Pluto Discovered: Tombaugh Expands the Solar System

Clyde Tombaugh was a 24-year-old Kansas farm boy without a college degree when he discovered Pluto on February 18, 1930, by comparing photographic plates taken weeks apart through the 13-inch telescope at Lowell Observatory in Flagstaff, Arizona. Percival Lowell had predicted the existence of a 'Planet X' beyond Neptune based on gravitational calculations that later proved erroneous. Tombaugh found Pluto anyway, through sheer diligence: he spent months systematically photographing the sky and comparing plates by hand using a blink comparator. The discovery made global headlines and prompted an 11-year-old English girl named Venetia Burney to suggest the name Pluto, after the Roman god of the underworld. Pluto was classified as the ninth planet for 76 years until the International Astronomical Union reclassified it as a 'dwarf planet' in 2006, a demotion that remains controversial among both the public and some astronomers. Tombaugh died in 1997; his ashes flew aboard the New Horizons probe that passed Pluto in 2015.