Planet X— X Planet
In 1894, American astronomer Percival Lowell moved to Flagstaff, Arizona to set up an observatory – the high elevation of the small city offered clear air and the climate promised nearly year-round visibility. He had two goals – finding proof of intelligent life on Mars, and finding Planet X. Although he used models to predict Planet X’s location and search the right part of the sky, he never found it before his death in 1916. (Lowell at work at the observatory that still bears his name.) The hunt resumed at the Lowell Observatory in 1929 when Illinois-born astronomer Clyde Tombaugh arrived. He used a blink comparator, a machine that alternated between two images of the night sky, to detect a moving object. Stars won’t move from night to night, but planets will. On February 18, 1930, Tombaugh found a tiny moving dot in two of his images. By May 1, his discovery of Planet X was accepted around the world and had been formally named Pluto.