Slag: If someone had told Plato that the earth was a planet & the sun was a star, he probably would have said "Yeah, and I'm Pluto". Likewise, muons were called mesons at first, but got demoted to leptons when pions etc. had been discovered and the situation became clearer. And when I was in school, there were only two kingdoms of life, and we learned (I forget on what grounds) that amoebae (amebe?) & sponges were animals and bacteria were plants. If you look up the definition of carbohydrate in some dictionaries, you will deduce that formaldehyde is a carbohydrate, but that's probably because whoever wrote the difinition didn't think of that.

Whatever formal definition people come up with, its treatment of Pluto is bound to be arbitrary-looking, because Pluto is an exceedingly anomalous object, really in a class by itself. Its orbit in particular is weird. It spends a good deal of its time closer to the sun than Neptune is. That made me wonder how close to Neptune it could get. Nowhere near, it turns out. Its orbital period is locked in a precise 3:2 resonance with Neptune's, so that whenever it gets close to Neptune's orbit, Neptune itself is on the far side of the sun. Pluto actually gets closer to Uranus than it ever gets to Neptune. That somewhat relieved me, because it had occurred to me that if it every got very close to Neptune, it might get whipped around into some horrible orbit that would make a mess of the inner planets. That opportunity, it seems, has been left to the human species.

--- Joe Fineman    joe_f@verizon.net

||: Sovereignty is the polite old-fashioned name for totalitarianism. :||