Today in 1930, the planet Pluto was discovered by Clyde Tombaugh, the only planet to be found by an American astronomer, after three decades of work at Lowell Observatory in Flagstaff, Arizona. Before Tombaugh was born, Percival Lowell had searched unsuccessfully for Pluto, a ninth planet whose gravity would explain deviations in the positions of Uranus and Neptune. In his will he decreed that the hunt should continue. That meant using a telescope to photograph tiny pieces of the sky by night, then and sifting through the millions of star images by day for one dim dot that moved. When Lowell Observatory director Vesto Slipher hired him, a Kansas farm boy, Clyde Tombaugh threw himself into the search in Apr 1929. Pluto is now considered a dwarf planet, the second-largest in the Solar System (after Eris), and the tenth-largest body observed directly orbiting the Sun. Pluto is now considered the largest member of a distinct population called the Kuiper belt.