Conceptual image showing the magnetic field that surrounds and penetrates the planet Earth. Magnetic field lines emerge from the south magnetic pole, bend overhead and converge at the north magnetic pole, which is offset from the geographic north pole by 11 degrees. The exact position of the magnetic poles, indicated by the yellow line, varies by about 15 km. The field, which closely resembles that of a bar magnet, is generated by the dynamo effect. Inside the Earth's outer core, convective heating causes cells of ionised metal to rise and fall in a circular motion. These act like gigantic electrical currents, which in turn generate the magnetic field in the same way that a current circulating in coils of wire does. The Earth's magnetic field has a strength at the poles of 60 microtesla (0.6 gauss), nearly 200 times weaker than the field of a domestic fridge magnet.