One of the great lingering mysteries of the universe is dark matter. Scientists are not sure what it is, but most believe it's out there, and in abundance. The astronomer who finally convinced many of them was Vera Rubin. When Rubin died in 2016, she was regarded as one of the most influential astronomers of her era. Her research on the rotation of spiral galaxies was groundbreaking, and her observations contributed significantly to the confirmation of dark matter, a most notable achievement.