Optical binary

This page is about a novel by Robert Heinlein. For other uses, see double star (disambiguation). Double Star is a science fiction novel by Robert A. Heinlein, first serialized in Astounding Science Fiction (February, March, April 1956) and published in hardcover the same year. At the 1957 Worldcon it received the Hugo Award for Best Novel of the previous year.
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This topic is about the astronomical phenomenon. For other uses, see double star (disambiguation). A double star is when two stars appear close to each other as seen from Earth.There are two kinds of double star: visual binaries and optical binaries. Visual binaries are considered to be a true binary star system and lie close enough together in space to interact gravitationally such that the stars orbit each other. Optical binaries (aka optical doubles), on the other hand, are two stars that only appear to be close together, and are actually separated by a great distance in space and are not gravitationally bound to each other.
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A pair of stars which happen to lie close to one another on the celestial sphere because of a chance alignment. They are not physically associated with one another and probably exist and vastly different distances. Optical binaries are also known as visual binaries . See binary star .