 Clyde Tombaugh was using a good-sized telescope when he discovered Pluto in 1930. He'd been searching for a possible planet beyond Neptune for about a year from Lowell Observatory in Arizona. When he found it, the little world was moving through Gemini. Almost a century later, Pluto has advanced only a third of the way around the sky. That's because Pluto is so remote that it takes 248 years to orbit the Sun.