Big Dipper
Written by Jerry Coffey
The Big Dipper. Image credit: Jerry Lodriguss
Five of the stars of the Big Dipper are the core of the Ursa Major Moving Group. Dubhe and Alkaid are not part of the group and are moving in the opposite direction. When compared to the central five, they are moving down and to the right in the map. This will slowly change the Dipper's shape, with the bowl opening up and the handle becoming more bent. In 50,000 years the Dipper will no longer exist as we know it, but be re-formed into a new asterism facing the opposite way. The stars Alkaid to Phecda will then constitute the bowl, while Phecda, Merak, and Dubhe will be the handle.
The stars that make up the Big Dipper are easy to find. They also serve as good guideposts to other stars. Polaris is found by imagining a line from Merak to Dubhe and then extending it for five times the distance between the two Pointers. Extending a line from Megrez to Phecda, on the inside of the bowl, will lead you to Regulus and Alphard. If you pull out your telescope and follow a line from Phecda to Megrez and continuing on for the same distance again, you will find the Hubble Deep Field.
In North America the asterism is known as the Big Dipper because the major stars can be seen to follow the rough outline of a large ladle or dipper. This figuration appears to be derived originally from Africa, where it was sometimes seen as a drinking gourd. In the 19th century, runaway slaves would follow the drinking gourd to the north and freedom.
If you follow this link, you will find a good article about the Big Dipper. Here on Universe Today we have a great article about the the Ursa Major constellation. Astronomy Cast offers a good episode about the vast topic of all of the constellations.
Filed under: Astronomy
Tags: Alioth, Alkaid, Big Dipper, Dubhe, Megrex, Merak, Mizar, Phecda, Ursa Major
