Magnetic north
The north magnetic pole is a point on the surface of Northern Hemisphere at which the Earth's magnetic field points vertically downward (in other words, if a magnetic compass needle is allowed to rotate in three dimensions, it will point straight down). There this occurs, near (but distinct from) the geographic north pole.
The north magnetic pole moves over time according to magnetic changes in the Earth's outer core.
- 2001 - Magnetic north was found to lie west of Ellesmere Island in Canada at 81° 18' N| 110° 48' W.
- 2009 - it was situated within the Canadian Arctic at 84°54'N 31°00' W.
It was moving toward Russia at between 55 and 60 km per year.[1] By 2021, the pole is projected to have moved beyond the Canadian Arctic to 86.40°N 156.786°E.
Its southern hemisphere counterpart is the south magnetic pole. Since Earth's magnetic field is not exactly symmetric, the north and south magnetic poles are not antipodal, meaning that a straight line drawn from one to the other does not pass through the centre of the Earth.
Polarity
All magnets have two poles, where the lines of magnetic flux enter and emerge. By analogy with Earth's magnetic field, these are called the magnet's "north" and "south" poles. The convention in early compasses was to call the end of the needle pointing to Earth's north magnetic pole the "north pole" (or "north-seeking pole") and the other end the "south pole" (the names are often abbreviated to "N" and "S").
The direction of magnetic field lines is defined such that the lines emerge from the magnet's north pole and enter into the magnet's south pole.
History
Early European navigators, cartographers and scientists believed that compass needles were attracted to a hypothetical "magnetic island" somewhere in the far north, or to Polaris, the pole star.[2] The idea that Earth itself acts as essentially a giant magnet was first proposed in 1600, by the English physician and natural philosopher William Gilbert. He was also the first to define the north magnetic pole as the point where Earth's magnetic field points vertically downwards. This is the current definition, though it would be a few hundred years before the nature of Earth's magnetic field was understood with modern accuracy and precision.[2]
First observations
The first group to reach the north magnetic pole was led by James Clark Ross, who found it at Cape Adelaide on the Boothia Peninsula on June 1, 1831, while serving on the second arctic expedition of his uncle, Sir John Ross. Roald Amundsen found the north magnetic pole in a slightly different location in 1903. The third observation was by Canadian government found the pole at Allen Lake on Prince of Wales Island in 1947.[3]
Modern (post-1996)
The Canadian government has made several measurements since, which show that the north magnetic pole is moving continually north-westward.
This general movement is in addition to a daily variation in which the north magnetic pole describes a rough ellipse, with a maximum deviation of 80 km from its mean position.[4] This effect is due to disturbances of the geomagnetic field by charged particles from the Sun.
Magnetic north and magnetic declination
Historically, the magnetic compass is an important tool for navigation. While it has been widely replaced by Global Positioning Systems (GPS) many aeroplanes and ships still carry them, as do sailors and hikers.
The direction in which a compass needle points is known as magnetic north. In general, this is not exactly the direction of the north magnetic pole (or of any other consistent location). Instead, the compass aligns itself to the local geomagnetic field, which varies in a complex manner over Earth's surface, as well as over time. The local angular difference between magnetic north and true north is called the magnetic declination. Most map coordinate systems are based on true north, and magnetic declination is often shown on map legend so true north can be determined from north as indicated by the compass.
North geomagnetic pole
The Earth's magnetic field can be explained as a simple bar magnet (dipole), tilted about 10° to Earth's axis of rotation. This axis of rotation is the 'geographic north' and geographic south poles). If Earth's magnetic field were a perfect dipole then the magnetic field line would coincide with the magnetic poles. However in the real world the magnetic and geomagnetic poles lie some distance apart.
Like the north magnetic pole, the north geomagnetic pole attracts the north pole of a bar-magnet and so is in a physical sense actually a magnetic south pole. It is the centre of the region where the Borealis can be seen. As of 2015 it was located at approximately over Ellesmere Island, Canada but it is now drifting away from North America and toward Siberia.
Geomagnetic reversal
Over the life of Earth, the orientation of Earth's magnetic field has reversed many times, with magnetic north becoming magnetic south and vice versa – an event known as a geomagnetic reversal. Evidence of geomagnetic reversals can be seen at mid-ocean ridges where tectonic plates move apart and the seabed is filled in with magma. As the magma seeps cools, and solidifies into igneous rock, it is imprinted with a record of the direction of the magnetic field at the time that the magma cooled.
References
- Adapted from the Wikipedia article
- ↑ North Magnetic Pole Moving East Due to Core Flux, National Geographic, December 24, 2009
- ↑ 2.0 2.1 Early Concept of the North Magnetic Pole, Natural Resources Canada, retrieved June 2007
- ↑ History of Expeditions to the North Magnetic Pole, Natural Resources Canada
- ↑ Geomagnetism – Daily Movement of the North Magnetic Pole, Natural Resources Canada
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