A cross-section of the Earth showing the outer core and the orientation of the magnetic field. A pole representing the magnetic field axis wanders around and flips.

The Earth's magnetic field is produced by the motions of molten iron in the Earth's core - in effect a giant dynamo. While the true North and South poles represent the geographic points around which the Earth rotates, the magnetic poles are the projection onto the surface of the axis of the Earth's magnetic field.

The axis of the field wanders around and is currently at an angle of 11 degrees away from the axis of rotation. The local magnetic deviation from True North is marked on navigational charts, together with the annual adjustment due to wander. The magnetic signature of rocks on the seafloor indicates that the direction of the field (its polarity) has reversed approximately every half million years. The last reversal was 780,000 years ago, so we are now overdue for a flip.

Data source: Planetary Visions Satellite Imagemap.

Credit : Planetary Visions Ltd.