Science Fair Project Encyclopedia
James W. Christy
James Walter Christy (born 1938) is an American astronomer.
Working at the United States Naval Observatory, he discovered in 1978 that Pluto had a moon, which he named Charon.
The discovery was made by carefully examining an enlargement of a photographic plate of Pluto and noticing it had a very slight bulge on one side. By examining images taken over several successive days, he was able to convince himself that it was a moon. The photographic evidence was considered convincing but not conclusive; however, based on the orbit determined, a series of mutual eclipses of Pluto and Charon was predicted and observed, which provided confirmation.
In more modern telescopes, such as the Hubble Space Telescope or ground-based telescopes using adaptive optics, separate images of Pluto and Charon can very easily be resolved.
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