Geomagnetic pole

The geomagnetic poles are antipodal points where the axis of a best-fitting dipoleintersects the surface of Earth. This theoretical dipole is equivalent to a powerful bar magnet inside the Earth. The best-fitting dipole generally results from a theoretical magnet that is not precisely at the center of the Earth, this is known as the eccentric dipole model. For modern-day Earth (unlike most planets in our Solar System) a simpler centered dipole model is a close enough approximation to be used for some purposes. There are historical periods when the Earth's field did not resemble a dipole at all.

In contrast to the geomagnetic poles, the observed magnetic poles or dip poles of the Earth are places where the actual magnetic field intersects the surface. The magnetic poles are not antipodal: asymmetries in the earth and variations in its magnetic field mean that the line on which they lie does not pass through Earth's center.

Owing to the motion of fluid in the Earth's outer core, the magnetic field is constantly moving, in what is called geomagnetic secular variation. This leads to short-term changes in the magnetic and geomagnetic poles.

Although the geomagnetic poles average out local variations in the magnetic field, they are useful in geophysics as an efficient and more slowly-changing approximation than the magnetic poles. For example, since it is the entire field that determines the positions of auroras, the geomagnetic poles are an effective model for predicting their behavior.