Why is Snow White?

Yes! The burning (cooling?) question I know you've all been asking since you first set your eyes on the magical powdery stuff...why is snow white? It was on my way up to my geology summer job that I stumbled upon this thought. As I drove further north towards Armstrong Ontario (and then past it), I realized that there was snow on the sides of the road. But this wasn't December or even March. This was May! But anyway, it was then that I figured that I should find out why snow is white.

First, we should understand why things have colour in the first place. What we perceive as visible light is actually a combination of many different frequencies of light. Our eyes take in these differing frequencies and interpret them as colours. Where do these frequencies come from? Well, particles in objects vibrate in response to energy. Depending on the frequency of the energy, each object will have a vibration frequency which in turn determines the colour emitted. Also, the particles involved absorb a certain amount of light energy which is then absorbed as heat. As a consequence, certain objects can absorb certain frequencies of light more than others.

What happens next to the light frequencies that are not absorbed differs depending on the particles involved. In one case, the photons (light energy) emitted continue to pass through the particles of a material, resulting in a transparent object. In another case, the photons are re-emitted out of the material, so no light (or very little) passes through, resulting in an opaque object. The colour that we see is a combination of the light energy that the particles didn't absorb.

So now back to snow. We know that snow is just frozen water (ice) which is actually translucent. This leads us to conclude that the photons don't actually pass directly through the material, but actually change direction due to the particles of the material. This is due to interaction of the light photons with the molecular structure of the ice. This interaction alters the photon's path and it exits in a direction all together different than which it entered.

Since snow is just a group of individual ice crystals positioned together, the effect mentioned above occurs on a large scale. When light enters an ice crystal, its direction is altered and it goes through another ice crystal. This continues to happen until the light is bounced right out of the snow. Since it does this to every light frequency, all colours of light are shot back out. When all the colours of the visible spectrum are combined (which is what has occurred here with the ice crystals), we end up seeing the colour "white". Hence, snow! However, if we were to look at the individual ice crystals, we would see differing colours.

And there you have it! You now know why snow is white, and if you can connect the dots, why objects are the colours that they are.

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