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| Brightest Stars on May 27, 2013

Polaris is the North Star

The entire northern sky wheels around Polaris. Some assume it’s the brightest star in the sky. In fact, Polaris ranks only 50th in brightness.

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 relatively easy to see. That fact has made this star a boon to travelers throughout the Northern Hemisphere, both over land and sea. Finding Polaris means you know the direction north.

Polaris on a stormy night. Spotting the North Star – and in that way knowing the direction north – has gladdened the heart of many a lost traveler. Photo by EarthSky Facebook friend Jv Noriega in the Philippines.

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.

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: the Big Dipper.

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’s bowl. Simply draw a line from Merak through Dubhe, and go about 5 times the Merak/Dubhe distance to Polaris.

If you can find the Big Dipper, you can find Polaris. The two outer stars in the bowl of the Dipper – Dubhe and Merak – always point to the North Star. The chart is for a Northern Hemisphere late winter/early spring.

Does the North Star ever move?

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!

Polaris marks the end of the Handle of the Little Dipper. Chart for early autumn evening Image via EarthSky Tonight

By the way, 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 Little Dipper is tougher to spot in the night sky than the Big Dipper. But if you use the Big Dipper’s pointer stars to locate Polaris, you’ll be one step closer to seeing the Little Dipper.

History

Polaris hasn’t always been the North Star and won’t remain the North Star forever. For example, a famous star called Thuban, in the constellation Draco the Dragon, was the North Star when the Egyptians built the pyramids. But our present Polaris is a good North Star because it’s the sky’s 50th brightest star. So it’s noticeable in the sky. It served well as the North Star, for example, when the Europeans first sailed across the Atlantic over five centuries ago.

Star Errai: Future North Star

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 – on March 24, 2100. The computational wizard Jean Meeus figures Polaris will be 27’09″ (0.4525o) from the north celestial pole at that time (a little less than the angular diameter of the moon when at its farthest from Earth).

Meanwhile, there is no visible star marking the celestial pole in the Southern Hemisphere. What’s more, the Southern Hemisphere won’t see a pole star appreciably close to the south celestial pole for another 2,000 years.

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.

When you take a time exposure photograph of the northern sky (or, in this case, the northeast), you see all the stars are moving around Polaris, which is on the left in this image. This image by Taro Yamamoto via an article on long exposure star trail photography.


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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.

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

Science

An artist’s illustration of Polaris and its two known companion stars via the Hubble News Center.

The single point of light that we see as Polaris is actually a triple star system, or three stars orbiting a common center of mass. The primary star, Polaris A, is a supergiant with about six times the mass of our sun. A close companion, Polaris Ab, orbits 2 billion miles from Polaris. Much farther away, near the top of the illustration at right, is the third companion Polaris B. Polaris B is located approximately 240 billion miles from Polaris A. The two companion stars are the same temperature as Polaris A, but are dwarf stars.

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