In an article published in the October 1977 issue of Deep Sky Monthly, I wrote that Jean Baptiste Riccioli discovered the first double star, Mizar (Zeta [ζ] Ursae Majoris), in 1646. I based my information on what commonly appeared in astronomy texts. How odd, I thought, that nearly 4 decades should pass from the time of the telescope’s invention to the discovery of the first double star.
Glenn Chaple’s Observing Basics: Double the observing fun
August 2009: Split some binary stars or measure an eclipsing binary's change in brightness.