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Forget that mnemonic for the names of the nine planets! There's… - CERisE's Testing for L

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August 17th, 2006

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02:59 pm
Forget that mnemonic for the names of the nine planets! There's three more!

For a long while, there's been questions about whether Pluto should be called a planet. The IAU is going to vote in a definition on Thursday of next week which defines a planet as a mass which undergoes hydrostatic equilibrium and does not orbit another planet (which is to say that the center of its orbit is not a point located on or under the surface of another planet).

Therefore, not only is Pluto a planet, but Charon (a "moon" of Pluto's (though it's really a planet in its own right and the two of them are double planets)), Ceres (The largest asteroid in the belt between here and Mars), and UB 313 (casually known as "Xena" until the IAU adopts a better name for it).

An amusing thought -- I'm sure we've all at least heard of people going out to a field and pacing off from points in order to give a scaled down idea of how far apart the planets are. UB 313 is approximately twice as far out as Pluto. The Boston Museum of Science has a static exhibit with scale models of the planets. At present, Pluto is approximately 10 miles away. Aphelion for UB313 is 97.56 AU compared to Pluto's 49.31...that'd put it another 10 miles out of Boston.

In other space-related bits and tids, Voyager I -- the farthest flung manmade object at the moment -- just passed 100 AU from the sun.

At the moment, I'm doing the unthinkable and *not* playing nethack. I had a *very* good game -- good enough for #2 on the rankings on b. I lost when my character was zapped by a wand of death from a soldier -- an otherwise trivial monster. I never had a chance. I never ran across any magic resisting or reflecting items. Just zap. Dead. No chance to avoid it. =(

(2 comments | Leave a comment)


[User Picture]
Date:August 18th, 2006 03:19 am (UTC)
wait, there's a *mnemonic* for remembering the planets? I've never been taught that...These are the things I missed by having the first 8 years of my education taught completely in French - there's obviously no mnemonic in French for the names of the planets...

I heard on the radio today that the IAU have revised the definition of a planet to be a) must have enough of a gravitational field to keep itself in a relatively round shape and b) must orbit a star, and not some other body.

Makes me wonder, what exactly was the *old* definition?

[User Picture]
Date:August 18th, 2006 09:47 am (UTC)
There's a ton of them. I'm not surprised you didn't learn it with French as a first language though. The French have probably been too busy arguing about what the French word for "planet" should be and how it should be different from other Romance languages to be very interested in what they are. ; )

That definition isn't decided yet. It's been drafted and it's likely to be accepted. The actual vote is on the 24th in Prague.

The old definition was something like "a lump of mass in orbit around a star". There was a distinction between major and minor planets (for example, Ceres -- an asteroid which would be considered a planet by the new definition -- was actually considered a "minor planet"), but it was subjectively drawn. That led to arguments about whether or not Pluto was a planet.

The new one's a much better definition, although it's likely that more than 12 planets will be forthcoming.

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