The largest moon of Pluto discovered

June 22, 1978: The largest of Pluto's five moons, Charon, was discovered in June 1978 by James Christy and Robert Harrington at the U.S. Naval Observatory in Flagstaff, Arizona – about six miles from where Pluto was discovered at the Lowell Observatory. They weren't even looking for moons. They were trying to refine Pluto's orbit around the Sun. Charon was discovered in 1978 when astronomer James Christy noticed images of Pluto were strangely elongated. The blob seemed to move around Pluto. The direction of elongation cycled back and forth over 6.39 days – Pluto's rotation period. Searching through their archives of Pluto images taken years before, Christy found more cases where Pluto appeared elongated. Additional images confirmed he had discovered the first known moon of Pluto.