The formation of snowflakes—essentially, the idiosyncratic way that water crystallizes when suspended in our atmosphere—is an extremely complex process that still hasn't been fully described by scientific formulas. "People think that a snowflake is just a frozen raindrop," says Caltech physics professor Kenneth Libbrecht, who's spent the past few decades studying the process of snowflake formation. "But that's sleet, just little ice cubes, and not even close to what a snowflake is."