A Terrela is a small sphere simulated the earth with his magnetic field. The first Terrela was made one century ago by K. Birkeland in Norway.

The Terrela explain the special shape of the polar lights (aurorae). It also proves than the polar lights are linked with the sun and in particularly the solar wind.
The solar wind is a flood of electric particles. It is essentially made of protons; they travel from the Sun with a speed of approximately 400km/h. When the wind arrives near the earth it kicks the earth magnetic field. The particles are drove inside the earth magnetic field and fall in the atmosphere in the polar areas. The contact of the particles and the atoms of the atmosphere create a typical light called the northern light. At the earth size the northern lights have a circular shape.
The Terrela is a small sphere of copper. A strong magnet is set inside the sphere. The sphere is lay inside a vacuum chamber. The low pressure is the same than the atmosphere at 100km high (where the northern light appears). The sphere is linked at an electrical power supply (between 0-1000V DC) on the positive plug. A flat electrode inside the chamber is linked with the negative electric plug. It creates the solar wind.
The result is very impressive. We can see moving lights created by the transfer of energy between the electrical particles and the small quantity of nitrogen inside the vacuum chamber. We can also see the aurora oval, the same shape than the real polar lights.
We made this experiment with a team of 7 pupils. Age 15-18. The research and the building took 1 year.
Thanks to Jean Lilensten, scientist in the LPG.

Polar light in Tromso (nov 1995)	Polar light in Tromso (nov 1995)
The shape of the polar light for the space (NASA)	Birkeland and his experiment.
Our Terrela	A detail of the discharge on our Terrela
The map of our experiment	A 3D simulation of our experiment.