Not all stars travel alone, like the sun. Many are paired, the two members revolving around each other like the ends of a spinning dumbbell. Such bright stars as Capella, Spica, Castor, Mizar (a Big Dipper star) and Algol (the "Demon Star") are binaries (doubles). Some stars occur in groups of more than two. Astronomers estimate that one-fourth or more of all the stars in the sky are doubles or multiples. Last week astronomers heard of a pair of stellar Siamese twins.
Sometimes the stars of a binary are so close together that even...
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