PLASKETT, JOHN STANLEY

PLASKET, JOHN STANLEY (b. Hickson, near Woodstock, Ontario, 17 November 1865; d. Esquimalt, near Victoria, British Columbia, 17 October 1941)

astronomy.

Plaskett’s chief contributions to astronomy were in instrumental design and the supervision of a lengthy program of observation, especially of spectroscopic binary stars.

Plaskett was the son of Joseph and Annie Plaskett. He was educated at the local village school and the Woodstock High School. He left school to work on the family farm but soon was employed by a mechanic in Woodstock. He then went to the Edison Electric Company, first in Schenectady, New York, and later in Sherbrooke, Quebec. In 1889 Plaskett was a mechanic in the department of physics at the University of Toronto. He took the opportunity first to matriculate and then to take up undergraduate studies, which he followed concurrently with his other work. In 1892 he married Rebecca Hope Hemley, and with her encouragement he eventually graduated in physics and mathematics in 1899. He remained a mechanic until 1903, but in his final years at Toronto he was engaged in research in color photography.

From 1903 Plaskett was on the staff of the new Dominion Observatory in Ottawa. He worked with the spectrograph and measured radial velocities with the fifteen-inch reflector; and after making a careful study of the mechanical problems involved and discussing the matter with the staffs of many American observatories, he designed a new spectrograph for the reflector. It is claimed that his design so increased the speed of this instrument that for radial velocity work it became the equal of the Yerkes refractor.

After persistently recommending that the Canadian Parliament build a seventy-two-inch reflector, Plaskett prevailed and the contracts were signed in 1913. Much of the design was Plaskett’s own. In 1917 he was appointed director of the Dominion Astrophysical Observatory in Victoria, British Columbia, which opened in 1918. Again he and his staff concentrated on the observation of radial velocities. New binaries were discovered and their orbits measured, these binaries including “Plaskett’s twins.” This star system, which Plaskett was the first to realize was not a single star (B.D. + 6° 1309), was long the most massive known (1922). He gave particular attention to early type O and B stars, and he studied the motion and distribution of interstellar calcium. But perhaps his most notable achievement was his application of spectroscopic evidence to the problem of galactic rotation and the distance and direction of the center of gravity of the galaxy, those being determined from the motions of stars of spectral types O5 to B7 (1930).

Plaskett retired in 1935. He was elected a fellow of the Royal Society, was president of the Royal Astronomical Society of Canada, and received medals from six societies in North America and Great Britain. After his retirement he supervised the grinding and polishing of the eighty-two-inch mirror for the McDonald Observatory at the University of Texas. One of his two sons, Harry Hemley Plaskett, became Savilian professor of astronomy at Oxford.

BIBLIOGRAPHY

I. Original Works. C. S. Beals et al., “Bibliography of the Published Papers of J. S. Plaskett,” in Journal of the Royal Astronomical Society of Canada, 35 (1941), 408–411, lists 85 works. Those cited in the text are “A Very Massive Star,” in Monthly Notices of the Royal Astronomical Society, 82 (1922), 447–500; “The Radial Velocities of 523 O- and B-Type Stars Obtained at Victoria,” in Publications of the Dominion Astrophysical Observatory, Victoria, B.C., 5 (1931), 1–98, written with J. A. Pearce; and “A Catalogue of the Radial Velocities of O- and B-Type Stars,” ibid., 99–165, written with J. A. Pearce. Plaskett’s most substantial memoirs appeared in vols. 1–5 (1920–1934) of this journal.

II. Secondary Literature. See A. C. D. Crommelin, “Address … on the Award of the Gold Medal of the Society …,” in Monthly Notices of the Royal Astronomical Society, 90 (1930), 466–477. Obituaries are F. S. Hogg, ibid., 102 (1942), 70–73; R. O. Redman, in Observatory, 64 (1942), 207–211; and R. F. Sanford, in Astrophysical Journal, 98 (1943), 137–141, with portrait. See also the article by R. O. Redman in Dictionary of National Biography, supp. 6 (1941–1950), 675–676.

J. D. North