"wnowak" wrote in message
...
took place on 18th of February 1930 - almost exactly 75 years ago.

However, the sattelite of PLuto Charon remained not discovered for ...
48 YEARS !
It was ACCIDENTLY discovered on pictures of PLuto in 1978.

The technology needed to discover Charon existed for all 48 years ( from
1930 to 1978 ).

Why it was not discovered ?

http://www.interlog.com/~wnowak/book




It's sometimes hard to explain why something was not noticed for a long
time, but the usual answer is, no one looked hard enough, or possibly Charon
was occasionally seen, and dismissed as a flaw or background star.

Pluto was not regarded as a subject of great interest by most astronomers in
the '40s and '50s, except for the question of its size and mass. The best
way to look for evidence of mass was to measure deviations in the orbits of
Uranus and Neptune, so observational approaches were directed at accurate
observations of these other planets.

Back in the 1960s an effort to observe an occultation of a star by Pluto
produced upper limits for its size, and showed that Pluto was much smaller
than Earth, but Charon did not happen to occult the star for any observer.

You also have to remember that most photographic observations of Pluto were
done to determine or improve its orbit, so only relatively small telescopes
were used, such as astrographs, or long focus refractors adequate for the
task but often located in places with relatively poor seeing. Charon is
always within a second of arc or so of Pluto itself and would be extremely
hard to spot on such photographs.

It was only when Christy used a relatively large (1.5-m, ISTR) telescope to
get precise astrometry from a high-quality mountaintop site (for prediction
of possible occultations) that he noticed a small bump on one side of the
planet's image. He might have simply dismissed it as a background star or a
flaw, but because it was on several images in different positions he
realised it was a satellite.

This said, I recall that Gerard Kuiper observed Pluto visually with the
Palomar 5-m telescope in the late 40s or early 50s, on a night of excellent
seeing. He wanted to measure the diameter with a bifilar micrometer (or
similar), and it is slightly surprising that he did not spot Charon. Or
maybe he did, and dismissed it as a faint background star. Remember, this
was a single observation on one night.

--
Mike Dworetsky

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