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Today I learned about snow--particularly, snowflakes. Twice this winter it has snowed where the snow is extremely fluffy with huge flakes. You can actually see the little "snowflake" pattern in the snow, like you cut them out of paper. Last night I was informed that the shape of the snowflake is caused by the shape of water/ice itself (I was freezing and not paying much attention). So today I looked up Snow on Wikipedia and found out lots of interesting things about snow, some of which I didn't really understand because I don't know much about science.

In any case, the six-sided symmetry of a snowflake "arises from the hexagonal crystal structure of ordinary ice." Depending on how cold and how humid it is when the snowflake is forming, you'll get different shapes of snowflakes. The reason that each opposite arm is exactly symmetrical (well, not exactly, but close enough) isn't known for sure. It sounds like the most likely reason is just that the arms are forming at exactly the same time in exactly the same environment, so they end up looking alike.

There is a lot more information in the Wikipedia article if you're interested. There are also some REALLY cool pictures of snowflakes and snow crystals taken with an electron microscope. Check it out!