Why Snow Is White


Science Explains the Color of Ice and Snow

Snow appears white because the faceted snowflakes reflect light.  (Stephane Mignon)

Snow appears white because the faceted snowflakes reflect light. (Stephane Mignon)

Snowflakes are crystals of frozen water. Water and ice appear clear or slightly blue in large volumes, so why is snow white? The reason has to do with the way light interacts with snowflakes and the air molecules packed between each and every snowflake.

Let’s start with how light interacts with snow. Water, ice, and an individual snowflake may appear transparent or clear, but water actually is translucent. The difference is that light can pass through a transparent material unchanged, while it is bent when passing through a translucent material. Light hits a snowflake and is bent and scattered across the spectrum by the facets and imperfections in each crystal. The scattering results in white light, in the same way a pile of sugar or salt appears white even though each individual crystal appears clear.

Blue Snow

Snowflakes scatter all frequencies of visible light, so the net effect is to produce white light, but deep layers of snow or compacted snow may appear blue. There is little air between crystals in compacted snow or ice, so there is less opportunity for light to be reflected. Thick layers absorb enough red light to cause this snow to appear blue. Snow also can appear blue if it has a layer of ice, which can reflect back the blue of the sky.

 

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