Kenneth Libbrecht is that rare person who, in the middle of winter, gleefully leaves Southern California for a place like Fairbanks, Alaska, where wintertime temperatures rarely rise above freezing.

Above: A hexagonal (six-sided) snow crystal, classified as a stellar dendrite. This crystal was photographed with an Olympus TG-6 camera after it landed on the sleeve of the authors fleece jacket.

MOLINE, Ill. — Snowflakes are frozen water crystals that can never be an exact replica of another. However, snowflakes can be classified into these broader types: dendrites, plates, columns, needles, ...