A plane passing through the geographical poles(that is axis of rotation of the earth) and a given point P on the earth’s surface is called the geographical meridian at the point P. The plane passing through the geomagnetic poles (dipole axis of the earth) and the point P is called the magnetic meridian at the point P.
The angle between the magnetic meridian and the geographical meridian at a point is called the declination at that point.
Navigators use a magnetic compass needle to locate direction. The needle stays in equilibrium when it is in magnetic meridian. For finding the true north, navigators have to use declination and arrive at the direction of true north.
Chapter permanent magnets
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