EarthSky

July 1st, 2010 - Brightest Stars

How to see Polaris

The North Star or Pole Star – aka Polaris – is famous for holding nearly still in our sky while the entire northern sky moves around it. Polaris is not the brightest star in the nighttime sky, as is commonly believed. Polaris is only about 50th brightest.

Still, this star is bright enough to spot even from some suburban skies. In a dark country sky, even when the full moon obscures a good deal of the starry heavens, the North Star is still relatively easy to see.

Best of all, Polaris is readily found by using the prominent group of stars known as the Big Dipper, perhaps the northern hemisphere’s most famous star formation. To locate Polaris, all you have to do is to find the Big Dipper pointer stars Dubhe and Merak. These two stars outline the outer part of the Big Dipper bowl. Simply draw a line from Merak through Dubhe, and go about 5 times the Merak/Dubhe distance to Polaris.

Does the North Star ever move?

Polaris is famous for more reasons than one. It’s famous for hardly moving while the other stars wheel around it. And it’s famous for marking the end of the Little Dipper’s handle.

The Big Dipper, like a great big hour hand, goes full circle around Polaris in one day. More specifically, the Big Dipper circles Polaris in a counter-clockwise direction in 23 hours and 56 minutes. Although the Big Dipper travels around Polaris all night long, the Big Dipper pointer stars always point to Polaris on any day of the year, and at any time of the night. Polaris marks the center of Nature’s grandest celestial clock!

History

Polaris hasn’t always been the North Star and won’t remain the North Star forever. But this star well served as the North Star when the Europeans first sailed across the Atlantic over 5 centuries ago.

And Polaris will continue its reign as the North Star for many centuries to come. It will align most closely with the north celestial pole – the point in the sky directly above Earth’s north rotational axis – around the year 2100.

At one time in human history, people literally depended on their lucky stars for their lives and livelihood. Luckily, they could trust the Big Dipper and the North Star to guide them. People could sail the seas and cross the trackless deserts without getting lost. When slavery existed in the United States, slaves counted on the Big Dipper (which they called the Drinking Gourd) to show them the North Star, lighting their way to the free states and Canada.

Polaris marks the way due north. As you face Polaris and stretch your arms sideways, your right hand points due east, and your left hand points due west. About-face of Polaris steers you due south.

Does Mars have a North Star?

As you travel northward, Polaris climbs higher in the sky. If you go as far north as the North Pole, you’ll see Polaris directly overhead. As you travel south, Polaris drops closer to the northern horizon. If you get as far as the equator, Polaris sinks to the horizon. South of the equator, Polaris drops out of the sky.

Science

Astronomers estimate Polaris’ distance at 430 light-years. Considering the distance, Polaris must be a respectably luminous star. According to the star aficianado, Jim Kaler, Polaris is a yellow supergiant star shining with the luminosity of 2500 suns. Moreover, this single point of light that we see as Polaris is actually a binary – two stars orbiting a common center of mass. Polaris is also the closest and brightest Cepheid variable star – a type of star that astronomers use to figure distances to star clusters and galaxies.

Polaris, aside from being honored as the North Star, enjoys the title of Lodestar and Cynosure as well.

Polaris’ position is RA: 2h 31m 48.7s, dec: +89° 15′ 51″