An American astronomer who discovered Pluto in 1930. Tombaugh began his search for the trans-Neptunian planet, which Percival Lowell had predicted, in 1929 when he became an assistant at Lowell Observatory. Using a blink comparator, he compared pairs of photographs taken a week apart. He was rewarded on February 18, 1930, when he spotted an object that showed movement between two plates exposed the previous month. Tombaugh later searched, without success, for a tenth planet and for small moonlets of Earth, though he did find in the process new star clusters and galaxy clusters and almost 800 asteroids.
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