Polaris – Facts for Kids
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 called Merak and Dubhe. They are the pointer stars because 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 of the Earth, and a real pole there is pointing straight into the night sky. It would point towards Polaris. In other words, Polaris would be directly above you.
We don't have a star that we can use as a south polar star.
There is a star that isn't far from the celestial South Pole. It's called Sigma Octantis. Unfortunately, it's faint and hard to see. Astronomers term it a sixth-magnitude star. The bigger its magnitude number, the dimmer a star is. Sixth-magnitude stars are the dimmest ones we can see without binoculars. Polaris is a second magnitude star, so it's fairly bright, but you could only see Sigma Octantis in a very clear dark sky.
All the stars seem to move during the night – except Polaris.
The stars aren't going anywhere, but 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. In this picture you can see stars trails with Polaris in the center. Since Polaris is in line with Earth's north polar axis, it doesn't seem to move.
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 fairly 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.
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