- Describe the structure and nature of the solar wind.
- Describe the nature and discovery of the Van Allen Belts.
- Explain how aurorae are caused.
- Describe aurorae and recall from where on Earth they are most likely to be observed

Solar Wind

The solar wind is a flow of charged protons and electrons flowing outward from the Sun. They can reach a velocity of 400 km per second. These particles escape the gravity of the Sun because they have too much energy.

The Solar wind has many effects in the Solar System, notably producing tails on comets and aurorae at the poles of certain planets.


Van Allen Belts

Imagine the Earth as a magnet, producing a magnetic field surrounding it. This is caused by Earth’s large iron core and the rotation of the Earth.

This field is called the Magnetosphere. This extends in the direction of the Sun but much further in the opposite direction, even further than the distance to the Moon. It deflects the damaging effects of the solar wind. Some of these charged particles get trapped in two belts of magnetism called the Van Allen Belts.

The outer belt is located 5,000 to 6,000 km from the Earth and contains electrons from the Sun. The inner belt is located between 1,000 to 3,000 km away and contains trapped protons.

They are named after Dr James Van Allen who discovered them in 1958.



The particles that get caught in the Van Allen Belts then move along these field lines toward the magnetic north and south poles and observers in these location witness aurorae.

These are spectacular displays of light and colour in the sky. In the northern hemisphere this is called Aurorae Borealis. In the southern hemisphere this is Aurora Australis.

The intensity of the aurorae depends on the ferocity of the solar wind which in turn depends on the level of solar activity.

They are best seen nearer the magnetic poles, near the (ant)arctic circles and near the equinox (March and September) although some sightings have been reported as far south as the north of Scotland.


Animation New Window

Animation Solar Wind

Image New Window

Links New Window

University of Colorado - Boulder Van Allen Belts - Laboratory for Atmosphere & Space Physics

Earth's magnetosphere, Van Allen Belts & aurorae Relationship between the three

Welcome to AuroraWatch UK Where to find Aurora

FusEdWeb: Fusion Energy Educational Web Site Solar wind


Explain the influence of the solar wind on Planet Earth.
Explain the influence of the solar wind on the Van Allen Belts.

Where on Earth are Aurorae most likely to be seen?
What causes Aurorae?

Did you know?

The Sun is classed as an ordinary G2 medium sized yellow dwarf star.


The interaction of the solar wind on Earth's magnetc field causes aurorae at northern and southern latitudes.