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The discovery of Charon
Artist's drawing of the New Horizons spacecraft in space


In 1978, the U.S. Naval Observatory was making measurements to refine Pluto's orbit. Astronomer James Christy noticed that a number of the Pluto images appeared elongated. These Pluto images show a normal, roughly circular image on the right, and an elongated one on the left. Upon further study, Christy concluded that the only explanation was a previously unknown moon, now called Charon, with an orbital period of just over six days.