Question Time!

[such_heights]

Calling my geologically inclined friends: please excuse a little lazy-webbing and help me resolve a debate with my father. Is there a non-arbritrary way of distinguishing a planet's north from its south, one that doesn't simply rely on convention? And if not, does that make all sci-fi talk of an unhabitated planet's southern hemisphere etc completely nonsensical?

... These are the things that keep me up at night.

Comments

[zahrawithaz.livejournal.com]

I'm only echoing others now, but yes, there are two types of pole--the axis on which the planet rotates, and the magnetic pole toward which the compass turns. The latter does reverse periodically, while the the former doesn't (though I suppose a big enough asteroid strike could jostle it).

I believe it's only happenstance that on Earth the two poles aren't that far off from each other, and that they could hypothetically be much farther apart on a planet with a different axial tilt; but someone may be able to correct me there.

[avendya]

I think that between the answer about the plane of the ecliptic and elsane, you have it covered, but I thought I should point out magnetic poles and geographic poles can also switch (so this is a really bad method of determining north and south on geologic time scales).

(C.f. The Guardian.)