The Geometry of Falling Ice

A snowflake is a single ice crystal falling through Earth's atmosphere. Clear ice appears white because facets scatter sunlight.

Each flake begins around a tiny particle called a nucleus. Clays, desert dust, and biological particles may be effective.

Ice crystals grow at the expense of water droplets via the Wegener–Bergeron–Findeisen process. Crystals reach hundreds of micrometers.

Wilson Alwyn Bentley photographed thousands of snowflakes with a microscope from 1885 onward. He really liked looking at ice.

Less than 0.1% of snowflakes are perfectly symmetrical.

Magono and Lee classified freshly formed snow crystals into 80 distinct shapes. Categories include needle, columnar, plate, and rimed crystals.

Freezing air down to -3 °C promotes planar crystals. Colder air down to -8 °C forms hollow columns or needles.

Guinness World Records lists aggregated snowflakes at Fort Keogh, Montana as 38 cm wide. They fell in January 1887.