Sunday 15 July 2012

MAGNET NORTH POLE AND SOUTH POLE

North Magnetic Pole

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"Magnetic North" redirects here. For other uses, see Magnetic North (disambiguation).


Part of the Carta Marina of 1539 by Olaus Magnus, depicting the location of magnetic north vaguely conceived as "Insula Magnetu[m]" (Latin for "Island of Magnets") off modern day Murmansk. The man holding the rune staffs is the Norse hero Starkad.
The North Magnetic Pole is the point on the surface of Earth's Northern Hemisphere at which the planet's magnetic field points vertically downwards.
The North Magnetic Pole moves over time due to magnetic changes in the Earth's core.[1] In 2001, it was determined by the Geological Survey of Canada to lie near Ellesmere Island in northern Canada at 81.3°N 110.8°W. It was situated at 83.1°N 117.8°W in 2005. In 2009, while still situated within the Canadian Arctic territorial claim at 84.9°N 131.0°W,[2] it was moving toward Russia at between 34 and 37 mi (55-60 km) per year.[3] As of 2012, the pole is projected to have moved beyond the Canadian Arctic territorial claim to 85.9°N 147.0°W.[2]
Its southern hemisphere counterpart is the South Magnetic Pole. Since the Earth's magnetic field is not exactly symmetrical, the North and South Magnetic Poles are not antipodal: i.e., a line drawn from one to the other does not pass through the geometric centre of the Earth.
The Earth's North and South Magnetic Poles are also known as Magnetic Dip Poles, with reference to the vertical "dip" of the magnetic field lines at those points.[4]

Contents

Introduction

See also: Magnet#Pole naming conventions
The North Magnetic Pole is the point where the Earth's magnetic field points downward; in other words, if a magnetic compass needle is allowed to rotate about a horizontal axis, it will point straight down when it is over the North Magnetic Pole. There is only one location where this occurs, near (but distinct from) the Geographic North Pole and the Geomagnetic North Pole.
All magnets have two poles that are distinguished by the direction of the magnetic flux. These poles could have any names, for example, "+" and "−"; but the convention in early compasses was to call the end of the needle pointing to the 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"). Because opposite poles attract, this definition implies that the Earth's North Magnetic Pole is a magnetic south pole and the Earth's South Magnetic Pole is a magnetic north pole. [5][6]

History

Early European navigators believed that compass needles were attracted either to a "magnetic mountain" or "magnetic island" somewhere in the far north (see Rupes Nigra), or to the Pole Star.[7][8] The idea that the Earth itself acts as 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 the Earth's magnetic field points vertically downwards. This is the definition used nowadays, though it would be several hundred years before the nature of the Earth's magnetic field was understood properly.[7]

Expeditions and measurements

See also: Arctic exploration, Farthest North, and List of Arctic expeditions

Early

The first expedition 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. Roald Amundsen found the North Magnetic Pole in a slightly different location in 1903. The third observation 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 in 1947.[9]

Project Polaris

At the onset of the Cold War, the U.S. War Department recognized a need for a comprehensive knowledge of the North American Arctic and asked the Army to undertake the task. An assignment was made in 1946 for the newly formed Army’s Air Corps Strategic Air Command to explore the entire Arctic Ocean area. The exploration was conducted by the 46th (later re-designated the 72nd) Photo Reconnaissance Squadron and reported on as a classified Top Secret mission named Project Nanook. This project in turn was divided into a multitude of identically classified projects one of which was Project Polaris. This special project was tasked to make a radar, photographic (trimetrogon, or three-angle, cameras) and visual study of the entire Canadian Archipelago. A Canadian officer observer was assigned to accompany each flight.
Charged with directing Project Polaris was its navigation leader, 1st Lt. Frank O. Klein, a World War II combat veteran. Incidental to the project and taken up at his own initiative was a study of northern terrestrial magnetism. The study was prompted by the surprise that the fluxgate compass did not behave erratically as expected by the authorities. It oscillated no more than 1 to 2 degrees over much of the region.[10][11] With the cooperation of many of his squadron teammates in obtaining many hundreds of statistical readings, startling results were revealed. For one, the center of the north magnetic dip pole was on Prince of Wales Island some 250 miles NNW of the positions determined by Amundsen and Ross.
Also astonishing was the revelation that the dip pole occupied a larger elliptical area with foci about 250 miles apart on Boothia Peninsula and Bathurst Island. Klein called the two foci local poles for their importance to navigation in emergencies when using a “homing” procedure. Soon (about 3 months) after Klein’s findings were officially reported, a Canadian ground expedition was sent into the Archipelago to locate the position of the magnetic pole. In a letter to 1st Lt. Frank Klein dated 21 July 1948 from R. Glenn Madill, Chief of Terrestrial Magnetism, Department of Mines and Resources, Canada, he wrote, “…we can agree on one point, and that is the presence of what we can call the main magnetic pole on northwestern Prince of Wales Island. I have accepted as a purely preliminary value, the position Latitude 72 degrees N and 100 degrees Longitude West. Your value of 73 degrees 15' and 99 degrees 45’ W is in excellent agreement, and I suggest you use your value by all means." (The positions were less than 20 miles apart.)[12]

Modern (post 1996)

The movement of Earth's north magnetic pole across the Canadian arctic, 1831–2001.
The Canadian government has made several measurements since, which show that the North Magnetic Pole is moving continually northwestward. In 1996 an expedition certified its location by magnetometer and theodolite at 78°35.7′N 104°11.9′W.[13] Its estimated 2005 position was 82.7°N 114.4°W, to the west of Ellesmere Island in Canada.[14] During the 20th century it moved 1100 km, and since 1970 its rate of motion has accelerated from 9 km/year to approximately 41 km/year, or 1.3 mm/sec (2001–2003 average; see also Polar drift).
This general movement is in addition to a daily or diurnal variation in which the North Magnetic Pole describes a rough ellipse, with a maximum deviation of 80 km from its mean position.[15] This effect is due to disturbances of the geomagnetic field by charged particles from the Sun.
North Magnetic Pole[16] (2001) 81.3°N 110.8°W (2004 est) 82.3°N 113.4°W (2005 est) 82.7°N 114.4°W
South Magnetic Pole (1998) 64.6°S 138.5°E (2004 est) 63.5°S 138.0°E (2007) 64.497°S 137.684°E[17]
The first team of novices to reach the Magnetic North Pole did so in 1996, led by David Hempleman-Adams. It included the first British woman and first Swedish woman to reach the Pole. The team also successfully tracked the location of the Magnetic North Pole on behalf of the University of Ottawa.
The biennial Polar Race takes place between Resolute Bay in northern Canada and the 1996-certified location of the North Magnetic Pole at 78°35.7′N 104°11.9′W.[citation needed] On 25 July 2007, the Top Gear Polar Challenge Special was broadcast on BBC Two in the United Kingdom, in which Jeremy Clarkson and James May became the first people in history to reach this location in a car.[18]

Magnetic north and magnetic declination

Magnetic declination from true north in 2000.
Main article: Magnetic declination
The direction 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 the 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 legends so that the direction of true north can be determined from north as indicated by a compass.
Magnetic declination has been measured in many countries, including the U.S. The line of zero declination (the agonic line) in the U.S. runs from the North Magnetic Pole through Lake Superior and southward into the Gulf of Mexico. Along this line, true north is the same as magnetic north. West of the line of zero declination, a compass will give a reading that is east of true north. Conversely, east of the line of zero declination, a compass reading will be west of true north.
Magnetic declination is still very important for certain types of navigation that have traditionally made much use of magnetic compasses; see Magnetic declination for details.

North Geomagnetic Pole

Main article: Geomagnetic pole
As a first-order approximation, the Earth's magnetic field can be modelled as a simple dipole (like a bar magnet), tilted about 10° with respect to the Earth's rotation axis (which defines the Geographic North and Geographic South Poles) and centered at the Earth's centre. The North and South Geomagnetic Poles are the antipodal points where the axis of this theoretical dipole intersects the Earth's surface. If the Earth's magnetic field were a perfect dipole then the field lines would be vertical at the Geomagnetic Poles, and they would coincide with the Magnetic Poles. However, the approximation is imperfect, and so the Magnetic and Geomagnetic Poles lie some distance apart.[19]
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 south magnetic pole. It is the centre of the region of the magnetosphere in which the Aurora Borealis can be seen. As of 2005 it was located at approximately 79.74°N 71.78°W, off the northwest coast of Greenland,[19] but it is now drifting away from North America and toward Siberia.

Geomagnetic reversal

Main article: Geomagnetic reversal
Over the life of the Earth, the orientation of Earth's magnetic field has reversed several 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 out of the mantle the magnetic particles contained within it are oriented in the direction of the magnetic field at the time the magma cools and solidifies.

See also

Notes and references

  1. ^ Merrill, Ronald T.; McElhinny, Michael W.; McFadden, Phillip L. (1996). "Chapter 8". The magnetic field of the earth: paleomagnetism, the core, and the deep mantle. Academic Press. ISBN 978-0-12-491246-5.
  2. ^ a b World Data Center for Geomagnetism, Kyoto. "Magnetic North, Geomagnetic and Magnetic Poles". Retrieved 2012-07-03.
  3. ^ North Magnetic Pole Moving East Due to Core Flux, National Geographic, December 24, 2009
  4. ^ "The Magnetic North Pole". Ocean bottom magnetology laboratory. Woods Hole Oceanographic Institution. Retrieved June 2012.
  5. ^ Serway, Raymond A.; Chris Vuille (2006). Essentials of college physics. USA: Cengage Learning. p. 493. ISBN 0-495-10619-4. Retrieved 2012-04-19.
  6. ^ Russell, Randy. "Earth's Magnetic Poles". Windows to the Universe. National Earth Science Teachers Association. Retrieved 2012-04-19.
  7. ^ a b Early Concept of the North Magnetic Pole, Natural Resources Canada, retrieved June 2007
  8. ^ The Geodynamo, D R Fearn, University of Glasgow, August 19, 2004
  9. ^ History of Expeditions to the North Magnetic Pole, Natural Resources Canada
  10. ^ White, Ken (1994). World in Peril: The Origin , Mission & Scientific Findings of the 46th / 72nd Reconnaissance Squadron (2nd revised ed.). K. W. White & Associates. ISBN 978-1883218102.
  11. ^ Wack, Fred John (1992). The Secret Explorers: Saga of the 46th/72nd Reconnaissance Squadrons. Seeger's Print.
  12. ^ The Citation to accompany the military award of the Legion of Merit to Klein reads: “ First Lt. Frank O. Klein distinguished himself by exceptionally meritorious conduct in the performance of outstanding services to the United States as a navigator while assigned to the 42nd and 72nd Reconnaissance Squadrons from June 1946 to October 1949. During this period, the exemplary ability, diligence and devotion to duty of Lieutenant Klein were instrumental factors in the resolution of many complex problems of major importance to the United States. He instigated research, which established that the magnetic north pole was not at the location reported in textbooks and on maps and charts at that time. His research not only revealed a new magnetic north pole position, but also revealed the existence of additional so-called secondary or local magnetic poles. The superior initiative, outstanding leadership, and personal endeavor displayed by Lieutenant Klein reflect great credit upon himself and the United States Air Corps."
  13. ^ 1996 Certified Position of the Magnetic North Pole, Jock Wishart, Polar Race organiser
  14. ^ North Magnetic Pole, Natural Resources Canada, retrieved May 2007
  15. ^ Geomagnetism — Daily Movement of the North Magnetic Pole, Natural Resources Canada
  16. ^ "Geomagnetism, North Magnetic Pole". Geological Survey of Canada. Natural Resources Canada. Archived from the original on 2010-03-26. Retrieved 11 January 2009.
  17. ^ "Poles and Directions". Australian Antarctic Division. 2011. Retrieved October 2011.
  18. ^ "Polar Challenge". Top Gear. 25 July 2007. 0:22 minutes in. BBC Two. Retrieved 19 April 2012.
  19. ^ a b "Geomagnetism Frequently Asked Questions". National Geophysical Data Center. Retrieved 19 April 2012.

    South Magnetic Pole

    From Wikipedia, the free encyclopedia
    Jump to: navigation, search
    Locations of South Magnetic Pole from direct observation and model prediction.[1]
    For additional general information about the Earth's magnetic poles, see North Magnetic Pole.
    The South Magnetic Pole is the wandering point on the Earth's Southern Hemisphere where the geomagnetic field lines are directed vertically upwards. It should not be confused with the lesser known South Geomagnetic Pole described later.
    For historical reasons, the "end" of a magnet that points (roughly) north is itself called the "north pole" of the magnet, and the other end, pointing south, is called magnet's "south pole". Because opposite poles attract, the Earth's South Magnetic Pole is physically actually a magnetic north pole (see also North Magnetic Pole – Polarity).
    The South Magnetic Pole is constantly shifting due to changes in the Earth's magnetic field. As of 2005 it was calculated to lie at 64°31′48″S 137°51′36″E,[2] just off the coast of Adelie Land, French Antarctica. That point lies outside the Antarctic Circle. Due to polar drift, the pole is moving north west by about 10 to 15 kilometers per year.
    North Magnetic Pole[3] (2001) 81.3°N 110.8°W (2004 est) 82.3°N 113.4°W (2005 est) 82.7°N 114.4°W
    South Magnetic Pole (1998) 64.6°S 138.5°E (2004 est) 63.5°S 138.0°E (2007) 64.497°S 137.684°E[4]
    <a href='http://oadsrv.com/www/delivery/afr.php?zoneid=119&cb=8341' target='_blank'><img src='http://oadsrv.com/www/delivery/afr.php?zoneid=119&cb=452&n=adc4e6a8' border='0' alt='' /></a>

    Contents

    Expeditions

    Early unsuccessful attempts to reach the South Magnetic Pole included those of French explorer Dumont d'Urville (1837–40), American Charles Wilkes (expedition of 1838–42) and Briton James Clark Ross (expedition of 1839–43).[5]
    On 16 January 1909 three men (Douglas Mawson, Edgeworth David, and Alistair Mackay) from Sir Ernest Shackleton's Nimrod Expedition claimed to have found the South Magnetic Pole,[6] which was at that time located on land. However, there is now some doubt as to whether their location was correct.[7]
    The approximate position of the pole on 16 January 1909 was 72.25°S 155.15°E.[8]

    Fits to global data sets

    The South Magnetic Pole has also been estimated by fits to global sets of data such as the World Magnetic Model (WMM) and the International Geomagnetic Reference Model (IGRF).[1] For earlier years back to about 1600, the model GUFM1 is used, based on a compilation of data from ship logs.[9]

    South Geomagnetic Pole

    Main article: Geomagnetic pole
    The Earth's geomagnetic field can be approximated by a tilted dipole (like a bar magnet) placed at the center of the Earth. The South Geomagnetic Pole is the point where the axis of this best-fitting tilted dipole intersects the Earth's surface in the southern hemisphere. As of 2005 it was calculated to be located at 79.74°S 108.22°E,[10] near the Vostok Station. Because the field is not an exact dipole, the South Geomagnetic Pole does not coincide with the South Magnetic Pole. Furthermore, the South Geomagnetic Pole is wandering for the same reason its northern magnetic counterpart wanders.


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