Why is snow white?
No, it’s not a white dye. Snow is made of ice crystals, and up close the individual crystals look clear, like glass. A large pile of snow crystals looks white for the same reason a pile of crushed glass looks white. Incident light is partially reflected by an ice surface, again just as it is from a glass surface. When you have a lot of partially reflecting surfaces, which you do in a snow bank, then incident light bounces around and eventually scatters back out. Since all colors are scattered roughly equally well, the snow bank appears white. In fact, the ice does absorbs some light while it’s bouncing around, and red light is absorbed more readily than blue light. Thus, if you look inside a snow bank you can sometimes see a blue color. I took a few pictures of this once in the California mountains.
Visible sunlight is white. Most natural materials absorb some sunlight which gives them their color. Snow, however, reflects most of the sunlight. The complex structure of snow crystals results in countless tiny surfaces from which visible light is efficiently reflected. What little sunlight is absorbed by snow is absorbed uniformly over the wavelengths of visible light thus giving snow its white appearance.
Light does not penetrate into snow very far before being scattered back to the viewer. However, the next time you are in an igloo, notice that it is blue inside. You can also poke a stick into some snow, shade the area around the hole, and look deep into the snowpack. The light that has traveled some distance through the snow will be enhanced in blue.
One of the reasons that so many people love snow is that it coats everything in a clean, “pure” white blanket. We even talk about snow in these terms — weatherman say that we’ll be getting “some of the white stuff” and every December you’re likely to hear the song “White Christmas” over and over again. Snow wouldn’t be snow if it wasn’t white. But if you think about it, it seems weird that snow is white at all, since it’s just a bunch of ice crystals stuck together. So where does it get its distinctive color? To understand where the whiteness comes from, we need to back up and look at why different things have different colors in the first place. Visible light is made up of many different frequencies of light. Our eyes detect different frequencies as different colors. Different objects have different
