Optical doubles are pairs of stars that appear close together in the sky but are not physically related. They are called "optical" because their proximity is a result of their alignment from our viewpoint on Earth, rather than a true gravitational connection. These stars can be at vastly different distances from us. Astronomers often study optical doubles to better understand stellar properties and distances. While they may seem like a binary system, only one star may be part of a binary system, such as a binary star, while the other is a solitary star. This distinction is important for accurate astronomical measurements.