Why does snow sometimes sparkle?

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Why does snow sometimes sparkle?
sparkling snow

Photo of snow in west Sierra Nevada by Itrovert

Sometimes on a sunny day, freshly fallen snow may appear to sparkle or glitter. This happens because when light hits an object light, it can be absorbed, in which case the object is heated; transmitted, in which case light passes through the object; or reflected, in which case it bounces back.

Clear water can transmit or reflect light (think of how a calm lake can reflect an image of the trees on the shoreline). Flat snowflakes resting on top of a blanket of snow also can act like a mirror, reflecting a portion of the sun’s image toward your eye. Each ‘sparkle’ is a reflection of the sun’s image from a single crystal. Whether we see the sparkle depends on the angle between the sun, the snowflake’s position on the snow and the location of our eye. When the angle is right, when we walk by a field of snow, we’ll see glitter as the sun is reflected by different snowflakes.

You may notice some faint colors in the sparkles. As light travels between air and water, the colors in the light separate, much as they do in a rainbow. The sun’s ray can reflect off different surfaces of the crystal. If the sunlight reflects off the back of the ice crystal, the colors may disperse as the light enters and exits the crystal, making those faint colors.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.