How did William Herschel show that double stars can orbit each other?

William Herschel observed that double stars—pairs of stars that appear close together in the sky—do not occur by chance due to random scattering in space. Instead, he concluded that these pairs are physically associated and actually revolve about each other.1

While Herschel cataloged 848 such systems, his work in this area was part of a broader effort to understand the structure of the heavens. His son, John Herschel, later continued this research, as the orbital motions of these pairs offered a vital opportunity to investigate the gravitational forces operating throughout the universe.12