| The magnetic field of the Earth |
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In the same way as a magnet the Earth is surrounded by a large magnetic field. This is invisible to us. In fact, the magnetic field goes through us and most of what surrounds us without us noticing it.
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We may, however, notice the effects of the magnetic field. With modern instruments we may observe how particles from the Sun are being led through the field and how aurora borealis occurs around the magnetic poles. We may also measure the magnetic field and the variation of strength in it. |
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| Van Allen’s radiation belts |
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| The Van Allen’s belts near the Earth contain many charged particles from the Sun, which have been caught by the magnetic field. |
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Charged particles from cosmic radiation and from the Sun pour out towards the Earth. When they meet the magnetosphere, the Earth’s magnetic field prevents them from continuing straight ahead. Unless each individual particle has extremely high energy, they may only be let into the atmosphere at very high latitudes and only by following rather twisted orbits.
In certain areas round the Earth charged particles move in rather stable orbits. These radiation belts have a cross-section, which reminds us of crescents and contain rather a lot of charged particles.
The particles travel in spirals along the field lines and jump between the magnetic polar areas. They take from 0.1 – 0.3 seconds at moving between the poles!
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The Earth’s magnetic field.
Click on the picture in order to get a larger version. |
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The belts were discovered by some of the first satellites in 1958. The instruments in the satellites were partly destroyed by the surprisingly intense radiation.
Where the solar wind hits the magnetic field a shock front occurs. This may be compared with water from the tap. When the water hits the bottom of the washbasin, the water alters direction suddenly. This is called a shock!
The outer boarder of the magnetosphere is called the magnetopause. On the rearside of the Earth the magnetic field is stretched strongly out. In the field there are several types of currents, among others the so-called ring currents. |
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