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Tell Me More About the Magnetic Pole

By Larry Newitt
Geological Survey Of Canada Natural Resources Canada

Contrary to Captain Torvey's belief, the North Magnetic Pole is not a magnetic meteorite floating in the polar ice. What is it then? Most of you are familiar with a simple bar magnet. Magnetic field lines of force leave the magnet at one end, curve around, and enter the other end. The Earth behaves somewhat like a large bar magnet. The point where the magnetic field lines leave the Earth's surface pointing straight up is called the South Magnetic Pole; the point where thee magnetic field lines point straight down is the North Magnetic Pole. A compass points approximately north because its needle orients itself parallel to the magnetic field lines that flow between the southern and northern polar regions.

Of course the Earth's magnetic field is not produced by a simple bar magnet at its centre. Scientists believe that it is produced by electric currents generated by the movement of molten metal in the outer core of the Earth. This is a complex process, resulting in two interesting phenomena. First, the shape of the Earth's magnetic field is distorted, so that the north and south magnetic poles are not exactly opposite each other. The North Magnetic Pole is presently near Ellef Ringnes Island in the Canadian arctic islands. The South Magnetic Pole is just off the coast of Antarctica, approximately 3000 km due south of Tasmania. Second, the magnetic field is constantly changing, and this means that the magnetic poles are constantly in motion. In fact, since 1831 when Commander James Clark Ross first located it on the west coast of the Boothia Peninsula, the North Magnetic Pole has moved northwest almost 1000 km. Its current rate of motion is 15 km per year.

The magnetic poles also move because of distortions in the magnetic field caused by charged particles emitted by the Sun. These emissions result in the North Magnetic Pole moving in an irregular elliptical path around its "normal" position. Although compasses don't work very well close to the North Magnetic Pole, if you did have one that was functional you could watch its needle swing over the course of a day as the Magnetic Pole moved. It is probably this daily motion of the Pole that so intrigued and confounded Captain Torvey.


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An Access Excellence Science Mystery sponsored by Genentech, Inc.
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