Snowflakes

Why do snowflakes tend to have a six-sided symmetry? It relates back to the geometry of the humble water molecule.

"Snow forms when water vapor condenses into a crystal. Water molecules come in a 'V' shape, with an oxygen atom at the vertex and two hydrogen atoms forming the arms at an angle of about 104 degrees apart, close to the angle that the sides of a hexagon make with each other.

So when the first water molecules link up they naturally form what Dr. Libbrecht calls a 'puckered hexagon.' As more water molecules float by to join them, they build up a lattice of six-sided segments."