Why is snow white?

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Dear Tom,

I was wondering why snow is white?

Megan S.

Dear Megan,

As winter approaches, it’s time to revisit this frequently asked question. Visible sunlight consists of the full spectrum of wavelengths that are visible to us. Our brains interpret specific wavelengths within that spectrum as specific colors, but when all wavelengths are blended together we see white. Most materials absorb some of the sunlight that falls on them, but also reflect some of it, and it is the wavelength of the reflected light that reaches our eyes, that gives the material its color. Snow reflects nearly all of the sunlight that falls on it because the complex structure of snow crystals results in countless tiny surfaces that efficiently reflect light. The little sunlight that is absorbed by the snow is absorbed uniformly over the entire visible spectrum, thus giving snow its white appearance.

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