See also: Introduction

The Magnetic Poles should not be confused with two other types of poles that are related to the magnetic field. This multiplicity of poles arises from the fact that the Earth's magnetic field is, to a first approximation, that of a dipole, and for some applications a dipole approximation of some sort is adequate. The positions of these other poles are not determined by direct observation, but can be calculated from magnetic reference field models such as the International Geomagnetic Reference Field (IGRF).

Geomagnetic Poles:

The Geomagnetic Poles, sometimes referred to as the Geomagnetic Dipole Poles are the two points on the Earth's surface formed by the axis of an inclined dipole placed at the centre of the Earth. Because the dipole is centred, the Geomagnetic Poles are situated exactly opposite each other. However, the observed magnetic field is not vertical at the Geomagnetic Poles. The North Geomagnetic Pole position can be calculated from the first three coefficients of the IGRF or some other reference field model.

where and are the latitude and longitude of the north geomagnetic pole and ₁⁰, ₁¹, h₁¹ represent the first three coefficients of a magnetic reference field model.

Eccentric Poles:

A better dipole approximation of the Earth's magnetic field can be obtained by moving the inclined dipole away from the centre of the Earth by a distance that is, at present, approximately 530 km. The points at which the axis of this off-centre dipole cuts the Earth's surface are called the Eccentric Poles, or sometimes the Eccentric Axis Dipole Poles. The locations of the North and South Eccentric Poles, which are not opposite each other, can be calculated from the first eight coefficients of the IGRF. (See Arcticle by Fraser-Smith). Note that the magnetic field is not vertical at the eccentric poles.

Magnetic Poles:

The Magnetic Poles, sometimes called, as the Magnetic Dip Poles, are the points on the Earth's surface at which the magnetic field is directed vertically downward (north) or upward (south). Alternatively, inclination (also known as dip)is ±90° and horizontal intensity is zero. The Magnetic Poles are observable; it is possible to make observations in the vicinity of one of the Magnetic Poles from which its location can be determined. This is periodically done for both poles, more regularly and frequently for the North Magnetic Pole. It is also possible to estimate the position of the Magnetic Poles from a magnetic reference field model such as the IGRF . The positions calculated from the IGRF will differ from the observed positions, but the differences are relatively small.