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Similar Snowflakes

February 24, 2011

A listener asks: Why do snowflakes appear so similar to each other?



Why are all snowflakes alike? I’m Bob Hirshon and this is Science Update.

We hear a lot about how every snowflake is unique, but Science Update listener Istvan Prazsac emailed us from Hungary, asking why snowflakes are so similar—each with exactly six sides. We asked Miriam Rossi, professor of chemistry at Vassar College. She says it all comes down to the way water molecules group together as they cool.

MIRIAM ROSSI (Vassar College):

Snowflakes are symetrical because they reflect the internal order of the water molecules as they arrange themselves in the solid state which is known as crystalization.


And the easiest way for them to bond is in groups of six. So you might wonder why every snowflake isn’t just a perfect hexagon. Rossi says that changes in temperature and humidity as the flake grows can result in a variety of patterns, giving us flakes that are all built on a hexagonal foundation, but with myriad forms. I’m Bob Hirshon for AAAS, the Science Society.