Aurora Borealis

The Aurora Borealis

The Sun is never calm. Narrow vertical gas-jets which begin on the bright surface and soar to as much as 10.000 kilometers into the chromosphere. They are always present and at any one time there may be as many as a quarter of a million of them.
The most dramatic are the flames, which usually occur above active spot-groups. They are short lived and generally last for few minutes. Few have been known to persist for few hours. The flares produce shockwaves in the corona and the chromosphere, and a mount of material is blown away from the Sun. The temperatures may rise to many millions of degrees. Radiations of all wavelenghts are particularly strong in the X - ray and ultraviolet regions of the electromagnetic spectrum.
The solar wind is made up of charged particles, which are made up of a mixture of electrons and the nuclei of atoms called ionized gas or plasma, sent out from the sun at all times. The ionized gas is also responsible for repelling the ion tails of comets, making them point away from the Sun. When these particles reach the Earth´s magnetic field, they are resposible for very beautiful  and magnificent displays of light in Earth´s atmosphere, called the polar lights or Aurora Borealis.
 As the solar wind passes the Earth, the average velocity of it is 300 to 400 kilometers per second. Astronomers are not sure how far it extends, and it is hoped that four spacecrafts, Pioneer 10 and 11, and Voyager 1 and 2, will keep on transmitting until they reach the edge of the heliosphere, the region where the solar wind ceases to be detectable.
The solar wind escapes through holes in the corona, where the magnetic field lines are open instead og looped.
The Earth´s atmosphere consist of 78% nitrogen and 21% oxygen, there is also argon, a little carbon dioxide and traces of krypton and xenon together with variable amount of water vapour. It is divided into layers. The lowest layer is called the troposphere and it expands upwards for about 8 km out to more than 17 kilometers. It is deepest over the equator and it is the layer where we can find clouds and the weather. Among these layers is one called ionosphere and that´s where the auroras occur, about 150 km high.

The auroras have been know for many centuries. For example the Roman emperor Tiberius who reigned from AD14 to 37, once dispatched his fireengines to the port of Ostia because a brilliant red aurora led him to believe that the whole town was on ablaze.

The auroras can be seen in various places such as Alaska, North Norway, North Sweden, Iceland and Finland. They can only be seen in countries near the polar regions and they are very common in Iceland. But they are rare in places like England in the south or from lower latitudes.

In the southern hemisphere the aurora borealis are simply called the Southern Lights.

Northern lights are often seen in an oval shaped zone around the magnetic pole. This is called the northern lights oval and it lies above the coastal areas of northern Norway over Alaska and Iceland.

The aurora occur only above altitudes of 80 kilometres and infrequently above 500 kilometres. The average altitude for normal intensity aurora is between 110 and 200 kilometres.

Aurora activity corresponds to sunspot activity, which follows an 11-year cycle.

Aurora Video

Northern Lights

UNDER CONSTRUCTION