By Deborah Byrd
Thursday, Oct. 8, 2009
At this time of year, the most famous star pattern visible from this hemisphere — the Big Dipper — is low in the north during the evening hours. It’s tough to spot the Dipper in the evening at this time of year, especially in the southern states, although you’ll see it before dawn around now, ascending in the northeast.
The distances of the stars in the Dipper reveal something interesting about them: five of these seven stars have a physical relationship in space. That’s not always true of patterns on our sky’s dome. Most star patterns are made up of unrelated stars at vastly different distances.
But Merak, Mizar, Alioth, Megrez and Phecda are part of a single star grouping. They probably were born together from a single cloud of gas and dust, and they’re still moving together as a family.
The other two stars in the Dipper — Dubhe and Alkaid — are unrelated to each other and to the other five. They are moving in an entirely different direction. Thus millions of years from now the Big Dipper will have lost its familiar Dipper-like shape.
Here are the star distances to the Dipper’s stars:
- Alkaid 101 light-years
- Mizar 78 light-years
- Alioth 81 light-years
- Megrez 81 light-years
- Phecda 84 light-years
- Dubhe 124 light-years
- Merak 79 light-years