What's so Special About the North Star (Polaris)?
When asked to say the names of any stars, most people can at least say, "the North Star." When I present planetarium shows, "Where's the North Star?" is one of the most common questions I get after one of the rare programs that does not include a look at the northern sky. What is it that makes the North Star so popular? Sure, it's much easier to remember the name of the North Star than it is to remember star names such as Alberio or Fomalhaut, but what else is special about the North Star?
What exactly is the North Star?
Another name for the North Star is "Pole Star." A pole star is a star that is lined up with Earth's axis, and is therefore lined up with either the north or south celestial pole.Technically, this is more of a title than a specific name. The axis of Earth wobbles (this is called "precession"), and is therefore not always lined up with the same star. It takes 26,000 years for one complete "wobble," so it takes a long time for the title of "pole star" to pass on from star to star. Sometimes, such as during the first thousand years BC, there is no pole star at all. When there is a pole star, it appears more or less fixed in position, unlike the other stars that appear to move across the sky as the earth turns on its axis.
Currently, the star at the northern celestial pole is Polaris, which comes from the Latin name, stella polaris, which, interesting enough, means "pole star." One wonders if somebody will change the name in the year 3000 AD, when a star called Alrai will be closer to the pole than Polaris.
Polaris is not exactly at the pole of rotation, though it's only 7 tenths of a degree away. This means it makes a small circle around the actual pole as Earth rotates.
What kind of star is Polaris?
First off, let's get a common misconception out of the way. Polaris, the current North Star, is not the brightest star in the night sky. It's the brightest star in its particular constellation, but there are over 40 stars in the sky that are brighter than Polaris. The exact rank changes periodically as more accurate instruments are used to measure star brightness, but Polaris is usually ranked between 45 and 50 in the lists of brightest stars. In addition to this, Polaris is a type of variable star - specifically, a Population I Cepheid Variable - which means that its actual brightness varies.
Polaris is also called Alpha Ursae Minoris, because it's the brightest star in Ursa Minor, the Little Bear (also known as the Little Dipper). It is actually a multiple star system made up of at least three stars. The largest star in the system is called simply Polaris A, and is a supergiant that has about six times the mass of the sun. The other stars in the Polaris system are much smaller dwarf stars.
Where can I find the North Star?
Polaris is the star at the end of the handle of the Little Dipper, or the tip of the tail of Ursa Minor, the Little Bear. There's a trick you can do with the Big Dipper to find it. Find the Big Dipper, then go to the stars at the end of the Dipper's bowl - Merak and Dubhe, also known as "the pointer stars" - draw a line between those stars, and then continue that line. The line should take you right to the North Star. You'll always find the North Star in the northern sky.
Why is the North Star special?
The significance of the North Star has to do with location rather than brightness.
Throughout much of history, humans didn't have GPS or road signs to help them find their way around. They often used the sun and the stars for navigation, especially in areas like oceans and deserts, where there aren't many reference points. Since you will always find the North Star in the northern sky, you can use it to find north, even in the absence of landmarks. Once you've found north, you can figure out south, east, and west as well. When slaves were escaping the south in the 19th century, they often used the North Star and the Big Dipper (which they called the Drinking Gourd) to help them find their way along the Underground Railroad.
Since the North Star appears higher in the sky the further north you go (and lower the further south you go), navigators have also been able to use it to help find their latitude. Ancient mariners knew the North Star's altitude - the angle between an object, an observer, and the horizon - from their home base, which made it easier to find their way home after a voyage.
Now, if you ever get lost at night when the skies are clear and your GPS isn't working, you can use the North Star to figure out your directions and maybe even get a general idea about your location.