Magnetic Pole

I

Introduction

Magnetic Pole, either of two locations on the surface of the earth where the direction of the earth’s magnetic field is vertical. The earth’s magnetic field is an area surrounding the earth in which objects experience an electromagnetic force. The direction of the force is the same as the direction of the magnetic field (see Magnetism: The Magnetic Field). At the north magnetic pole, the magnetic force of the earth’s magnetic field is downward, into the ground, and at the south magnetic pole, the magnetic force is upward, out of the ground. At most other locations on the surface of the earth, the earth’s magnetic field has a horizontal component and points toward the ground or away from it at an angle.

The orientation of the earth’s magnetic field at any location can be observed by suspending a bar magnet from a string so that the bar magnet is free to rotate. The magnet will align itself with the direction of the earth’s magnetic field. The angle that the magnetic field makes with the horizon is called the magnetic dip. For this reason, the magnetic pole is sometimes called the dip pole or the magnetic dip pole.

The earth’s magnetic poles can be located using a compass. A compass is a small bar magnet, called a needle, suspended such that it is free to rotate in the horizontal plane but not in the vertical plane. The north magnetic pole is located by following the north-pointing end of the compass needle, the south magnetic pole by following the south-pointing end of the compass needle. At a magnetic pole, the magnetic field is vertical and the compass needle does not indicate any particular direction along the ground. From any point on earth, a compass can be followed to the north and south magnetic poles.

II

Causes of the Earth’s Magnetic Field

Scientists still do not know exactly what causes the earth’s magnetic field. In the 16th century, it was believed that a mountain of magnetite (a magnetic mineral) was located at the North Pole and that this mountain caused the earth’s magnetic field. English physician William Gilbert was the first to propose, in 1600, that the earth itself was a massive magnet. Current theories hold that the earth’s magnetic field is created by currents within the liquid outer core of the earth, which is composed mostly of iron. This liquid core contains ions, or electrically charged atoms and molecules. The motion of these charged particles within the earth is thought to create the earth’s magnetic field. (See also Earth: The Core and Earth's Magnetism)

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III

Location of Magnetic Poles

The magnetic poles are located at considerable distance from the geographic poles, which are the ends of the axis that the earth revolves around. The north magnetic pole is situated in the vicinity of Ellef Ringnes Island in northern Canada, about 1300 km (about 800 mi) from the North Pole. The south magnetic pole is located just off of the coast of Wilkes Land, Antarctica. It is 2550 km (1600 miles) from the geographic South Pole.

The earth’s magnetic field is not perfectly symmetrical, but is wavy and somewhat irregular. Because of this irregularity, a compass some distance away from a magnetic pole may not point directly toward the magnetic pole; rather, the compass follows the direction of the earth’s magnetic field at that location. The path created by following the compass in the direction of the poles may be wavy, but it will end at a magnetic pole. Most maps indicate the directions of both true north, meaning the direction of the geographic north pole, and magnetic north, the direction in which a compass points. The difference in angle between the direction of true north and magnetic north at any given point on a map is known as the declination. Knowledge of magnetic declination is critically important when navigating with a compass and a map.

IV

Location of Geomagnetic Poles

Scientists sometimes find it easier to model the earth’s magnetic field as if it were a perfectly symmetrical magnetic field coming from one large bar magnet. The poles of this hypothetical magnetic field, based on averaging the direction and strength of earth’s magnetic field, are called the geomagnetic poles. The north geomagnetic pole is located near Thule, Greenland, 1250 km (780 miles) from the geographical North Pole. The south geomagnetic pole is located near Vostok, Antarctica, 1250 km (780 miles) from the geographic South Pole.

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