Tombaugh, Clyde William (1906-1997) was an American astronomer who discovered the dwarf planet Pluto. In the mid-1940's, he participated in ballistics research at White Sands Missile Range in New Mexico.
Tombaugh was born on a farm near Streator, Illinois, in 1906. In 1925, at age 18, Tombaugh constructed his first telescope, using a fence post as a grinding stand to grind the light collecting mirror. Although the telescope lacked the accuracy for the type of planetary observation he wanted, the experience started him on his lifetime career in astronomy.
In 1928, Tombaugh submitted drawings he had done of the planets to Lowell Observatory in Flagstaff, Arizona. The director was so impressed that he offered Tombaugh a job taking long-exposure photographs with the observatory's new telescope. Tombaugh began working for the observatory in January 1929.
Percival Lowell, for whom the observatory was named, had speculated 15 years earlier that a ninth planet existed beyond Neptune. Tombaugh photographed the night sky for several months, using a blink microscope to evaluate the pictures. A blink microscope rapidly alternates two photographic images, taken at different times, of the same area of the sky, which makes it easier to identify movement of a celestial body. An astronomer can then determine whether the moving object is a planet, asteroid, or comet. In February 1930, Tombaugh discovered a dot that had moved more than a star would, but less than an asteroid or comet. The astronomers at the observatory confirmed that he had found the ninth planet, which was named Pluto, and the discovery was announced on March 13, 1930.
Tombaugh's achievement earned him a full college scholarship. He earned a bachelor's degree (1936) and a master's degree (1939) from the University of Kansas. He remained at Lowell until 1946, then went to White Sands Missile Range, New Mexico, where he helped develop special optical guidance systems for tracking rockets in flight. From 1955 to 1973, he was professor of astronomy at New Mexico State University in Las Cruces.