Figure 10-11 A Binary Star System About one-third of the objects we see as “stars” in our region of the Milky Way Galaxy are actually double stars. Mizar in Ursa Major is a binary system with stars separated by only about 0.01 arcsec. The images and plots show the relative positions of the two stars over nearly half of their orbital period. The orbital motion of the two binary stars around each other is evident. Either star can be considered fixed in making such plots. (Technically, this pair of stars is Mizar A and its dimmer companion. These two are bound to another binary pair, Mizar B and its dimmer companion.)