Posted
on June 22, 2015
What
was up with Pluto?
That's
what U.S. Naval Observatory astronomer James Christy was wondering as
he studied Pluto through a telescope. It looked...bulgy!
 |
| Left, Pluto bulgy. Right, Pluto round and non-bulgy. |
As
Christy continued to make observations, he realized that the
bulginess was different at different times. It didn't make sense that
Pluto itself would be have a bulge that moved around its middle and
sometimes disappeared. It made more sense that Pluto had a companion
whose reflected sunlight seemed to merge with the sunlight reflecting
from Pluto.
Christy
made this discovery on this date in 1978. The discovery was announced
to the world in early July.
Actually,
others had a chance to make the discovery. Christy wanted to check
his observation, and he was able to discover the periodic
Pluto-bulges in photos taken of the planetoid as far back as 1965.
For more than a decade, nobody had noticed the teeny elongation.
Pluto
is tiny, but Charon is large.
You've
probably heard that Pluto is so teeny that it lost its former label
of planet and is now considered a dwarf planet, planetoid, or
Plutoid. As a matter of fact, Pluto is the second largest of the
Plutoids in our solar system (only Ceres is larger).
But
Charon is a bit more than half the size of Pluto. (Compare this to
Earth's moon, which is only a tiny fraction of the size of the
Earth.) Charon isn't all that large compared to other solar system
moons (even Pluto is smaller than Earth's Moon, let alone Charon!) -
but the two are much closer in size than are other planet-satellite
comparisons.
What's
in a name?
Ancient
peoples had various names for the five planets that they could see
with their naked eyes, but European scientists ended up using the
names used by Ancient Roman astronomers. Those names were the names
of their gods and goddesses: Venus, Mars, Mercury, Jupiter, and
Saturn. When more planets were discovered in the modern era,
scientists decided to maintain the custom of naming the planets after
Roman deities. That's how we ended up with Uranus, Neptune, and
Pluto.
Pluto
is the Roman name for the Roman god of the underworld, the god who
the Greeks called Hades.
One
of the beings associated with Pluto-the-Roman-god is Charon. Charon
is the ferryman who transported the dead to the underworld.
Coincidentally, the guy who discovered Pluto's moon—and therefore
got to name it—had a wife named Charlene. He called her “Char.”
Christy loved the nod to his wife while sticking to Roman
mythological sources for the name of his discovery.
But
the Greeks pronounced “Ch” as a hard “K” – and so the name
of the Roman ferryman was pronounced Karon. And Christy's wife's name
had “Ch” pronounced like “Sh” – “Shar” for “Sharlene.”
This explains why many speakers of other languages, and also many
English-speaking astronomers, call Pluto's moon “Karon,” but some
English-speaking astronomers, the discoverer himself, and NASA all
pronounce the name “Sharon.”
Actually, the two different ways of pronouncing the name has led to the “Sh” version being a shibboleth of sorts. A shibboleth is a version or pronunciation of a word that is used by an in-group, the people “in the know.”
Actually, the two different ways of pronouncing the name has led to the “Sh” version being a shibboleth of sorts. A shibboleth is a version or pronunciation of a word that is used by an in-group, the people “in the know.”
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