OneAndOneIs2

So.. when snow's on the ground, have you ever noticed how all the things that you usually think are nice and clean and white suddenly look drab and yellowish and dirty?

Have you ever wondered why snow is such a pure white?

Especially when the blanket of snow on the ground is made of ice, water, and air - all of which are clear.

In fact, the same thing happens with other stuff too. Take an egg white, whisk it, and even though it's clear egg and clear air, it's white foam. Fog is white, but it's water and air.

It's called a colloid - a mixture of two substances that don't mix.

(Not an oxymoron: Oil and water famously don't mix. But emulsions like milk and mayonnaise are a mix of those two things.)

Anyway. Snow isn't made up of things that are white, it's made up of things that are clear: Water and air. And as you'll know from looking at a glass of water, light bends when it goes from water to air, and vice versa.

So what happens when you have thousands and thousands of instances of light passing through water (snowflakes) and air (the space between flakes)?

It gets bent all over the damn place, that's what. It gets scattered everywhere, and a surface that scatters light without absorbing any of it, of course, appears white.

Air and water *do* absorb light to some extent, of course, but not enough to notice in a few inches of snow.

So snow isn't white because it's white. It's white because it's completely clear and just scatters the light so that it *looks* white.

This, incidentally, is also what polar bears do. Polar bears are black, and their fur is transparent. This means that they absorb heat from sunlight as much as possible, as it shines through their clear coats, but lose the minimum of their body heat due to radiation as their coats scatter it back towards them.

Clever, eh?