![]() Taken together, these cells generate the overall magnetic field, with smaller whorls and eddies creating local anomalies. ![]() It is believed that the earth's magnetic field is produced at depth by material of the earth's core slowly rotating in giant convection cells, so our central magnet is not a static thing. This deflection changes slowly over the years in amounts significant enough to warrant notation on topographic maps. Over most of Alaska, the direction in which a compass needle points is between 20 and 30 degrees east of true north. It is necessary to say "now" because, to complicate matters, the magnetic field lines are gradually changing their orientation. For practical purposes the problem can be treated as if a north magnetic pole now lay somewhere in the vicinity of Canada's Prince of Wales Island, near 75 degrees north latitude, 101 degrees west longitude. Compass needles align themselves with the field lines produced by the "central magnet". Put another way, the field lines in the area around a pole rise straight up, curve to pass over the equator horizontally, and plunge back into the earth in an area that can be interpreted as the opposite pole. The earth's magnetic poles are not centers of attraction at all, but simply blurry localities at which the field lines arising from the hypothetical magnet at the center happen to emerge perpendicular to the earth's surface. The external magnetic field of the earth is the same as that which would surround an inert sphere having a very small and powerful bar magnet at its center. This is true because the earth behaves as if the source of its magnetism was concentrated at its center. In fact, there is no particular point that can be identified as the north (or south) magnetic pole. It is a common misconception that the needle of a magnetic compass points to a particular spot on the earth's surface.
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