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According to this site Magnetic North, Geomagnetic and Magnetic Poles

The Geomagnetic poles (dipole poles) are the intersections of the Earth's surface and the axis of a bar magnet hypothetically placed at the center the Earth by which we approximate the geomagnetic field. There is such a pole in each hemisphere, and the poles are called as "the geomagnetic north pole" and "the geomagnetic south pole", respectively. On the other hand, the magnetic poles are the points at which magnetic needles become vertical. There also are "the magnetic north pole" and "the magnetic south pole".

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But why does the compass needle not point to the geomagnetic pole? I mean why aren't they both at the same location?

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Earth's magnetic field isn't really a dipole, but a dynamic field due to the convection occurring in the planet's core (consists of molten iron). The model below shows a simulation of the magnetic field (blue is pointing towards the core while yellow points away), the cluster of curves in the middle is the planet's core.

enter image description here

The geomagnetic pole is the location of the pole if earth's magnetic field were a simple dipole (no convection-driven fields).

Note also that, in your image, the geomagnetic pole hasn't moved much in the last century while the magnetic pole has. This is because every several thousand years, the magnetic poles flip sides (a non-constant rate of reversal, so we can't really say a definitive time-frame).

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  • $\begingroup$ are they usually in close proximity to each other? $\endgroup$ – erotavlas Mar 23 '14 at 17:36
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    $\begingroup$ Sometimes. During a reversal, they're not usually anywhere near each other (the pole was once in Oregon (but long before) it was Oregon). $\endgroup$ – Kyle Kanos Mar 23 '14 at 18:02
  • $\begingroup$ Which one are geomagnetic phenomena centered around, like for example aurora? $\endgroup$ – erotavlas Mar 23 '14 at 18:06
  • $\begingroup$ I believe that the aurorae are located near the geomagnetic pole, but I'm not entirely certain of that. $\endgroup$ – Kyle Kanos Mar 23 '14 at 18:09
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    $\begingroup$ Another way to say this is that the geomagnetic poles are by definition required to be antipodal (it's the best fit to a dipolar field.) The observed magnetic poles are not so required. $\endgroup$ – Mark Rovetta Mar 24 '14 at 19:19

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