Geomagnetism
| Deep below the Earth's crust lies the mantle. The region beneath the mantle is called the core, and consists of two parts, a liquid outer part that is around 2,250 kilometers thick and a solid inner part 1,220 kilometers thick. The core is primarily made up of iron, with a small amount of nickel. The liquid iron in the outer core is particularly important, because it is the primary source of Earth's magnetic field. Unlike a common magnet, though, the north and south ends of our "global magnet" are not exactly situated at Earth's rotational poles. Instead, the magnetic north pole is actually situated in northern Canada (south of the North Pole), and the magnetic south pole actually resides north of Antarctica (home of the South Pole) and just south of Australia. Shown here is a "Global Magnetic Declination" false color map determined by the U.S. Department of Defense. Very rarely does a compass point to true north or south, and such a map is useful for resolving how "off" a compass is expected to be at any point on the globe. If you are in an area marked in yellow on the map, your compass needle would point almost exactly to "true north"; in areas marked pink or purple, your compass needle would point towards "true south." In green and blue areas, your compass points west of true north, and in orange and red areas, you compass points east of true north. The color code and the numbers refer to how many degrees east (+) or west (-) of true north your compass reads. |
Credit: Map by the United States Geological Society
For more info: http://geomag.usgs.gov/models.html