Canadianengineer and astronomer. He designed a new spectrograph for measuring stellar radial velocities, which was used from 1918 with the Dominion Astrophysical Observatory's 72-inch (1.85-m) reflector, a telescope largely of his design and now named after him. The numerous radial velocity measurements revealed many spectroscopic binaries, including Plaskett's Star, as well as the rotation of the Galaxy and the location of its centre. Plaskett also showed that lines of calcium in stellar spectra came from interstellar matter. His son, Harry Hemley Plaskett (1893–1980), was an accomplished solar spectroscopist.
Subjects: Astronomy and Astrophysics.