Stop #5 – The Big Dipper and the North Star

The Big Dipper and the North Star

Perhaps the most famous asterism in the sky is The Big Dipper. It’s composed of the seven brightest stars of the constellation Ursa Major (The Great Bear); three make up the handle (Alkaid, Mizar, Alioth), and the other four make up the bowl-part (Megrez, Phecda, Merak, and Dubhe).

The Big Dipper

The Big Dipper

The Big Dipper is on the other side of the sky from Sirius and Orion- turn around and look towards the north.

Polaris: The North Star
Polaris can be thought of as the star at the North Pole of the Celestial Sphere. If you were at the North Pole, it would always be straight-up above you. If you were at the South Pole, you would never be able to see it. Since North America and Europe are about mid-way up between the equator and the north pole, Polaris appears to us about mid-way up the sky, between the horizon and straight-up.

It’s not the brightest star in the sky, but ranking at 46th brightest in the sky, the North Star is not that hard to spot, either- especially if you can find the Big Dipper.

The last two stars in the Big Dipper scoop out to point at the North Star. Follow them about 5 lengths out of the spoon to find a relatively bright star, sitting almost alone in the north.

The North Star has one unique property- it will always appear at exactly the same point in the sky; it never moves*. All the other stars will appear to rotate around it, making one great big circular trip every day.

*As the entire celestial sphere’s tilt-angle appears to change slightly throughout the seasons, technically the North Star will appear to move slightly up the sky, then down the sky, throughout the year, but day-to-day, it’ll always appear in the same spot.