In 1978, evidence of the first moon of Pluto was discovered by astronomer James W. Christy of the Naval Observatory in Flagstaff, Ariz. when he obtained a photograph of Pluto that showed the orb to be distinctly elongated.. Furthermore, the elongations appeared to change position with respect to the stars over time. After eliminating the possibility that the elongations were produced by plate defects and background stars, the only plausible explanation was that they were caused by a previously unknown moon orbiting Pluto at a distance of about 19,600 kilometers (12,100 miles) with a period of 6.4 days. The moon was named Charon, after the boatman in Greek mythology who took the souls of the dead across the River Styx to Pluto's underworld. Pluto and Charon, by Isaac Asimov and Richard Hantula. - book suggestion.