two stars that lie very close to, and often orbit, each other. Line-of-sight doubles are a consequence of perspective and aren't physically related. Most stars, however, are multiples gravitationally bound together. Usually the stars orbit so closely that they appear as a single point of light even when viewed through professional telescopes.
Two stars which are close to each other in the sky. Includes optical doubles and binary stars.
a pair of stars which appear to be very close together
Two stars that appear near each other in the sky. Their apparent closeness may be due to chance alignment—with one star, in fact, far beyond the other—or they may be in orbit around a common center of gravity, in which case they form a binary star.
A group of two (or more) stars that appear to the naked eye to be one, but can be separated into two with a powerful enough instrument.
A system containing two or more stars. In many double star systems, the stars are not actually physicall close to eachother, they only appear to be beacuse of the way we view the sky. True double stars are called binary stars. See also: binary star, of course.
A grouping of two stars. This grouping can be apparent, where the stars seem close together, or physical, such as a binary system.
Two or more stars that appear very close in position. True double stars are in orbit about one another, while optical double stars simply appear close together as seen from the Earth.
A system of two stars that revolve around each other under their mutual gravitation.
A double star is two stars that appear close to one another in the sky. Some are true binaries (two stars that revolve around one another); others just appear together from the Earth because they are both in the same line-of-sight.
