Cause of magnetic north
What causes magentic north?
The Earth, as we know, has a magnetic field. Like a bar magnet, it has
a magnetic north pole and a magnetic south pole. But these do not coincide
exactly with the Earth's geographic poles, which are the places on the
Earth through which the axis (the imaginary line around which the Earth
rotates) passes. Furthermore, the magnetic poles don't stay in one place;
they are observed to wander, currently about 0.15 degree westward per year.
The magnetic pole is not actually a point on the Earth's surface but
instead is a region where the magnetic field lines are perpendicular to the
surface of the Earth through which they pass. In 1970 the north magnetic
pole region was found to located at approximately latitude 76.2 degrees N
and longitude 101 degrees W, among the the arctic islands in northern
Canada. This being said, "magnetic north", which is the direction in which
the north-seeking pole of a compass points at any given location, is not
in general directly toward the magnetic north pole! The Earth's magnetic
field is much more complicated than that of a bar magnet; at a given
location a compass will generally point in a direction some degrees
east or west of "true north".
There is good evidence that the Earth's core is made up a liquid outer core
surrounding a solid inner core. It is believed that the Earth's magnetic
field is produced by electric currents in the liquid part of the core.
So the Earth is, in essence, a sort of electromagnet.
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Update: June 2012