Spectroscopy at Lowell
Slipher joined Lowell Observatory after graduating from Indiana University in 1901. He learned spectrograph techniques for planetary research, extended them to stars and spiral nebulae, and later helped direct the observatory.
Measuring spiral nebulae
In late 1912 he measured a large approaching velocity for Andromeda from Doppler shifts in spectra exposed over several nights. By 1914 he had velocities for fifteen spiral nebulae, most redshifted and some blueshifted. Their nature and distances were still disputed; the measurements subsequently became important evidence in work on cosmic expansion.
References: [2]
Organising the Pluto search
After Percival Lowell’s death, Slipher helped revive the search for an outer planet and employed Clyde Tombaugh. Tombaugh identified Pluto on photographs in 1930; Slipher provided organisational, staffing and financial support for the search.
References: [2]