"Like Bradley, Herschel made an unexpected discovery in searching for parallax. He selected for observation stars close to each other in the sky, following the guidance of Galileo. Although Herschel failed to find parallax, he did find that in some cases the stars he observed appeared to be in relative motion around their common center of gravity. They were clearly "binary stars," bound by gravity to orbit one another. It is now realized that almost half of all stars can be found in binary systems."