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Sun Dogs

  1. What are Sundogs?
  2. How are sundogs formed?
  3. When and where is it best to see sundogs?
     Written by: John K.W. Chan


  1. What are Sundogs?

     

    Sundogs are bright areas on either side of the sun usually superimposed onto an ice halo.  Sundogs are also known as mock suns but they are more properly called parhelia.


    Sun Dogs 1
    An ice halo with a sundog at the Amundsen-Scott South Pole Station. Courtesy of John K.W. Chan

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  2. How are sundogs formed?

     

    Sundogs are formed when sunlight is refracted by 22 degrees through the flat plates of hexagonal ice crystals.  The observer then sees two apparent images of the sun approximately 22 degrees on either side.


    diagram2


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  3. When and where is it best to see sundogs?

     

    Sundogs can be seen when the sun is close to the horizon and the air is filled with ice crystals or when cirrus clouds are present in the sky.  They are occasionally observed in places that are permanently covered in snow or ice, such as the Artic, Antarctic, and high mountainous regions.


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Last revision date: <20 Dec 2012>