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

[silveronthetree]

ANd to actually answer the questions the first link says this about the definition of a North Pole - if the planet is outside our solar system, the second paragraph applies.

The International Astronomical Union defines the geographic north pole of a planet or other object in the solar system as the planetary pole that is in the same ecliptic hemisphere as the Earth's North Pole. More accurately, "The north pole is that pole of rotation that lies on the north side of the invariable plane of the solar system".[1] This definition means that an object's axial tilt is always 90° or less, but its rotation period may be negative (retrograde rotation) – in other words, it rotates clockwise when viewed from above its north pole, rather than the "normal" counterclockwise direction exhibited by the Earth. Venus rotates in the opposite direction to the other planets, and Uranus has been knocked on its side and rotates almost perpendicular to the rest of the solar system.

Another common definition uses the right-hand rule to define an object's north pole: it is then the pole around which the object rotates counterclockwise.[2] With this definition, axial tilts may be greater than 90° but rotation periods are always positive.