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  •  That's what I meant (0+ / 0-)

    Pluto and Charon orbit a common barycentre = they orbit around each other. I read that on the wiki entry but put it into everyday language. Oh Look! "Charon and Pluto revolve about each other".

    "the barycentre of the Earth-Moon system, like that of the Pluto-Charon system, does not coincide with the center of Earth's gravity"

    But it's still inside of the Earth, unlike that of Pluto/Charon.

    "Does that make the Sun not a star?  Or make the Sun-Jupiter system a "double star"?"

    Why on Earth would you think that? I think you're being silly.

    I can, of course, talk about "the planet Pluto".  Why shouldn't I be able to?

    I just think it's odd you know. When I was little there was only this one single entity, Pluto. Now that's gone and been replaced by two bodies orbiting each other. From the link above:

    The center of mass (barycenter) of the Pluto-Charon system lies outside either body. Since neither object truly rotates around the other, and Charon has 11.6% the mass of Pluto, it has been argued that Charon should not be considered to be a satellite of Pluto. Instead, it has been suggested that they form dual dwarf planets, following the re-classification of Pluto.

    In a draft proposal for the 2006 redefinition of the term, the International Astronomical Union proposed that a planet be defined as a body that orbits the sun that is large enough for gravitational forces to render the object (nearly) spherical. Under this proposal, Charon would have been classified as a planet, since the draft explicitly defined a planetary satellite as one in which the barycenter lies within the major body. In the final definition, Pluto was reclassified as a dwarf planet, but the formal definition of a planetary satellite was not decided upon, leaving Charon's status unclear. (Charon is not in the list of dwarf planets currently recognized by the IAU.)

    So Pluto and Charon are like two ends of a barbell spinning in space. The central point they spin around is not within the surface of either. Even though Charon is one tenth the size of Pluto why not consider both to be planets or dwarf planets?

    If the Earth had a "moon" the relative size of Charon, 11%, and they both orbited each other like Pluto/Charon do, wouldn't that hypothetical Earth's moon be pretty damn big and really.... we would think of it as a planet wouldn't we?

    There is a great deal of pain in life and perhaps the only pain that can be avoided is the pain that comes from trying to avoid pain. - R.D. Laing

    by brenda on Sun Mar 01, 2009 at 05:36:21 PM PST

    [ Parent ]

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