Plaskett , John Stanley

(1865–1941) Canadian astronomer

Plaskett, who was born at Woodstock, Ontario, was initially trained as a mechanic and began work as such for the physics department of the University of Toronto. He eventually graduated from there in physics and mathematics in 1899. When he moved, in 1903, to the Dominion Observatory in Ottawa it was as mechanical superintendent and not as an astronomer. He gradually moved into astronomy, however, and in 1918 became director of the newly established Dominion Astrophysical Observatory at Victoria, British Columbia, for which he had organized the design, construction, and installation of a new 72-inch (1.8-m) reflecting telescope. He retired in 1935.

Plaskett's field of research was spectroscopy, in particular the measurement of radial velocities of celestial bodies, i.e., their velocities along the line of sight, from the shift in their spectral lines. Using the 72-inch reflector and a highly sensitive spectrograph, many spectroscopic binary systems were discovered. In 1922 Plaskett identified an extremely massive star as a binary, now known as Plaskett's star. In 1927 Plaskett provided confirmatory evidence for the theory of galactic rotation put forward by Bertil Lindblad and Jan Oort.

By 1928 Plaskett, in collaboration with J.A. Pearce, had obtained evidence for the hypothesis formulated by Arthur Eddington in 1926 that interstellar matter was widely distributed throughout the Galaxy; their results showed that interstellar absorption lines, mainly of calcium, took part in the galactic rotation and so the interstellar matter was not confined to separate star clusters. Although this result was first announced by Otto Struve in 1929, Plaskett felt he had priority and was convinced that Struve had obtained his results from him.