optical double

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optical double:

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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optical double

1. See double star.
2. See double galaxy.
References in periodicals archive ?
Yet all of the included pictures show the potential for dozens of other optical doubles (especially the illustration for 16 and 17 Draconis).
"Matt Wedel replies: If there's a standard designation system for optical doubles, it's news to me.
Astronomers call the true couples binary stars and the chance alignments optical doubles.
In an optical double, one star lies far beyond the other; their appearance of closeness is simply a line-of-sight coincidence.
In contrast, optical doubles are physically unrelated but coincidentally aligned along our line of sight.
The whole stretch from Kappa to Lambda is packed with neat little asterisms and optical doubles.
Tau2 and Tau4 Serpentis are wide optical doubles that seem to mirror each other across an imaginary line extending southwest from Tau5 Serpentis.
"Double stars" include both binaries and optical doubles, pairs that merely look close together on the sky but whose stars are at different distances and physically unrelated.
This lovely naked-eye optical double adds to the overall fascination of the district around Antares and the head of Scorpius, as shown at left.
Visual observers will still be needed, but for the highest scientific value they will need to perform specific observations--watching for an outburst of a rare class of star, making time-critical observations when robotic facilities might be clouded out, measuring the brightness of close optical doubles, and so on.
These are called optical doubles. But many are genuine binary stars: pairs orbiting in each other's gravitational grasp.
Optical doubles are at different distances, too far apart to be physically related; they appear close only because they happen to lie very nearly in the same line of sight as viewed from Earth.