The Stellar Systems Family
The Family of stellar systems ranges from binary stars to globular clusters with millions of stars. Binary stars are two stars that are gravitationally bound in a mutual orbit. They are sometimes also termed double stars, but that designation may also include stars that only appear close together in the sky. It is estimated that at least 80% of all stars are members of binary or multiple star systems. Strictly speaking, binaries are multiple stars (S 32), but in common astronomical usage multiple stars are systems with three or more stars.