Vesto Slipher

Vesto Melvin Slipher (1875-1969) was an American astronomer who spent most of his career at Lowell Observatory in Flagstaff, Arizona. Beginning around 1912, Slipher used spectroscopy to measure the radial velocities of spiral nebulae, later understood to be separate galaxies, and found that most of them showed a redshift in their light, meaning they were receding from Earth at high speed. He was the first astronomer to make such measurements, and his data on galactic redshifts and velocities, gathered over more than a decade, provided the essential observational foundation that Edwin Hubble and others later used to establish that the universe is expanding. Slipher also served for many years as director of Lowell Observatory, overseeing the search that led to the 1930 discovery of Pluto by Clyde Tombaugh. His early spectroscopic measurements remain a foundational contribution to twentieth-century cosmology.