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Natural Snowflakes
  --Photo Gallery I
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  --Guide to Snowflakes
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  --Ice Crystal Halos
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Designer Snowflakes
  --I: First Attempts
  --II: Better Snowflakes
  --III: Precision Snow
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Frost Crystals
  --Guide to Frost
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Snowflake Physics
  --Snowflake Primer
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  --No Two Alike?
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Copyright Issues
Ice Crystal Halos
   ... Atmospheric displays arising from snow crystals ...

   When sunlight reflects and refracts off of tiny ice crystals in the atmosphere, the result can be ice crystal halos, which are related to rainbows (the latter being produced when sunlight reflects and refracts from water droplets). 

greenlerx.jpg (2521 bytes)tapex.jpg (2348 bytes)    The classic introduction to the physics of atmospheric light displays is Robert Greenler's Rainbows, Halos, and Glories. [1]  A more recent book focusing on halos is Atmospheric Halos, by Walter Tape [2].  The latter book describes ice crystal halos in roughly the same fashion as Greenler, but with emphasis on the exquisite halos that can be observed from the South Pole.  In addition to working with the best halo displays on the planet, Tape's photography is technically superb, resulting in spectacular images.

Halo7x.jpg (1091 bytes)   In Antarctica the temperatures are cold and the air is dry, so snow crystals grow very slowly.  This slow growth tends to produce very clean hexagonal prisms, which are well suited for producing beautiful atmospheric displays.  The example at left is a South Pole halo from Tape's book [2], showing a rich variety of arcs and halos. 

cartoonx.jpg (2575 bytes)kide_vr.jpg (6568 bytes)   Halos arise from the way minute ice crystals in the atmosphere scatter sunlight (or moonlight) into different angles.  The quality of a halo depends on the type and quality of the ice crystals that produce it.  A good web-based description to halo phenomena can be found at Atmospheric Halos.


[1] R. Greenler, Rainbows, Halos, and Glories (Cambridge University Press, 1980).
[2] W. Tape, Atmospheric Halos, Antarctic Research Series, Vol. 64, (American Geophysical Union, 1994).

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