Phenomena related to the Earth’s magnetic field
The importance of the magnetic field to life on Earth
The Earth’s magnetic field is very important for humans and other animals on Earth because it protects us from being bombarded (hit) by high energy charged particles which are emitted by the Sun. The stream of charged particles (mainly positively charged protons and negatively charged electrons) coming from the sun is called the solar wind. When these particles come close to the Earth, they are deflected by the Earth’s magnetic field and cannot shower down to the surface where they can harm living organisms. Astronauts in space are at risk of being irradiated by the solar wind because they are outside the zones where the charged particles are trapped.
Visualisation of the magnetosphere
The region above Earth’s atmosphere in which charged particles are affected the Earth’s magnetic field is called the magnetosphere. Relatively often, in addition to the usual solar wind, the Sun may eject a large bubble of material (protons and electrons) with its own magnetic field from its outer atmosphere. Sometimes these bubbles travel towards the Earth where their magnetic fields can join with Earth’s magnetic field. When this happens a huge amount of energy is released into the Earth’s magnetosphere, causing a geomagnetic storm. These storms cause rapid changes in the Earth’s magnetosphere which in turn may affect electric and magnetic systems on the Earth such as power grids, cellphone networks, and other electronic systems.
Aurorae (pronounced Or-roar-ee)
Another effect caused by the Earth’s magnetic field is the spectacular Northern and Southern Lights, which are also called the Aurora Borealis and the Aurora Australis respectively.
When charged particles from the solar wind reach the Earth’s magnetosphere, they spiral along the magnetic field lines towards the North and South poles. If they collide with particles in the Earth’s atmosphere, they can cause red or green lights which stretch across a large part of the sky and which is called the aurora.
Aurora borealis photographed in Alaska
Aurora australis photographed from space
As this only happens close to the North and South poles, we cannot see the aurorae from South Africa. However, people living in the high Northern latitudes in Canada, Sweden, and Finland, for example, often see the Northern lights.