According to Libbrecht’s calculations, enough snow forms in Earth’s atmosphere every 10 minutes to make a snowman for every living person on the planet. The vast majority, though, ends up melting before it ever hits the ground. But if the air is cold enough, snowflakes make it to the planet’s surface.
Libbrecht has traveled to places like Canada, Japan, and Sweden to study freshly fallen flakes firsthand. He catches them on a piece of foam as they drift down from the sky. Then he uses a paintbrush to carefully transfer the snowflakes to a glass slide. He quickly puts the slide under a microscope to examine each flake’s structure.
Snowflakes come in a wide variety of shapes. The most picturesque, says Libbrecht, are stellar dendrites, with their six branching arms. But snowflakes can also form prisms, needles, columns, and six-sided plates. By studying the size and shape of a snowflake, Libbrecht can determine the conditions under which it formed in the atmosphere (see Flake Formation). Temperature, for example, has the greatest effect on a snowflake’s shape. Humidity, or the amount of moisture in the air, affects how complex a snow crystal will be.