North magnetic pole

The north magnetic pole, also known as the magnetic north pole, is a point on the surface of Earth's Northern Hemisphere at which the planet'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 is only one location where this occurs, near (but distinct from) the geographic north pole. The Earth's magnetic north pole is actually considered the "south pole" in terms of a typical magnet, meaning that the north pole of a magnet would be attracted to the Earth's magnetic north pole. The north magnetic pole moves over time according to magnetic changes and flux lobe elongation in the Earth's outer core. In 2001, it was determined by the Geological Survey of Canada to lie west of Ellesmere Island in northern Canada at 81°18′N 110°48′W. It was situated at 83°06′N 117°48′W in 2005. In 2009, while still situated within the Canadian Arctic at 84°54′N 131°00′W, it was moving toward Russia at between 55 and 60 km (34 and 37 mi) per year. In 2013, the distance between the north magnetic pole and the geographic north pole was approximately 800 kilometres (500 mi). As of 2021, the pole is projected to have moved beyond the Canadian Arctic to 86.400°N 156.786°E / 86.400; 156.786 (Magnetic North Pole 2021 est). 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 geometric center of Earth. 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.

Polarity All magnets have two poles, where lines of magnetic flux enter one pole and emerge from the other pole. By analogy with Earth's magnetic field, these are called the magnet's "north" and "south" poles. Before magnetism was well understood, the north-seeking pole of a magnet was defined to have the north designation, according to their use in early compasses. However, opposite poles attract, which means that as a physical magnet, the magnetic north pole of the Earth is actually on the southern hemisphere. In other words, if we establish that true geographic north is north, then what we call the Earth's north magnetic pole is actually its south magnetic pole since it attracts the north magnetic pole of other magnets, such as compass needles. 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 (see Rupes Nigra), or to Polaris, the pole star. 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.

Expeditions and measurements

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 1 June 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 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.

Project Polaris At the start of the Cold War, the United States Department of War recognized a need for a comprehensive survey of the North American Arctic and asked the United States Army to undertake the task. An assignment was made in 1946 for the Army Air Forces' recently formed 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 many separate, but identically classified, projects, one of which was Project Polaris, which was 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. Frank O. Klein, the director of the project, noticed that the fluxgate compass did not behave as erratically as expected—it oscillated no more than 1 to 2 degrees over much of the region—and began to study northern terrestrial magnetism. With the cooperation of many of his squadron teammates in obtaining many hundreds of statistical readings, startling results were revealed: The center of the north magnetic dip pole was on Prince of Wales Island some 400 km (250 mi) NNW of the positions determined by Amundsen and Ross, and the dip pole was not a point but occupied an elliptical region with foci about 400 km (250 mi) 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. About three 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. R. Glenn Madill, Chief of Terrestrial Magnetism, Department of Mines and Resources, Canada, wrote to Lt. Klein on 21 July 1948:

… we 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 73°N and longitude 100°W. Your value of 73°15'N and 99°45’W is in excellent agreement, and I suggest that you use your value by all means. (The positions were less than 30 km (20 mi) apart.)

Modern (post-1996)

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