Magnetic North

Magnetic North is one of several locations on the Earth's surface known as the "North Pole". Its definition, as the point where the geomagnetic field points vertically downwards, i.e. the dip is 90°, was proposed in 1600 by Sir William Gilbert, a courtier of Queen Elizabeth I, and is still used. It should not be confused with the less frequently used Geomagnetic North Pole. Magnetic North is the place to which all magnetic compasses point, although since the pole marked "N" on a bar magnet points north, and only opposite magnetic poles are attracted to each other, the Earth's magnetic north is actually a south magnetic pole.

The first expedition to reach this pole was led by James Clark Ross, who found it at Cape Adelaide on the Boothia Peninsula in 1831. Roald Amundsen found Magnetic North in a slightly different location in 1903. The third observation of Magnetic North was by Canadian government scientists Paul Serson and Jack Clark, of the Dominion Observatory, who found the pole at Allen Lake on Prince of Wales Island. The Canadian government has made several measurements since, which show that Magnetic North is continually moving northwest. Its average speed between 2001 and 2003 was about 40 km per year.

This movement is on top of a daily or diurnal variation in which Magnetic North describes a rough ellipse, with a maximum deviation of 80 km from its mean position. This effect is due to disturbances of the geomagnetic field by the sun.

The angular difference between Magnetic North and true North varies with location, and is called the magnetic declination.