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| Introduction |
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Many people living in the polar region, have stopped in their daily routine - even if it is bitterly cold, to watch the flaming diversity of lights fill the sky. The fluttering drapery of the aurora suggests dancing spirits and dynamic hordes to some.
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However, the physics behind the auroral problem is more complicated than the emission of lights. The light is the end product of many different physical processes in the solar system. Most important are charged particles from the Sun, magnetic fields in interplanetary space as well as on Earth, electric currents and the different gases in the atmosphere.
An auroral display clearly demonstrates that electromagnetic forces are important in our solar system. Northern light research is also important for learning about other celestial bodies. Norwegian researchers such as Birkeland, Størmer and Vegard were pioneers in the early history of auroral investigations. Even though our knowledge about auroras has increased considerably during the space age, we still do not know enough to predict the occurrence of auroras one week or even one day in advance. It is therefore important to continue auroral research, preferably with increasing levels of international cooperation. |
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| The northern lights over Scandinavia contain many different shapes and nearly all colours of the spectrum. |
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Auroral emissions carry messages from the source where they are generated. Because the intensity of auroras is weak compared with sunlight, there are limitations on the collection of auroral data. All ground measurements have to be carried out when the sky is clear and dark. Furthermore, you have to be far away from the Earth’s equator.
Auroras have clearly left their marks on our culture. They have been and still are an important source of inspiration for many artists. In the first part of the last century, the northern lights were considered to be very mysterious and so were often connected with superstition and mythology. Others considered the northern lights to be harbingers of war, plague and poverty.
Thus, in many countries the northern lights were seen as dangerous, especially for women. During the last 100 years, particularly in the space age, the mythology connected with auroras has practically disappeared – but this characteristic scenery of the polar sky is still an important source of inspiration for authors, painters and musicians. |
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What does the aurora look like? Northern light is a natural phenomenon that varies extensively in intensity, colour, dimension and shape. It is a dynamic display that can vary over orders of magnitude in seconds. Thus, the zone of maximum occurrence can change several hundred kilometres within minutes. Because of these enormous variations, it is exciting to watch and study. Most often, you see greenish or yellow-green ribbons stretching across the sky, roughly from east to west, usually with waves in them.
At the Andøya Rocket Range - or more general in northern Scandinavia, they would normally be near zenith. Further south those ribbons tend to be near the northern horizon. And if you look closely at them, you will note that they sometimes contain many parallel rays, running across their width (see picture above). The auroras may brighten or fade - a bit like flames in a fireplace, and just as mesmerizing. Some auroras are deep red, and these may be just a shapeless glow - or they may have rays, too. The direction of those rays is related – parallel, to the Earth’s magnetic field. The intensity of auroras can vary from a barely detectable glow to a light bright enough to completely veil the stars. The brightest colour in the aurora is green. Auroras are often brightest near the bottom. |
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