Finding Polaris, the North Star

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This page is a short explanation of how to find Polaris, the "North Star". This is not something you would do for the pleasure of observation. Polaris is just a star, not especially interesting to look at (although it is a close binary star, so is interesting if you like observing binaries).

Instead, Polaris is a very useful reference for finding the North Celestial Pole when polar-aligning an equatorial mount. It is within about 1 degree of the North Celestial Pole -- close enough that, for most purposes, aligning the equatorial mount to Polaris is good enough.

General Sense of Polaris' Location

After some practice, you will be able to find Polaris easily and automatically just from having a general sense of where it should be. It has the advantage, of course, that it never moves in the sky; so once you know where it is relative to a favourite observing location, it will be in that same spot every time you need it.

To find Polaris, look due North, and look up in the sky at an elevation that is equal to your latitude.

Let's do that last part again. Your latitude, which you can look up in an Atlas or on the Internet, is measured in degrees North of the equator. I live in Ottawa, Canada, at latitude 45 degrees. Phoenix, Arizona is about 33 degrees latitude, while Iqaluit in Nunavut Territory, Canada, is about 64 degrees North.

By definition, the elevation of Polaris above the horizon is exactly equal to your latitude. So, in Ottawa, 45 degrees, Polaris is exactly halfway between the horizon and "straight up". In Phoenix it would be lower; go up to 45 degrees and then down about a third back toward the horizon. In Iqaluit, go up to 45 degrees and then up about another third toward straight up.

Once you are looking due North and up the correct amount, Polaris is the brightest star in that general area of the sky. That part of the sky is not very crowded with bright stars, so Polaris stands out nicely.

Finding it with Constellations

To find Polaris more accurately, we can use a couple of constellations as pointers.

(Note: we are actually using Asterisms, not Constellations. For example, the Big Dipper is an asterism: an unofficial picture in the sky based on modern and popular symbols; the constellation containing the Big Dipper is Ursa Major, the Great Bear, and it is quite a bit larger and involves more stars.)

Take a moment and remember when you last saw a "dipper" - an old-fashioned metal ladle used to dip water out of a pail. dipper.gif
Look in the Northern part of the sky for "the Big Dipper", a group of seven stars shaped like a dipper, with a square cup and a gracefully curved handle. The seven stars are all bright and the shape is very easy to recognize and find. big-dipper-rsu.jpg
Although the Big Dipper is visible all year, it does move around the sky, so it may appear upside down, big-dipper-usd.jpg
or it may be standing on one end or the other, depending on the time of year. big-dipper-end.jpg
Imagine a line drawn across the outermost two stars in the "cup" of the dipper, and extend this line about 5 times the distance between those two stars.

The imaginary line points almost exactly at Polaris.

Polaris-found.jpg

You can confirm this is Polaris: it is the star at the end of the handle of "the Little Dipper", another "dipper" asterism. The Little Dipper is harder to see because all its stars are dim, and it is not as good artistically - the handle curves the wrong way.

The bright star at the end of the handle of the Little Dipper, which is pointed to by the two stars at the end of the cup of the Big Dipper, is Polaris, the North Star.

Misconceptions

There's a popular misconception or two about this star. For example, in the great Gerry Rafferty song, we have the line

You've been as constant as the Northern Star, the brightest light that shines

Two problems here.

  1. First, it's not the brightest star in the sky. Not even close - it is the 48th brightest.
  2. Second, and I think more interesting: it's also not constant. It's a variable star (specifically, a Cepheid variable) that changes brightness by a tiny amount over a period of about 4 days. It is, however, the brightest Cepheid, still an interesting distinction. I think that's just cool.



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