Clyde Tombaugh

Clyde William Tombaugh was an American astronomer who discovered Pluto in 1930 — the only planet (later reclassified as dwarf planet) discovered by an American. Born on a farm in Streator, Illinois, Tombaugh was largely self-taught in astronomy. Unable to afford college, he built his own telescopes and made detailed drawings of Jupiter and Mars, which he sent to the Lowell Observatory in Flagstaff, Arizona. Impressed by his work, the observatory hired the 23-year-old to conduct a systematic photographic search for a predicted "Planet X" beyond Neptune. Using a blink comparator to painstakingly compare photographic plates taken days apart, Tombaugh found a tiny moving object on February 18, 1930. The discovery made him world-famous overnight. He later earned his bachelor's and master's degrees at the University of Kansas. In 2006, nine years after his death, Pluto was controversially reclassified as a dwarf planet. In 2015, a small amount of his ashes traveled aboard NASA's New Horizons spacecraft during its historic flyby of Pluto.

Discovered Pluto on February 18, 1930, through systematic photographic plate comparison. Discovered hundreds of asteroids, variable stars, and star clusters during his photographic surveys. Demonstrated that amateur astronomers with determination can make world-changing discoveries. His ashes traveled aboard New Horizons during its Pluto flyby in 2015. Searched over 90 million star images in his systematic sky survey at Lowell Observatory.