Earth is a giant magnet. Scientists today speculate that the central or inner core of the globe is a solid sphere of mainly iron material, held in place by the pressure of the super heated, outer molten core. These in turn are surrounded by the earth’s mantle and crust.
It is postulated that the interplay between these two inner spheres at the centre of the earth act as something of a dynamo and that the resultant energy is a gigantic magnetic field which circulates through the earth’s centre and out again.
This geomagnetic field has been imaged as cycling from North to South with the weakest points being just above each of these Polar Regions where the magnetic fields enter the earth. This magnetic force called the magnetosphere, surrounds the earth, protecting life on the planet from the harmful rays of cosmic solar winds that constantly bombard the globe and would otherwise destroy.
The phenomenon known to us as the Auroras (Northern — Aurora Borealis, Southern -– Aurora Australis) are the resultant electromagnetic storms sparked as high energy particles carried by solar winds enter the earth’s atmosphere at these weak spots in the protective magnetosphere. It is these electric magnetic storms which cause the night skies to light up so exquisitely in the polar regions. (See more about this subject.)
However, the earth’s outer crust too is magnetized. It is covered with localized magnetic fields, the source of which is predominantly from earlier volcanic activity which leave iron deposits post eruption in the form of cold lava flows. In deed one method scientists have of dating and measuring the strength of the crusts magnetism is by analyzing these rocks.
A magnetic compass, therefore, aligns itself to these magnetic fields in a direction called magnetic north. True north, on the other hand is the direction from a given location to the north geographic pole. The angle of difference between magnetic north and true north is called magnetic declination.
Many people believe that a compass needle points at the North Magnetic Pole. This is not true; if you follow your compass needle you will eventually arrive at the North Magnetic Pole, but not by the most direct route.