Castor (star)
Castor is a multiple star system made up of six different stars; there are three visual stars, all of which are spectroscopic binaries. Appearing as a single star to the naked eye, Castor was first recorded as a double star in 1718 by James Pound, but it may have been changed into at least two sources of light by Cassini as early as 1678. The separation between the binary systems Castor A and Castor B has increased from about 2″ (2 arcseconds of angular measurement) in 1970 to about 6″ in 2017.