William Pickering was an American astronomer who believed there was a planet outside the orbit of Neptune that caused the unusual shape of the orbit of Neptune and Uranus. He was instrumental in the establishment of Lowell observatory in Flagstaff, Arizona with Percival Lowell to search for this "Planet X". Powell spent the rest of his life searching, even photographing Pluto on film twice without recognizing the planet.
Clyde Tombaugh joined the staff at Lowell Observatory and was given the task of taking systematic photographs of portions of the night sky on two nights one week apart. He would load the images in a device called a blink comparator that rapidly switches the two photographs. This allowed Tombaugh to detect slight differences between the photographs which would suggest movement. He found a change from his late January plates and confirmed the discovery with another photograph. He had discovered a new planet and the formal announcement was made on March 13, 1930.
The name "Pluto" was chosen from a selection of submitted possible names. It originally came from an 11-year-old girl from Oxford, England named Venetia Burney. Find out what else occurred on this day in science history.