Northern Lights – Aurora Borealis

     

Northern lights, mostly called aurora, are the fluttering lights that can be observed in the sky over the northern-most parts of the world. A similar light is located over the southern-most parts of the world; it is called southern lights. Together the northern- and southern lights are called polar lights.

The Latin word for northern lights, Aurora Borealis, was first used in the early seventeenth century. Aurora was the goddess of dawn, i.e. red light of dawn, in ancient Roman mythology and Borealis means northerly. A translation would be the northerly light of dawn. The Latin word for southern lights is Aurora Australis, the southerly light of dawn. Also the Lappish word for auroras, guovsahas, is related to the light of dawn.

Beliefs in ancient times
Before people knew what they know today they tried, in their own way, to explain why there were auroras. People knew that there were auroras but they did not know why. At that time people were very superstitious so their explanations sometimes became very imaginative.

Three old Nordic explanations are mentioned in the book "Kongespeilet" from the thirteenth century. At that time people thought the Earth was flat and surrounded by oceans. One explanation was that the oceans were surrounded by fire and that auroras were the light from those fires, reflected in the sky. One other possibility was that the sun threw its beams high in the sky although the sun it self was located beneath the edge of the earth plate. A third possibility was that glaciers could absorb so much power that they began to shine.

One of the ancient Swedish names for aurora is sillblixt (herring flash). The name comes from people who thought that the aurora was a reflection of large herring shoals in the ocean. This is preserved in documents from Närke and different parts of Norway.

The natives, for example Indians and Lapplanders, that lives in the aurora zones today think that the aurora is something to be respected. This opinion is still active in our century. A lot of elderly people living in the north of Sweden can remember as children being told to act nice and silent when there were auroras in the sky. To misbehave at that time was very serious.

For the Lapplanders, as for other people in northern Europe, Asia and America the aurora was a place for the dead. Above all it was people who had died a violent or too early death who came to live in the aurora. It could be people who were murdered, killed in war, took their own life, died in child birth or unborn children.

The Lapplanders thought that auroras and the weather were connected. When the aurora was flaming high in the sky the weather should be warm. By magic influence of the aurora they thought it was possible to also influence the weather. This could be done in many different ways. In Kvikkjokk they called out a chant which started "gokseth (aurora) lipi, lipi". Lipi is short for lihphuit that means flutter. From Vilhelmina it is told that you could make the aurora flutter by waving a white sheet.

All people did not think that a fluttering aurora ment warm weather, some thought that it was getting cold others that there was a storm comming. Most people did belive that a fluttering aurora ment changes in the weather though.

Why are there auroras?
The Earth is surrounded by a thin gas cover, the atmosphere, and in the space above fast charged particles, plasma, are moving. Auroras arise when some of those particles enter the Earth's atmosphere and collide with atoms and molecules. When the particles collide the energy used to give them their velocity changes into a light, the aurora.

The particles that make auroras come from the ionosphere but have got an extremely high velocity due to the energy from the solar wind.The particles are caught by the Earth's magnetic field and are steered towards the poles. When a particle reaches the atmosphere it collides with one of the many present atoms.

When the particle collides with an atom the atom takes over some of the energy thet has given the particle its velocity. The particle keeps on moving but with less velocity, since it has lost some energy to the atom. The particle soon collides with a different atom.

The atom that has taken over some energy from the particle has now got too much energy and lets go of it. The surplus energy becomes light. The next atom that collides with the particle also takes over some of its kinetic energy, resulting in the particle losing even more velocity. The new atom also lets go of the energy. As the particle moves down through the atmosphere the atoms become more and more crowded, resulting in more collisions for the particle. Each time the particle collides it moves a bit slower and more light is emitted.

When the particle has collided a number of times it has lost so much of its kinetic energy that it stops moving. This occurs when the particle is approximately 100 kilometres from the Earth's surface. When a lot of particles collide with atoms, releasing light, an aurora occurs.

For auroras to arise on a planet five things are required. First of all the planet has to have an atmosphere. The atmosphere is the screen upon which the aurora is shown. If there was no atmosphere the particles from space would find no atoms to collide with and no light would be visible.

Second, there must be charged particles, plasma, that can collide with the atmosphere. If there were no particles the situation would be the same as above.

Third, something that can steer the plasma particles down to the atmosphere is needed. That is a magnetic field. If the magnetic field was not present most of the particles would miss the earth and keep moving through space. Fourth, an energy source that can give the plasma particles all the energy they need to create auroras is required. On Earth that energy source is the Sun. If the particles were not provided with all the necessary energy auroras would not occur.

Lastly, something to carry the energy from the Sun to the particles is needed. This is the solar wind.

Tips for studying auroras

  • It has to be dark and fairly calm weather.

  • It is very important to look often. The most intense part of an aurora often lasts only between 10- 30 minutes.

  • It can sometimes be hard to see the difference between a faint aurora and a cloud. If it is an aurora you can see stars through it. Auroras are often greenish and change shape in a different way than a cloud.

  • In Scandinavia the most active auroras are often seen before midnight. The aurora can be photographed by an ordinary camera, but a fast film is recommended (for example 400 ASA).

 

The text is an abstract from the book by Ingrid
Sandahl, Norrsken - budbärare från rymden
(Stockholm: Atlantis, 1998).
A more complete version is found on http://quasar.irf.se/norrsken/Norrsken_mainpage.html

   
     
You can see the northern lights in Lainio in Swedish Lapland
Request more information or make a reservation

 

Lainio Vildmark • Lainio by, SE-980 10 • Vittangi • Tel +46 (0)981-410 25 • Fax +46 (0)981-400 00 • E-post: info@lainio.com