more on We now have 12 planets... give or take...

[David Farber <dave () farber net>]

Begin forwarded message:

From: "William S. Duncanson" <caesar () starkreality com>
Date: August 24, 2006 3:29:15 PM EDT
To: dave () farber net
Subject: RE: [IP] We now have 12 planets... give or take...

Dr. Farber,

For IP, if you wish,

This is somewhat contrary to the various other news reports that have  
been
going around, and contrary to the news article cited.  There are now 8
planets, and a new class of object called "dwarf planets" that aren't  
really
considered planets, which is somewhat confusing given the name.  From  
the
IAU resolution, a "planet" is a body that orbits the sun, is in  
hydrostatic
equilibrium (spherical or almost so) and has cleared the neighborhood  
around
it's orbit.  A "dwarf planet" is a body that orbits the sun, is in
hydrostatic equilibrium, has not cleared the neighborhood around it's  
orbit,
and is not a satellite.

So, now there are 8 planets, and a dozen or so "dwarf planets", of which
Pluto is considered to be the prototypical example.

This definition is still somewhat controversial, given the presence of
near-earth objects and the Trojan asteroids in Jupiter's orbit, so  
while an
official definition finally exists of the term "planet", it might change
again in the foreseeable future.

--
William S. Duncanson
caesar () starkreality com

-----Original Message-----
From: David Farber [mailto:dave () farber net]
Sent: Thursday, August 24, 2006 13:49
To: ip () v2 listbox com
Subject: [IP] We now have 12 planets... give or take...



Begin forwarded message:

From: Joseph Lorenzo Hall <joehall () gmail com>
Date: August 24, 2006 11:54:00 AM EDT
To: Dave Farber <dave () farber net>
Subject: We now have 12 planets... give or take...
Reply-To: joehall () pobox com

The International Astronomical Union has voted (and passed) a new  
definition
scheme as to what constitutes a "planet".

The Final IAU Resolution on the definition of "planet" ready for voting.
<http://www.spaceref.com/news/viewpr.html?pid=20674>

A "planet" is an object orbiting the Sun that is large enough to form a
rough sphere (when gravity balances pressure).  Any object orbiting a  
planet
is a satellite (unless the center of mass of their orbit is outside the
primary object, like Pluto and Charon, which are now both dwarf  
planets).

(There's some speculation that the definition involved would make  
Earth and
Jupiter not actual planets because they haven't "cleared the  
neighbourhood
around its orbit" (Near-Earth Objects and Trojan Asteroids  
respectively).)

What are the other three "planets" that have been added to the  
traditional
nine?  Well, Pluto's "moon" [Charon][1] is now a planet.
The asteroid [Ceres][2], which is large enough to be spherical and  
orbits
the Sun is now a planet.  Finally, a recently discovered large and round
object that is larger than Pluto, [UB313][3], is also a planet. -Joe

[1]: http://en.wikipedia.org/wiki/Charon_%28moon%29
[2]: http://en.wikipedia.org/wiki/1_Ceres
[3]: http://en.wikipedia.org/wiki/2003_UB313


--
Joseph Lorenzo Hall
PhD Student, UC Berkeley, School of Information <http://josephhall.org/>


--
Joseph Lorenzo Hall
PhD Student, UC Berkeley, School of Information
<http://josephhall.org/>


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