Re: Pluto (was: Re: Naming days of the week and months of the year????)

> From: Robert Hailman
>
> Henrik Theiling wrote:
> >
> > Hi!
> >
> > Nik Taylor <fortytwo@...> writes:
> > > Raymond Brown wrote:
> > > > We now have nine planets - but a nine-day week is too long
> > >
> > > Some astronomers don't consider Pluto a planet (in fact,
> didn't the IAU
> > > officially declare it not a planet?
> >
> > Hmm??  Who not?  It circles around the sun, ergo it's a planet.
> >
> > *Puzzled*...
>
> I don't know if it was recently declared not a planet, but I do know
> that there are people who don't consider it one.
>
> The main reason is that it's much too small to be a planet, really. It's
> more of a lone asteroid, or moon.
>
> Maybe some one else can shed more light on this.
Aha, mixing my two hobbies (conlanging and astronomy) on one list!

In fact, Pluto is a planet, although circling the sun is not sufficient
reason for proclaiming it so. Lots of stuff circles the sun.  The
organization that decides the classification of objects in the solar system,
the International Astronomical Union (IAU) was petitioned to change the
status of Pluto to that of a minor planet or asteroid, but it rejected this
petition and has no plans to change Pluto's status any time in the
foreseeable future (see: http://www.iau.org/IAU/FAQ/PlutoPR.html.)

The principle argument of the petition was Pluto's exceedingly small size.
Pluto is by far the smallest of the nine planets, being smaller even than
seven of the solar system's moons.  Adding fuel to this debate was the
discovery of a number of large icy bodies in orbits beyond Pluto, in an area
known as the Kuiper Belt. These bodies are believed to be hundreds of
kilometers in diameter, leading to speculation that still larger bodies
(essentially giant comets) exist in this region, including some approaching
the size of Pluto. Recent studies of Pluto's composition have also led to
the idea that Pluto was once one of these bodies.

There is no set scientific law as to what constitutes a planet, but as a
rule of thumb, there are three properties of a planet:

1) It must (directly) orbit a star

2) It must be small enough that it has not been undergoing internal nuclear
fusion (i.e. it is not a star or star-like object)

3) It must be large enough that its self-gravity gives it the general shape
of a sphere.

However, under these rules, the asteroid Ceres could qualify as a planet. In
the final analysis, the designation of "planet" is more a historical issue
than a scientific one.

David

David E. Bell
The Gray Wizard
www.graywizard.net

Wisdom begins in wonder.