optical double
(apparent binary)
(double star where the two are not gravitationally bound)
The meaning of term optical double (or apparent binary)
is a double star (two stars close together in the celestial sphere)
that don't constitute a binary star (two stars co-orbiting)
but because of chance alignment of the two stars with us.
They are "optical" in that they look like a binary.
The term physical double is sometimes used for an actual binary star.
(star type,double stars)
Further reading:
https://en.wikipedia.org/wiki/Optical_double
https://en.wiktionary.org/wiki/optical_double
https://www.oxfordreference.com/display/10.1093/oi/authority.20110803100252164
Referenced by pages:
Aitken Double Star Catalogue (ADS)
binary star
blended spectra
double star
double star designation
Index