Re: Why does the air sparkle when it's cold?

What you are seeing is something very familiar to anyone living in more 
northerly regions: ice crystals. When the temperatures drops to 
significantly below the freezing mark, moisture in the air doesn't 
precipitate out as fog, it goes directly to ice. In warmer temperatures, the 
crystals are hexagonal in shape, but when the temperatures drop to the -30 - 
-40 range, they often take on the form of ice needles. The latter form of 
ice crystal can produce some spectacular effects: pillars of light above the 
sun near sunrise or sunset, or bright spots or arcs of light offset 23 
degrees horizontally either side of the sun; what are affectionately known 
as "sun dogs". Checking your local library's collection of weather-related 
material will provide you with more detailed information on how these 
phenomema are produced, and under what conditions they occur.