North Pole: Encyclopedia II - North Pole - Magnetic North

North Pole - 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 orientation of magnetic fields of planets can flip over, an event which is called a geomagnetic reversal. The Earth's poles have done this repeatedly throughout history, and 500,000 years ago, the south magnetic pole was at the South Pole. It is thought that this occurs when the circulation of liquid nickel/iron in the Earth's outer core is disrupted and then reestablishes itself in the opposite direction. It is not known what causes these disruptions.

The first expedition to reach this pole was led by James Clark Ross, who found it at Cape Adelaide on the Boothia Peninsula on June 1, 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 Astrophysical 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 location (in 2005) is 82°07' North, 114° 04' West, near Ellesmere Island, the biggest of the Queen Elizabeth Islands, in Canada. During the 20th century it has moved 1100 km, and since 1970 its rate of motion has accelerated from 9 km/year to 41 km/year (2001-2003 average; see also Polar drift). If it maintains its present speed and direction it will reach Siberia in about 50 years, but it is expected to veer from its present course and slow down.

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. A line drawn from one magnetic pole to the other does not go through the centre of the Earth, it actually misses it by about 530 km.

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

Adapted from the Wikipedia article "Magnetic North", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki