Optical Double
Related Category: Astronomy: General
see binary star.
More on Optical Double ...
optical double
Two stars at different distances that lie along nearly the same line of sight and thus appear close together
optics ...
Optical doubles are distinguished from binary stars by observing them for a long period of time, usually years.
optical double - (n.)
A pair of stars that appear extremely close together in the sky even though they are at different distances from us and are not physically linked.
orbital - (n.) ...
optical double star (NASA SP-7, 1965) Two stars in nearly the same line of sight but differing greatly in distance from the observer, as distinguished from a physical double star. optical haze (NASA SP-7, 1965) = terrestrial scintillation.
Another optical double is tau Leo; the 7th mag campanion of this orange 5th mag star can be seen in binoculars.
The binary gamma Leo, called Algieba (the lion's mane), is a magnificent pair, which compenents consists of a orange-red giant of 2.
6 minutes of arc, the naked eye "double star" Algedi (toward the upper right) is actually an "optical double" that consists of two unrelated line- of-sight stars, Alpha-1 Capricorni at right, Alpha-2 at left.
Pairs of stars like Mizar and Alcor that appear to be together (like this) are called "optical doubles".
He continued to work on double stars, and was the first to discover that most double stars are not mere optical doubles as had been supposed previously, but are true binary stars, ...
Since Beta Centauri is about 300 light years away, they will be an optical double. Now the two stars look like two eyes, the right one (Beta) distinctly blue. They are called the 'pointer stars' since they point to the Southern Cross to the west.
Note that while gammaA and gammaB are labelled as binary components, these stars only form an optical double. The two theta stars are also not gravitationally bound to each other; on the other hand mu1 and mu2 do form a binary system (see below).
[5795] delta Ophiuchi (Yed Prior), a red giant 170 light-years distant, and [5798] epsilon Ophiuchi (Yed Posterior), a class G giant 108 light-years distant, form a naked eye optical double and mark Ophiuchus' left arm. (Yed means "hand" in Arabic.) ...
However, not all stars apparently close together are gravitationally connected, they could be actually at different distances from the observer. Such stars are called optical doubles, e.g.
Occasionally, two unrelated stars just happen to lie close together in the sky, even though they are actually widely separated. These optical doubles are just chance superpositions and carry no useful information about stellar properties.
or radial velocities, or if parallax measurements reveal its two components to be at sufficiently different distances from the Earth. Most known double stars have not yet been determined to be either bound binary star systems or optical doubles.
A double star is not necessarily a binary, a two-star system revolving about a common center, but may be an optical double, two unconnected stars in the same line of sight.
 See also: Double star, Star, Telescope, Light, Constellation
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