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visual binary:see binary starbinary star
or binary system,
pair of stars that are held together by their mutual gravitational attraction and revolve about their common center of mass. In 1650 Riccioli made the first binary system discovery, that of the middle star in the Big Dipper's handle, Zeta
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visual binaryA binary star, such as Sirius or Gamma Centauri, whose components are sufficiently far apart to be seen separately, either with the naked eye or with a telescope. In most cases the components differ in brightness: the brighter star is designated the primary and the other is the companion. Observations over a period of time reveal the apparent orbit of the companion relative to the primary, from which the true orbit is derived by adjusting for the inclination of the orbital plane. If the distance is known the total mass of the binary can be obtained from Kepler's third law:
Visual binaries generally have long orbital periods and in some cases the period is too long for any orbital motion to be detected. Such pairs are called common proper motion stars because, unlike optical double stars, they appear to stay together as they move across the sky.