Vesto Slipher

Vesto Slipher (1875–1969) was an American astronomer whose spectroscopic measurements revealed large velocities among spiral nebulae, later identified as galaxies. His redshift data helped establish evidence for cosmic expansion.

Galaxy redshift: The displacement of a galaxy’s spectral lines toward longer wavelengths, commonly associated with recession from an observer. Slipher measured these spectral shifts to infer the velocities of spiral nebulae.
Spectroscopy: The study of how matter interacts with electromagnetic radiation, often by analyzing spectra. Slipher used spectroscopy to measure the displacement of nebular spectral lines.
Lowell Observatory: An astronomical research institution founded by Percival Lowell in Flagstaff, Arizona, in 1894. Slipher spent his career there and made his major nebular observations with its telescopes.
Willem de Sitter: A Dutch theoretical physicist and astronomer who developed influential solutions to Einstein’s equations of general relativity. De Sitter interpreted Slipher’s nebular velocities in relation to relativistic cosmology.
M51: A pair of interacting galaxies in Canes Venatici, also known as the Whirlpool Galaxy and its companion NGC 5195. Slipher obtained an early spectrum of this spiral nebula while developing his measurement method.
Edwin Hubble: An American astronomer who established the distance scale for galaxies and published evidence linking distance with recession speed. Hubble combined distance estimates with Slipher’s velocity measurements to reveal a relation between distance and recession.
Doppler effect: The change in a wave’s observed frequency caused by relative motion between its source and observer. The Doppler interpretation connected Slipher’s spectral shifts to nebulae moving toward or away from Earth.
Percival Lowell: An American astronomer who founded Lowell Observatory and promoted the search for canals on Mars. Lowell hired Slipher and directed the observatory where his spectroscopy program developed.
Georges Lemaître: A Belgian priest, physicist, and astronomer who derived an expanding-universe model from general relativity. Lemaître connected cosmic expansion with astronomical velocity and distance evidence, including Slipher’s data.
M104: A galaxy in Virgo known as the Sombrero Galaxy because of its bright central bulge and prominent dust lane. Its spectrum was among the early spiral-nebula observations associated with Slipher’s program.

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