Tombstone Sky
Dark-Site Observatory

Polar Region

The "polar region" is that area of sky immediately around the North Star. This star moves so little in the sky, year around, that it's almost unnoticeable. If you draw a line from that star right through the center of Earth and out the other side, the entire sky rotates, like a big globe, around that axis - just like Earth rotates around the north pole. In other words, all stars are always the same distance from the North Star, year around. Depending on that distance, that star may or may not be visible, depending on what month of the year it is.

If you draw a circle around the North Star, with a radius equal to the distance between the North Star and straight down to the horizon to the north, you see that no stars in this circle ever set. They are always in the sky, circling the North Star, taking one year to complete one rotation.

Strictly speaking, this circle defines a "polar region", but that's a little too strict for practical use. Although the North Star never moves in the sky from your present location, it does move as you move north and south. Specifically, the North Star is always the same height above the horizon (in degrees) as your current latitude. So, if you're currently at latitude 40°N, the North Star would be 40° above the north horizon.

(However - you can move east and west all you like, and the North Star will be in the same place in the sky.)

Since our strict polar region would become smaller and smaller the farther south we go, we define a more general definition for Polar Region, and even that's not exact - it seems to depend on the author - but there are some stars and constellations which everyone pretty much agrees are in this region.

You need to be familiar with, in addition to the North Star, the Big Dipper and Cassiopeia. Even as far south as Tombstone, one of the two is always visible in the sky, and most months, both are visible. If you live up in Montana, for example, both will be visible year around.

Now that you can find the North Star with no trouble, take the time for the constellation it's part of - the Little Dipper.

The other polar constellation is the Dragon, which we pick up in May Monthly Pick.