James Christy noticed a bulge on Pluto, which turned out to be its satellite. The image on the left, greatly magnified, shows what Christy observed. The specks are emulsion grains from the film. On the right is the configuration of Pluto and Charon when the photograph was taken.
Twice in Pluto's 248-year orbit, Charon's orbit is seen edge on to the Earth. During this five-year period, Pluto and Charon eclipse each other, providing valuable data about the planet-satellite system. These eclipses began shortly after Charon was discovered. This diagram below shows the orientation of Charon's orbit relative to Earth between 1982 and 1994.
Adapted from Mark Littmann, Planets Beyond (John Wiley & Sons, 1990).