What is the North Star?

by Fraser Cain on January 26, 2009

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Were you wondering about the North Star? Firstly, you might expect one of the most famous stars in the night sky to be one of the brightest, but it isn’t; not by a long shot. That honor belongs to Sirius and many less bright stars besides. The North Star shines with a humble brightness that belies its navigational importance.

Polaris, or the North Star, sits almost directly above the North Pole; therefore, it is a reliable gauge of North if you find yourself lost on a clear night without a compass. Stars that sit directly above the Earth’s North or South Pole are called Pole Stars. Interestingly, the North Star hasn’t always been, nor will it always be the Pole Star because the Earth’s axis changes slightly over time, and stars move in relation to each other over time.

You can also approximate your latitude by measuring the angle of elevation between the horizon and the North Star. There is no equivalent star in the South Pole, but Sigma Octantis comes close. It isn’t very useful for navigational purposes as it isn’t very bright to the naked eye. Instead, navigators use two of the stars in the Southern Cross, Alpha and Gamma to determine due South.

The North Star is easy to find if you can first locate the Little Dipper. The North Star lies at the end of the handle in the Little Dipper (Ursa Minor). For a point of reference, The Big Dipper (Ursa Major) lies below the little dipper and their handles point in opposite directions. The two stars in the end of the ladle of The Big Dipper point to Polaris. Also, both The Big Dipper and The Little Dipper remain in the sky all night long, rotating in relation to the Earth’s axis.

We have written many articles about stars on Universe Today. Here’s an article that talks more about how the North Star is actually a variable star. And it’s really three stars in one.

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

References:
http://stars.astro.illinois.edu/sow/polaris.html
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980203a.html

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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