Humason, Milton Lasell (1891-1972)

US astronomer who carried out a spectroscopic study of distant galaxies, determining their velocities from their red shift.

Humason, born in Dodge Centre, Minnesota, dropped out of school at 14 to hang around Mount Wilson Observatory, California. For a while he was a mule driver for the pack trains that carried construction materials to the observatory from the Sierra Madre. In 1917 he joined the observatory staff as a caretaker, but was quickly promoted, becoming assistant astronomer 1919. From 1954 he was astronomer at the Mount Wilson and Palomar Observatories.

At Mount Wilson Observatory, Humason took part in an extensive study of the properties of galaxies, initiated by Edwin Hubble in 1928. The work consisted of making a series of systematic spectroscopic observations to test and extend the relationship that Hubble had found between the red shifts and the apparent magnitudes of galaxies. But because of the low surface brightness of galaxies there were severe technical difficulties. Humason developed the technique and made most of the exposures and plate measurements. The velocities of 620 galaxies were measured, and the results, published in 1956, still represent the majority of known values of radial velocities for normal galaxies.