Percival Lowell suggests the existence of Pluto.

The Bostonian and amateur astronomer theorizes the existence of Pluto based on his observations of the perturbations in the orbit of Neptune. Pluto’s existence is eventually proven through photographic evidence captured by Clyde Tombaugh at the Lowell Observatory, which was built by Lowell, in Flagstaff, Arizona, on February 181930. Originally called “Planet X,” it is named Pluto on May 30, 1930. Whether by coincidence or not, the name begins with Lowell’s initials, which are also the astronomical symbol, PL. Pluto is redefined as a “dwarf planet” by a vote of the International Astronomical Union in Cambridge on August 24, in 2006.