Binary Star
a star which, closely examined by the telescope, is found to consist of two stars revolving around their common center of gravity. In some cases they are colored differently from each other. In 1803 Sir William Herschel discovered that Gamma Leonis, Epsilon Bootis, Zeta Herculis, Delta Serpentis, and Gamma Virginis are revolving double stars, and others, including Castor, have since been added to the list, a large proportion of the later discoveries having been made by Sherburne W. Burnham, Professor of Practical Astronomy in the University of Chicago (1900). The period of revolution in various cases has been determined. It is found to vary from 26 to more than 1,200 years.