Binary stars are not the same as line-of-sight "optical double stars", which look close together but are not connected by gravity. Optical double stars may actually be far apart in space, but binary stars are quite close together. The first person to discover and prove true binary stars was the Anglo-German astronomer William Herschel. He published the first catalogue of binary stars, and his son John Herschel found several thousand more and updated the catalogue. John Michell first suggested that double stars might be physically attached to each other when he argued in 1767 that the probability that a double star was due to a chance alignment was small. William Herschel began observing double stars in 1779 and soon after that he published catalogs of about 700 double stars.