MadSci Network: Astronomy

Re: Is the Aurora more or less active when the sun is active?-See below

Date: Mon Nov 15 16:55:21 1999
Posted By: Michael Martin-Smith, Other (pls. specify below), Family Physician, Fellow,BIS, amateur astronomer( BAA), British Interplanetary Society
Area of science: Astronomy
ID: 942617610.As

   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 

Michael Martin-Smith

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