tlhIngan-Hol Archive: Thu Feb 15 09:44:06 1996

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Re: KLBC:fractions & directions

>From the keyboard of Mark E. Shoulson
> Well, of *course* some rotate counter-clockwise... They *all* do---around
> their north poles.  You mean there's one which rotates counter-clockwise
> around its south pole?  I thought that was how you *defined* north and
> south in general.  Then in what sense is that pole its south pole?
> Magnetic?  Nobody ever said that a planet had to have a magnetic field, or
> that it had to be even vaguely aligned with its axis of rotation (or even
> pass through its center).  See Uranus for an imperfect counterexample.
> Alignment with the Sun's north pole?  Or its orbital path?  Those don't
> have to align in any way either (see Uranus some more).
> 
> So what *is* the definition, then?  Obviously I have it wrong; how is it
> defined?

This borders on issues unrelated to the Klingon language, so I'll try and be
brief.  There are two different poles associated with each planet (or rotating
body with a magnetic field):  a rotational pole and a magnetic pole.  The
North and South rotation poles lie along the spin axis of a body.  Like most
"units" (okay, I know these aren't *really* units -- that belongs to latitude
and longitude -- but I'm trying to be general here) these became defined
through convention.  Sorta like the all-powerful "right-hand-rule" in physics.
So yes, if you look "down" (we all know concepts like up and down are quite
arbitrary in space) on the Earth to the South pole, the planet spins clockwise.
This does NOT mean that the North pole rotates counter-clockwise.  If the
Earth weren't solid (stick Balana Tores -- pardon the spelling -- on THAT
problem) and we could see through to the North pole from the same vantage
point, it TOO spins clockwise.  If we switched to sit "above" the North pole,
and looked "down" on the planet, then it would look like the planet rotates
counter-clockwise.  Our convention, then, is that we apply our compass
directions to the rest of the planets.  
	Now the magnetic pole is not necessarily the same as the rotational
poles -- the alignment of the two differs for each planet/moon.  The
magnetic pole depends on the core of the body -- typically a molten liquid
metal.  From Earth's geological history, we know that the magnetic poles
are not stationary; there have been points when the North and South magnetic
poles reversed directions!
	This is made even more interesting by a effect called precession, the
slow movement of the *rotational* access.  A good visualization of this is
a spinning top -- a top doesn't spin in a perfect, unwavering, vertical
orientation.  The rotational axis itself moves in a slow, small circle.  This
is true of spinning planets as well.  That's why Polaris hasn't always been
our North star, and won't be in several thousand years.
	Okay, so this hasn't been brief.  But to sum up:  there are two kinds
of poles, rotational and magnetic, which are not typically aligned exactly
and sometimes not even remotely.  So if you want to talk about direction in
reference to a pole, make sure you indicate which one.

> ~mark

-Beau
-- 
| Beau Bierhaus  ([email protected])                                       |

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