Tombaugh, Clyde William

[ tom bow] (1906–97) US astronomer: discovered Pluto.

Too poor to attend college, Tombaugh was a keen amateur astronomer and built his own 9 in (23 cm) telescope. He was appointed as an assistant at the Lowell Observatory, Arizona, in 1929, and took over search for a trans-Neptunian planet; Lowell had died in 1916. After repeatedly photographing the sky along the plane of the ecliptic, and checking for differences between successive photographs with a blink comparator, Tombaugh finally announced the finding of the new planet (Pluto) on 13 March 1930. Afterwards he continued the search for possible further planets, but although he discovered over 3000 asteroids, he found no other planets.

Pluto, the outermost of the planets, is in several ways unusual: its orbit is highly eccentric and is tilted, it is much smaller than the other outer planets and it has a relatively large satellite, Charon, with which it is locked in synchronous rotation, each keeping the same side facing the other. Pluto is named after the Greek god of the underworld, and the name also honours (through his initials) , who predicted its existence.