The answer comes from the fact that snow consists of
millions of tiny crystals of ice - snowflakes. Each
snowflake has many points and surfaces. So a snow
layer such as this scene consists of millions and millions
of tiny crystal faces of colorless ice. Each surface
of a clear crystal reflects part of the incident
light. This is called "specular reflection".
Specular reflection can be seen on a piece of clear ice in
the photo below. On the left end of the piece of
ice, the ice is clear, but a distant light is partially
reflected by the surface. The same partial reflection
enables us to use a clear window as a partial reflecting
mirror. The amount of partial reflection depends on
the index of refraction of the transparent material.
The interior of the ice piece is all "milky" due to the
myriads of tiny air bubbles in the ice. The many air
bubbles are tiny surfaces in the ice that partially reflect
the light in many directions - giving it a "milky"
appearance. In the snow, the specular reflection from
the millions and millions of tiny surfaces within the snow
eventually reflects virtually all the incident in random
directions Thus, even though the individual snow
crystals are colorless, the scattering of all the incident
light in all directions gives the snow the white color - the
same color as the source of the light impinging on it.
This photo commemorates the first major snowstorm in
Western North Carolina for several years.
Don't forget to get a Valentine for your sweetheart!
Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us. Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to firstname.lastname@example.org.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.