using a long exposure on a camera. As Earth turns, the light from the stars makes star trails. The header image shows some star trails. Polaris is a dot near the top of the picture to the right of the center.

We don't have a star that we can use as a south polar star.
There is a star called Sigma Octantis that's not far from the celestial South Pole. Unfortunately, it's faint and hard to see. The biger the magnitude number, the dimmer a star is. And Sigma Octantis is a sixth-magnitude star, so it's one of the dimmest we could see without binoculars. It would still need a clear dark sky. Polaris is a second magnitude star, so it's fairly bright. That makes it useful for navigation.

Polaris hasn't always been the pole star.
People have used Polaris for navigation since the fifth century. But when the Egyptians built the pyramids, Thuban (in the constellation Draco) was the north pole star. Vega (in the constellation Lyra) will be the pole star twelve thousand years from now. Earth's axis has a little wobble, so during 26,000 years the pole moves in a little circle and points to different areas of the sky.

Polaris is actually three stars.
Polaris A is the main star, a supergiant with nearly five times the mass of the Sun. It's also a Cepheid variable. Most stars have a constant brightness, but the brightness of variable stars goes up and down. Cepheids are a special kind of variable star that astronomers can use to measure the distances to galaxies and star clusters.

Polaris B is a companion to Polaris A, and is similar to the Sun. William Herschel discovered it in 1780. Polaris A and B are far enough apart that you can see both of them with good binoculars.

Polaris Ab has about the same mass and luminosity (brightness) as Polaris B. But it took until 1929 to realize that there was a third star in the system. No one could see it directly, but when they studied the light spectrum of Polaris A, it showed that the light of two stars were mixed together. Polaris Ab is so close to its big bright neighbor that it it needed the power of the mighty Hubble Space Telescope to see it. In 2006 it imaged the companion which had been invisible before.