Clyde William Tombaugh


Clyde W. Tombaugh in Flagstaff, Arizona, 1931

American astronomer Clyde William Tombaugh was born in Streator, Illinois, on February 4, 1906. He was raised on farms in Kansas and became interested in astronomy as a boy. In 1926, at the age of 20, Tombaugh built his first telescope. Using his homemade telescopes, he made drawings of the planets Mars and Jupiter and sent them to Lowell Observatory in Flagstaff, Arizona. The astronomers at Lowell were so impressed with the young amateur’s powers of observation, they invited him to work at the observatory. Tombaugh worked there from 1929 to 1945.

   Vesto Melvin Slipher (1875–1969), director of the observatory, commissioned Tombaugh to resume the search for Planet X, which had previously been led by Percival Lowell (1855–1916), founder of the Lowell Observatory. Tombaugh's task was to systematically image the night sky in pairs of photographs, then examine each pair and determine whether any objects had shifted position using a blink comparator. Tombaugh’s search had been underway for 10 months before he found Pluto on plates exposed on January 23 and 29 and blinked on February 18, 1930. The discovery was announced on March 13, 1930. At the time of discovery, Pluto was considered the planet, but was reclassified as a dwarf planet in 2006.

   In 1932, Tombaugh entered the University of Kansas, where he earned his bachelor of science degree in 1936. He continued to work at Lowell Observatory and in 1938 received a master’s degree from the University of Kansas. Tombaugh also discovered 15 asteroids, a comet, and hundreds of variable stars, star clusters and galaxy clusters. He worked on the captured V-2 rockets at White Sands, and became professor at New Mexico State University, where he confirmed the rotation period of Mercury on its axis, determined the vortex nature of Jupiter’s Great Red Spot, and looked for small, natural Earth satellites. He died on January 17, 1997.

Discovery images of Pluto. Credit: Lowell Observatory

Clyde Tombaugh circa 1930 at his family's farm with his homemade telescope


© 2026, Andrew Mirecki

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