A pioneer in the study of the motions of galaxies, Vera Rubin (1928-) helped show that most spiral galaxies contain about ten times more mass than can be seen. She observed stars revolving around the centers of galaxies and found that their velocities stayed pretty much constant regardless of their distance from the galaxyís center. This stood in marked contrast to the situation in the solar system, where the speeds of the orbiting planets drop dramatically the farther they are from the Sun. The observations only make sense if a vast halo of dark matter surrounds the galaxies, one of the first indications that there is more to the universe than meets the eye. In 1965, Rubin became the first woman to observe at Palomar Observatory.