- See under double star.
- two stars that appear as one if not viewed through a telescope with adequate magnification, such as two stars that are separated by a great distance but are nearly in line with each other and an observer (optical double star), or those that are relatively close together and comprise a single physical system (physical double star).
- two stars, appearing close together when viewed through a telescope; either physically associated (binary star) or not associated (optical double star)See also binary star, optical double star
- two stars that appear close together when viewed through a telescope but are not physically associated and are often separated by a great distanceCompare binary star
- See binary star.