Capella - Alpha Aurigae
The Capella star is 42 light years away from the Earth in the constellation of Auriga. It may appear as one star but it is actually a pair of binary stars that are right next to each other. A binary star is two stars that orbit around each other. Since there are two stars named Capella, astronomers had to name them Capella A and Capella B. The two stars orbit each other every 100 days at a distance of around 62,000 miles.Capella A and Capella B are both post main sequence stars, this means that they have used up all of their hydrogen in their core and have expanded to about 5 times their original size.
Both stars are G class giants, Capella A's mass is 2.7 times bigger than the sun while Capella B's mass is 2.5 times greater than the sun. Capella A's luminosity is 80 times greater than the sun while Capella B's luminosity is 75 times more powerful than the sun. Capella A has a temperature of 4900C while Capella B has a temperature of 5700C. Capella A's diameter is 10.4 million miles - 12 x Sun, Capella B's diameter is 7.8 million miles - 9 x Earth Both of the stars will become red giants over the next few million years, expanding to many hundreds of times their original size.