What is the difference conceptually between an optical double star and a visual binary star?

Answer 1

A visual binary is a true binary (gravitationally bound) pair of stars, in which the two stars can be seen to be separate through a telescope. This is to distinguish it from a spectroscopic binary, in which the presence of two stars can be detected only by the doppler shifts in their spectral lines.

An optical double is a pair of stars that are actually unrelated, but appear close together from our perspective.

Answer 2

Optical Double Star

Answer 3

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They are not the same thing. Binary stars are actual physical systems, where the two stars revolve around each other. Double stars include binaries, but also include visual doubles, where two stars happen to lie along the same line of sight, but are not physically close to each other and don't form a physical system. Variable stars vary in brightness. Some are close binary stars where one star eclipses the other, but most are intrinsic variables, where the star itself varies in brightness because of astrophysical processes going on in its atmosphere.

Answer 4

An optical double is simply two stars that appear to be very close to each other from our perspective, but they are actually not near each other in reality. It's like if you put your finger right in front of your eye and put a finger from your other hand as far away from your face as you can but right next to your close finger visually. They look like they're next to each other but they arent.

A visual binary is where the stars are actually next to each other, and are in fact gravitationally bound to each other.