What is the primary difference between a double star and a binary star?
A double star is defined by observation from Earth, while a binary star is defined by a physical, gravitational relationship.
The distinction lies in the nature of the relationship between the two celestial bodies. A double star, or visual double, is a classification based solely on perspective; it describes any pair of stars that appear close together from our vantage point, regardless of their actual distance from one another or their physical connection. In contrast, a binary star system refers to two stars that are gravitationally bound to each other, engaging in an orbital dance around a shared center of mass. This physical connection dictates their behavior and evolution, distinguishing them from the mere coincidence of position found in optical doubles.
