Earth's  magnetism   The Earth behaves as a huge bar magnet which is   believed to  be  due  to  electric  currents  generated  by radioactivity  in the Earth's molten outer core. The positions of the magnetic poles have been observed to vary with time.

The magnetic field due to Earth at any point on its surface is specified by three elements, the horizontal component of the magnetic field, the angle dip ( or inclination) and declination. The dip (d ) is the angle between the direction of Earth's magnetic field and the horizontal direction. The declination is the angle between the geographical and the magnetic meridian.

The Earth's magnetic field gives rise to an outer magnetic field , the magnetosphere which has doughnut shape. Streams of particles emitted by the sun known as the solar wind distorts the magnetosphere. It presses down the side facing the sun and stretches out on the other side (see also aurora).