1875-1969

American astronomer who contributed to spiral nebulae theory. Earning a doctorate from Indiana University, Slipher measured planets' rotation periods at the Lowell Observatory. Slipher's most important research concerned the spectrographic study of spiral nebulae. He examined data to determine if spiral nebulae resembled the Earth's solar system. Slipher measured spiral nebulae's velocities, noting that they were moving away from Earth. This information supported other astronomers' theory of an expanding universe. Slipher also served as director of the Lowell Observatory.