Reindeer Meets a Snowman

About this drawing

A reindeer and snowman would have a tough time without one bit of everyday science: snow. It starts high in a cloud, where water vapor freezes around a tiny speck of dust. That speck becomes a crystal of ice, which grows as it falls and picks up more vapor along the way.

Nearly every snowflake has six arms because of how water molecules fit together when they freeze, forming a hexagon. Temperature and humidity decide the rest. Depending on the conditions, a crystal can turn into a flat plate, a needle, or a branching star. Each one falls through its own path of changing air, so finding two exact matches is extremely unlikely.

Snow looks white even though ice is clear, since all those tiny crystal faces scatter light in every direction. It also traps plenty of air, so a deep layer acts like an insulating blanket for plants and small animals underneath. Anyone building a snowman learns another lesson fast. When the temperature hovers near freezing, each flake has a thin film of liquid water that glues it to its neighbors, which makes for perfect packing snow. On a truly bitter day, the snow stays dry and powdery, and it falls apart in your mittens no matter how hard you press.

• reindeer
• snowman
• snowflakes
• forest