What Are the Northern Lights and What Causes Them?
The Northern Lights are
long, waving streamers of light, often seen in the night sky in the Northern
Hemisphere during both warm and cold weather. These marvelous, wavering
illuminations are also called the Aurora Borealis, from the Latin words meaning
a “northern dawn”. They are most frequently seen between 65 degree and 80
degree northern latitude, but the area of visibility extends further south in
North America than in Europe.
The aurora of the southern hemisphere is called the Aurora Australis, from the Latin for “southern dawn”. The bands of light in the aurora seem to radiate from an arc and send their rays far across the heavens. They are most often white, but are sometimes green, red or yellowish. The luminous streamers may be almost straight, or they may wind backwards and forwards like glimmering snakes in the sky.
Sometimes the rays look like a fan, or form a crown round a dark centre. At other times the long beams of light may seem to fall downwards like the folds of a gigantic, shimmering curtain. Their apparent movement is often so rapid that they have been called the “Merry Dancers”.
Scientific studies of auroras began in 1716 with a spectacular display that was visible over the whole of Europe. The English astronomer Edmund Halley (1656-1742) proved a connection between them and the earth’s magnetism. But the exact cause of the auroras is still not completely understood.
The most likely theory is that they have their origin in streams of electrically charged particles from the sun, which are turned aside to the north and south magnetic poles on reaching the upper layers of the earth’s atmosphere. Auroras are most pronounced during magnetic storms, that is during the time that the earth’s magnetic field is most disturbed. They also tend to occur when there have been signs of unusual activity in the sun.