Aurora Borealis - Northern Lights

Virtual Finland: "My earliest recollection of the Aurora Borealis, the Northern Lights, is from a song of the 1950s called 'the Northern Lights of Old Aberdeen', which I always took to be a reference not to Scottish traffic arrangements but to the celestial phenomenon of bands, curtains or streamers of coloured light that appear in the sky predominantly in the Arctic and Antarctic regions of the earth. In the Antarctic, the lights are called the Aurora Australis, or Southern Lights. They are visible, though less frequently, also outside those zones. I do not know how often the Northern Lights appear in northern Scotland but in the far north of this country, in Finnish Lapland, the number of auroral displays can be as high as 200 a year. In southern Finland the number is usually fewer than 20.

The sun gives off high-energy charged particles (also called ions) that travel out into space at speeds of 300 to 1200 kilometres per second. A cloud of such particles is called a plasma. The stream of plasma coming from the sun is known as the solar wind. As the solar wind interacts with the edge of the earth's magnetic field, some of the particles are trapped by it and they follow the lines of magnetic force down into the ionosphere, the section of the earth's atmosphere that extends from about 60 to 600 kilometres above the earth's surface. When the particles collide with the gases in the ionosphere they start to glow, producing the spectacle that we know as the auroras, northern and southern. The array of colours consists of red, green, blue and violet.

The Northern Lights are constantly in motion because of the changing interaction between the solar wind and the earth's magnetic field. The solar wind commonly generates up to 1000,000 megawatts of electricity in an auroral display and this can cause interference with power lines, radio and television broadcasts and satellite communications. By studying the auroras, scientists can learn more about the solar wind, how it affects the earth's atmosphere and how the energy of the auroras might be exploited for useful purposes. "