Plaskett, John Stanley (1865–1941)

Canadian astronomer and engineer. He discovered many new binary stars, including Plaskett's Twins, previously thought to be a single, massive star. He also carried out research into stellar radial velocities.

Plaskett was born at Hickson near Woodstock, Ontario, and trained as a mechanic before studying at Toronto. From 1903 he was in charge of astrophysical work at the new Dominion Observatory in Ottawa. He was the first director of the Dominion Astrophysical Observatory in Victoria 1917–35, and designed its 1.8-m/72-in reflector telescope 1918. He then supervised the construction of a 205-cm/82-in mirror for the MacDonald Observatory at the University of Texas.

He worked mainly on radial velocities and spectroscopic binaries. His work on the radial velocities of galactic stars enabled him to confirm 1930 the contemporary discovery of the rotation of the Galaxy and to indicate the probable location of its gravitational centre. This led to a study of the motion and distribution of galactic interstellar matter, particularly calcium.

His elder son, H H Plaskett, who also worked at Victoria, later became professor of astronomy at Oxford.