Rubin was an American astronomer who discovered dark matter. Dark matter is a material in the universe that does not reflect light. She and W. Kent Ford found that the stars closest to the center of the galaxy and the stars farthest from the center of the galaxy moved at the same rate.  Their findings said that mass astronomers could see only 10 percent of the galaxy's total mass. This makes dark matter invisible. Rubin joined the council of American Women in Science in 1984 to promote women in astronomy. 