Here's how it works: A snowflake starts out as a simple hexagonal prism. As each flake falls, it bumps into a unique range of shape-changing conditions.
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In the 1970s, researchers at the Science University of Tokyo discovered that humidity, temperature, and air pressure determine the shape of a snowflake.
“Although no two crystals end up exactly alike, the six arms of a single crystal all travel together, so they all grow in synchrony, giving each falling crystal a unique and intricate structure with a recognizable symmetry,” said Kenneth Libbrecht, a physicist at the California Institute of Technology.