Monday, August 21, 2006

Ceres And Her Companions
A reader suggested checking out APOD, the Astronomical Picture of the Day. That white patch in the upper right is probably an impact from another asteroid. Astronomy buffs might remember the interior bright material of Saturn's moon Phoebe from Cassini's 2004 encounter. Another definition hassle for the IAU will be the asteroid/comet boondoggle. Traditionally, asteroids were thought to consist of rock, metal, or both. Comets have been defined as celestial bodies made up of ice. (That's ice in the broad term of frozen material that would be liquid (water) or gas (methane, ammonia, etc.) at Earth temperatures. Yet there is not such a clear-cut boundary, and as we learn more about the composition of the asteroid belt, it seems many of those bodies might have a substantial ratio of ice. The distant body Chiron, orbiting between Saturn and Uranus, was thought to be an asteroid, but shortly after its discovery, it displayed some qualities of a comet, giving off gases and displaying a coma. (From the Latin for "hair," it refers to a temporary atmosphere when a comet approaches closer to the sun.) For the moment, Chiron is designated as both coment and asteroid. The Romans had it easier. They just lumped planets, stars, comets, and everything, under one word, sidus. The common translation of this hymn wouldn't pass ICEL's accuracy muster, as "stars of night" wouldn't be inclusive of all the wonderful hodgepodge of extra-terrestrial stuff.

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