and the sample in our own solar system is too small to draw any general conclusions. We have great gaps in our knowledge of stellar binaries, but we do have large amounts of data nonetheless--binary stars have been of great interest to astronomers since the invention of the telescope, and even though thousands have been catalogued, no doubt observational difficulties and selection effects have been instrmental in keeping our knowledge of them limited. Still, binary stars were our first confirmation of Keplerian motion and Newton's Laws holding outside our solar system, so they are a favorite among astronomers. For the amateur, they provide contrasting-color pairs of great visual beauty, and an opportunity to add to scientific observations since they are well suited to amateur equipment.

Many stars in the heavens appear "double", even to the human eye, and although some are accidental or chance line-of sight alignments, many are actually gravitationally connected pairs. Some binaries are extremely close, even in physical contact, and can only be detected by the variation in brightnerss as they eclipse each other (eclipsing binaries). Others can only be deteced spectroscopically, their spectra are the superimposed spectra of two or more stars. Still others can actually be observed to rotate about one another, with periods raising from hours, to centuries, depending on how close the stars are to each other. Others are so far apart they show no evidence of gravitational connection, and are only suspected binaries because of a shared proper motion and radial velocity.

Our nearest stellar neighbor, Alpha Centauri, is a triple star system, two fairly close bright companions orbiting one another at distances comparable to the scale of our own system (they are easily resolved in amateur 'scopes) And a third, a dim red dwarf Proxima, in orbit around the other two in a very elongated eliptical orbit. Look up the Wikipedia entry on this trio. Its a fascinating system.