Vera Rubin (July 23, 1928- ) is an American astronomer responsible for pioneering work on galaxy rotation rates. Famous for uncovering the differences between the predicted angular motion of galaxies and the observed motion using galactic rotation curves, she noted that, according to calculations of the data gathered from visible matter, galaxies should have been moving at much slower of a pace. This discrepancy became the evidence for a hypothetical invisible matter, better known by its alternate name of “dark matter.” (via)