Why do snow crystals form in such complex and symmetrical shapes?
To see why snowflakes look like they do, consider the life history of a single snow crystal, as shown in the diagram at right. (Click on the picture for a larger view.) The story begins up in a cloud, when a minute cloud droplet first freezes into a tiny particle of ice. As water vapor starts condensing on its surface, the ice particle quickly develops facets, thus becoming a small hexagonal prism. For a while it keeps this simple faceted shape as it grows. As the crystal becomes larger, however, branches begin to sprout from the six corners of the hexagon (this is the third stage in the diagram at right). Since the atmospheric conditions (e. g. temperature and humidity) are nearly constant across the small crystal, the six budding arms all grow out at roughly the same rate. While it grows, the crystal is blown to and fro inside the clouds, so the temperature it sees changes randomly with time. But the crystal growth depends strongly on temperature (as is seen in the morphology diagram
