The Night Sky: Ursa Minor (The Little Dipper) and Polaris

Attached is my picture of Ursa Minor, Latin for ‘Smaller Bear.’ Although it depicts a small Bear, the shape of Ursa Minor also resembles a ladle, so Ursa Minor is widely known as The Little Dipper. The stars of the Little Dipper are not very bright, so it can be hard to find in the northern sky unless you are in a dark location.
 
The most famous star in the Little Dipper, and in the entire sky, is Polaris. Polaris just happens to be located near the axis of the Earth's rotation, so everything in the sky rotates around Polaris. Polaris remains almost stationary in the North as the Earth rotates, thus it is known as The North Star.  Because Polaris remains north it was invaluable in celestial navigation. Even now in the age of Global Positioning, it sometimes helps me find my way while driving.
 
See my Earth Rotation picture to help visualize stars creating arcs around Polaris as the Earth rotates. The star trails in the picture represent almost 30 minutes of Earth rotation.Polaris and the axis of rotation are located near the upper left of the picture.

Polaris is 425 light-years from Earth, and is part of a multiple star system. Polaris has four companion stars. The brightest companion star is not seen in the picture and can’t be seen with the unaided eye. It can be found very near Polaris using almost any telescope.

Polaris is a Cepheid variable star. Cepheid variable stars are important because their true brightness is directly related to variations in their light output. This Period-Luminosity relationship was discovered by Henrietta Swan Leavitt in 1908. Because of her discovery Cepheid variable stars became tools to measure distances in space. This distance information helped reveal very important facts like the shape of our Milky Way Galaxy, our Sun’s position in the Milky Way, and even the distances to other galaxies.

So a big thanks to Henrietta Swan Leavitt and to Polaris.

Clear Skies!