Photograph by Mark Godfrey, courtesy of AIP Emilio Segrè Visual Archives, Gift of Vera Rubin · Attribution

Rubin's measurements of how fast stars orbit within galaxies didn't match what gravity from visible matter alone could explain — the outer stars were moving too fast, as if something invisible were holding the galaxy together. That discrepancy became one of the central pieces of evidence for dark matter. She spent her career at the Carnegie Institution, won the Gold Medal of the Royal Astronomical Society and the National Medal of Science, and mentored younger women into a field that had few of them; the physicist Lisa Randall and others have argued she was overlooked for a Nobel Prize she never received. The Vera C. Rubin Observatory in Chile now carries her name.