Clyde Tombaugh

Clyde Tombaugh was an American astronomer who discovered the dwarf planet Pluto in 1930. Tombaugh, a self-taught amateur astronomer who had built his own telescopes and sent detailed sketches of Jupiter and Mars to Lowell Observatory, was hired there in 1929 and assigned the painstaking task of continuing astronomer Percival Lowell's earlier search for a hypothesized ninth planet, referred to as Planet X, believed to be causing small irregularities in the observed orbits of Uranus and Neptune. Working systematically through photographic plates of the night sky taken several nights apart, Tombaugh used an instrument called a blink comparator to rapidly compare pairs of images and spot any object that had shifted position against the fixed background of stars. On February 18, 1930, Tombaugh identified exactly such a moving object on plates he had taken the previous month, and Lowell Observatory publicly announced the discovery of the new planet, later named Pluto, on March 13, 1930. Tombaugh continued a long career as an astronomer after the discovery, later working on the Zeta program to search for signs of extraterrestrial intelligence and teaching astronomy for many years at New Mexico State University.