Caltech professor of physics Kenneth Libbrecht will tell you that this has to do with the ever-changing conditions in the clouds where snow crystals form. Now Libbrecht, widely known as the snowflake guru, has shed some light on a grand puzzle in snowflake science: why the canonical, six-armed “stellar” snowflakes wind up so thin and flat.
Laboratory-grown snowflakes provide new insights into the molecular dynamics of crystal growth. Here, high voltage was used to create thin ice needles, and stellar snowflakes subsequently grew on the ends of the needles.
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