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Auroras or Polar Lights

Blue, green, red. Twisting, diffuse or curtain-like, … . Auroras occur when the Earth’s magnetosphere traps or diverts the charged particles from the Sun. Subsequently, these particles move into the lower regions of the atmosphere along the magnetic field lines of the Earth.
When charged electrons from the solar wind collide with neutral particles in our atmosphere, the latter are so excited that they emit light. At some degrees of latitude, auroras are visible with the naked eye.

Auroras
Aurora. Credits Jan Curtis

This kind of phenomenon is particularly visible at the polar latitudes. The main part of the auroras occurs in the so-called auroral ovals, oval-shaped regions surrounding the Earth’s geomagnetic poles at a latitude between 12 and 22 degrees.


In particular, the Scandinavians can enjoy this spectacle in Europe, but also in Belgium, at about the 40th latitude from the North Pole, auroras may sometimes be seen. This is certainly the case for maximum solar activity.

 

The Secret of the Colours

The colour of auroras teaches us something about the chemical elements in our atmosphere that are excited by the particles of the solar wind. The “lines” of certain aurora types reflect the lines within the Earth’s magnetic field along which the protons and electrons in the solar plasma flow. The colour of the aurora depends on the altitude of the area in which particles are struck and on the energy of the struck particles.

  • Above an altitude of 200 kilometres, the aurora tends to colour red after atomic oxygen has been excited by the electrons in the solar plasma;
  • Between 100 and 200 kilometres of altitude, nitrogen is excited, emitting secondary electrons that interact with the oxygen. The sky colours blue and green then.
  • Below an altitude of 100 kilometers, nitrogens colour purple after they have been “excited” by the solar wind.

 

 

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