Tombaugh, Clyde William

▪ 1998

      American astronomer (b. Feb. 4, 1906, Streator, Ill.—d. Jan. 17, 1997, Las Cruces, N.M.), discovered the planet Pluto, the ninth planet in the solar system and the only one found in the 20th century. Tombaugh was 24 years of age when he made the discovery in 1930 at Lowell Observatory in Flagstaff, Ariz. At that time he had had no formal training in astronomy, only a keen interest that had been sharpened by his first glimpse of the heavens through his uncle's telescope. After finishing high school, Tombaugh built his own telescope according to specifications published in a 1925 issue of Popular Astronomy. Using this instrument, he made observations of Jupiter and Mars and sent sketches of these planets to Lowell Observatory, hoping to receive advice about his work. Instead, he received a job offer. Tombaugh's assignment was to locate the ninth planet, a search instigated in 1905 by astronomer Percival Lowell. To carry out this task Tombaugh used a 33-cm (13-in) telescope to photograph the sky and an instrument called a blink comparator to examine the plates for signs of moving celestial bodies. On Feb. 18, 1930, Tombaugh pinpointed Pluto, and on March 13 Lowell Observatory announced the discovery of the new planet. After his discovery Tombaugh attended the University of Kansas on a scholarship, returning each summer to the observatory until completing (1939) his M.A. in astronomy. Upon graduating he returned to the observatory and continued his patrol of the skies, cataloging more than 30,000 celestial objects before he left in 1946. His observations of Mars led him to conclude in 1950 that the surface of the planet would be pitted with craters as a result of its proximity to the asteroid belt, a prediction borne out by images taken by the Mariner 4 space probe in the 1960s. Tombaugh also taught at Arizona State College and at the University of California, Los Angeles, and he worked as an astronomer and optical physicist at White Sands Missile Range near Las Cruces, N.M., where he helped set up an optical tracking system to follow ballistic missiles. He joined the faculty of New Mexico State University in 1955 and there instituted a major program of planetary research. He retired in 1973 but remained involved as an observer and adviser at the university. In 1980 he published, with Patrick Moore, Out of the Darkness: The Planet Pluto.

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