|MadSci Network: Astronomy|
The former position is correct; the Aurora Borealis( and Australis) is due to an influx of charged particles from the Sun into our magnetosphere. This flux of charged particles is increased by solar activity such as solar flares. Perhaps one of the nicest recent examples was the magnificent aurora of March 1989, seen in such comparatively southern latitudes as most of England and some US middle latitude states. Two days before this there was a massive solar flare, embedded within a large and complex group of sunspots ( I saw and drew these through my regular solar observing programme for the British Astronomical Association's solar section. Number, size and complexity of sunspots vary, as you know, in an approximately 11 year cycle, and the emission of charged particles from flares, the cause of aurorae, is directly related to solar activity as shown by the sunspot cycle. Solar flares and aurorae can of course occur outside maxima sporadically but the probability and intensity of these events is tied to the cycle as described. By contrast, during the "Maunder Minimum" period(1645-1715AD) in which virtually no sunspot activity was detected for 70 years, there was also a complete absence of recorded aurorae over a 37 year period ( J.Eddy, High Altitude Observatory Reference). The Restless Sun, by Donat Wentzel , Smithsonian Library of the Solar System,1989 -- Michael Martin-Smith
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