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Magnetic North Pole

82° 42′ 0″ N, 114° 24′ 0″ W

Somewhere in Canada

Not only is the Magnetic North Pole difficult to get to, but it also moves over 10 kilometers per year, and it even moves in a rough oval as much as 80 kilometers each day. But it is roughly the spot to which compasses point when determining the direction “north.” Until GPS completely displaces compasses, for the purposes of navigation it’s important to know the location of the Magnetic North Pole and the lines of the Earth’s magnetic field (Figure 128-1).

Figure 128-1. The North Pole and Magnetic North Pole

The Earth rotates on its axis, at 23.5º to the perpendicular to the Earth’s orbit around the Sun. The axis passes through the Geographic North and South Poles. The location of the geographic poles sets the lines of longitude; latitude is measured from the Equator, which sits halfway between the poles. The axis and the poles are the basic reference points for navigation.

Unfortunately, compasses do not point to the Geographic North Pole, but instead follow the Earth’s magnetic field and point approximately toward the ever-moving Magnetic North Pole. To compensate for this problem when using a compass, it is necessary to know the declination. At any point on the Earth, the declination is the angle between a line drawn to the Geographic North Pole and the direction in which the compass is indicating north.

The Earth’s magnetic field can be approximated by imagining that the Earth contains a large bar magnet whose south pole points toward the Magnetic North Pole and whose north pole points toward the Magnetic South Pole. (In reality, the Magnetic North and South Poles are not diametrically opposite each other, and the Earth’s magnetic field is not even uniform across the Earth’s surface.)

The imaginary bar magnet is titled approximately 11º degrees from the Earth’s rotational axis. The south pole of this imaginary magnet points to a spot called the Geomagnetic North Pole, which is located near Greenland at 79.74° N, 71.78° W. But only about 90% of the Earth’s magnetic field can be approximated by a bar magnet—the other 10% causes the Earth’s magnetic field to vary by location and so the Magnetic North Pole and the imaginary Geomagnetic North Pole do not coincide.

Currently, the Magnetic North Pole is located in the far north of Canada. In 2001, it was found to be at 81.3°N, 110.8°W. When navigating north with a compass, a traveler will follow the lines of the Earth’s magnetic field, eventually arriving at the Magnetic North Pole, but not by the most direct route because of variations in the field. For this reason, the compass only approximately points to the Magnetic North Pole, and declination varies from place to place.

It is possible to reach both the Magnetic North Pole and the Geographic North Pole by starting in the far north of Canada at Resolute Bay in Nunavut. The Qausuittuq Inn at Resolute Bay has been the starting point for many such expeditions (ask there for directions!).

The truly hardy can enter the biannual Polar Race from Resolute Bay to the Magnetic North Pole.

Practical Information

The Qausuittuq Inn’s website is http://www.resolutebay.com/. The Polar Race can be found at http://polarrace.com/.

The Earth’s Magnetic Field

Although the Earth’s magnetic field may appear to come from a permanent bar magnet, it does not. Even though the center of the Earth contains iron, it is not permanently magnetized because it’s too hot. At a temperature called the Curie point, ferromagnetic materials lose their magnetism; for iron that happens at 768°C.

The Earth consists of four major layers: from outside to inside, these are the crust (on which we live), the mantle, the outer core, and the inner core (Figure 128-2). The inner core is believed to be mostly composed of iron at over 5,000ºC—well above the Curie point, preventing it from being a permanent magnet.

Figure 128-2. Earth’s layers

Surrounding the inner core is the outer core. The outer core is believed to be a liquid, hot alloy of nickel and iron. It’s the outer core that is thought to be the source of Earth’s magnetic field, and the motion of the outer core’s liquid explains the changing nature of the Earth’s magnetic field.

The liquid outer core apparently experiences a dynamo effect: as the liquid passes through the Earth’s magnetic field, a current is induced in the liquid metal; this current creates a magnetic field, which in turn induces a current in the moving liquid. In this way, the magnetic field is self-sustaining.

The outer core liquid is moving because of convection currents generated by the intensely hot inner core, and it moves relative to the surface of the Earth because of the Coriolis effect. The Coriolis effect is an apparent error in Newton’s laws of motion that occurs when the vantage point isn’t fixed.

For example, if a cannon ball is launched a long distance, directly northward along a meridian line, it will not land on the meridian line. This happens because the Earth rotates while the ball is in the air, and because the speed of the rotation depends on the latitude. These two factors mean that the ball falls to the east of the meridian line because its landing point is moving much more slowly than its launch point.

From the perspective of an Earthbound viewer, an unknown (and nonexistent) force appears to have deflected the ball from its straight path. This is called the Coriolis effect, and the nonexistent force is the Coriolis force.

The overall effect of these forces is that the liquid appears to create dynamos along a roughly north-south axis. These dynamos are responsible for the Earth’s magnetic field.