Clyde Tombaugh (1906-1997), US astronomer, who discovered Pluto in 1930. Tombaugh couldn't afford to study at college, but built his own telescope, and became an assistant at Lowell Observatory. Lowell himself predicted the existence of a ninth planet, and a team was set up to find it. Tombaugh invented the blink comparator to facilitate the search. This device allowed comparison of two photographs of the sky, which showed if any object had altered position. After 7000 hours of work, he found a tiny object outside the orbit of Neptune, which was named Pluto. In the course of his searches, he also discovered some 3000 asteroids.