Working at the Lowell Observatory in Flagstaff, Arizona, Tombaugh carefully looked for the so-called Planet X using a device called a blink comparator. He compared images of the night sky taken at different times to look for objects that moved between frames.
Pluto lost its status as a planet in 2006 when it was reclassified as a Kuiper Belt dwarf planet.
Photo: Clyde Tombaugh using his blink comparator (Science Photo Library)
An American astronomer discovers Pluto in 1930.
Now demoted to dwarf planet status, Pluto is still an important world.
Astronomer Clyde Tombaugh discovered Pluto in 1930 by meticulously comparing images of the night sky. Pluto held its planet status until 2006 when it was reclassified as a dwarf planet, one of many bodies orbiting in an area known as the Kuiper Belt. It is now known that Pluto does not mark the edge of the Solar System.
Clyde William Tombaugh (February 4, 1906 – January 17, 1997) was an American astronomer. Although he is best known for discovering the dwarf-planet Pluto in 1930, the first object to be discovered in what would later be identified as the Kuiper belt, Tombaugh also discovered many asteroids; he also called for the serious scientific research of unidentified flying objects, or "U.F.O.s".