(t m´bô) (KEY) , 1906–97, American astronomer, b. Streator, Ill. Although lacking formal training or a college degree, he was hired in 1929 as an assistant by the Lowell Observatory to continue the search for a planet beyond Neptune, which had been initiated by Percival Lowell. Tombaugh used a blink microscope to compare photographs of a small part of the night sky and detect the planet. After ten months of painstaking comparisons, on Feb. 18, 1930, he found Pluto in the constellation Gemini. After several weeks of observation by the observatory staff to validate the discovery, it was announced on Mar. 13, the 75th anniversary of Lowell’s birth. Tombaugh received a scholarship from the Univ. of Kansas, where he obtained his bachelor’s (1936) and master’s (1939) degrees. He subsequently returned to the observatory and also held several academic posts. He focused on planetary observations, particularly of Mars, and in 1965 images returned by the space probe Mariner 4 confirmed his prediction that the Martian surface would have craters caused by asteroid impacts. He wrote Out of the Darkness: The Planet Pluto (1980) with Patrick Moore.
See biography by D. H. Levy (1992).
