June 22 – A Moon for Pluto!

nPostednon June 22, 2015

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nWhatnwas up with Pluto?

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nThat’snwhat U.S. Naval Observatory astronomer James Christy was wondering asnhe studied Pluto through a telescope. It looked…bulgy!

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Left, Pluto bulgy.
Right, Pluto round
and non-bulgy.

nAsnChristy continued to make observations, he realized that thenbulginess was different at different times. It didn’t make sense thatnPluto itself would be have a bulge that moved around its middle andnsometimes disappeared. It made more sense that Pluto had a companionnwhose reflected sunlight seemed to merge with the sunlight reflectingnfrom Pluto.

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nChristynmade this discovery on this date in 1978. The discovery was announcednto the world in early July.

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nActually,nothers had a chance to make the discovery. Christy wanted to checknhis observation, and he was able to discover the periodicnPluto-bulges in photos taken of the planetoid as far back as 1965.nFor more than a decade, nobody had noticed the teeny elongation.

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nPlutonis tiny, but Charon is large.

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You’venprobably heard that Pluto is so teeny that it lost its former labelnof planet and is now considered a dwarf planet, planetoid, ornPlutoid. As a matter of fact, Pluto is the second largest of thenPlutoids in our solar system (only Ceres is larger).

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nButnCharon is a bit more than half the size of Pluto. (Compare this tonEarth’s moon, which is only a tiny fraction of the size of thenEarth.) Charon isn’t all that large compared to other solar systemnmoons (even Pluto is smaller than Earth’s Moon, let alone Charon!) -nbut the two are much closer in size than are other planet-satellitencomparisons.

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nWhat’snin a name?

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nAncientnpeoples had various names for the five planets that they could seenwith their naked eyes, but European scientists ended up using thennames used by Ancient Roman astronomers. Those names were the namesnof their gods and goddesses: Venus, Mars, Mercury, Jupiter, andnSaturn. When more planets were discovered in the modern era,nscientists decided to maintain the custom of naming the planets afternRoman deities. That’s how we ended up with Uranus, Neptune, andnPluto.

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nPlutonis the Roman name for the Roman god of the underworld, the god whonthe Greeks called Hades. n

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nOnenof the beings associated with Pluto-the-Roman-god is Charon. Charonnis the ferryman who transported the dead to the underworld.nCoincidentally, the guy who discovered Pluto’s moon—and thereforengot to name it—had a wife named Charlene. He called her “Char.”nChristy loved the nod to his wife while sticking to Romannmythological sources for the name of his discovery.

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nButnthe Greeks pronounced “Ch” as a hard “K” – and so the namenof the Roman ferryman was pronounced Karon. And Christy’s wife’s namenhad “Ch” pronounced like “Sh” – “Shar” for “Sharlene.”nThis explains why many speakers of other languages, and also manynEnglish-speaking astronomers, call Pluto’s moon “Karon,” but somenEnglish-speaking astronomers, the discoverer himself, and NASA allnpronounce the name “Sharon.”

Actually, the two differentnways of pronouncing the name has led to the “Sh” version being anshibboleth of sorts. A shibboleth is a version or pronunciation of anword that is used by an in-group, the people “in the know.” n

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nAlsonon this date: