Snowflakes: Winter's Magic
February 06, 2012
Many of us dread the cold winter months, but beauty can be found even in this season. The icicles that form on the edges of your roof look like crystal stalactites. The term winter wonderland can be an accurate description of a snowy landscape with the bright sun reflecting off the pure white surfaces. What is a snowflake? How do snowflakes form? Inquiring minds want to know. Here are a few facts that I found on this subject:
- Snowflakes and snow crystals are made of ice, and pretty much nothing more. A snow crystal, as the name implies, is a single crystal of ice. A snowflake is a more general term; it can mean an individual snow crystal, or a few snow crystals stuck together, or large agglomerations of snow crystals that form "puff-balls" that float down from the clouds.
- Snowflakes are not frozen raindrops. Sometimes raindrops do freeze as they fall, but this is called sleet. Sleet particles don't have any of the elaborate and symmetrical patterning found in snow crystals. Snow crystals form when water vapor condenses directly into ice, which happens in the clouds. The patterns emerge as the crystals grow.
- When snow crystals are very small, they are mostly in the form of simple hexagonal prisms. But as they grow, branches sprout from the corners to make more complex shapes.
Here is a good question: Why is snow white? No, it's not a white dye. Snow is made of ice crystals, and up close the individual crystals look clear, like glass. A large pile of snow crystals looks white for the same reason a pile of crushed glass looks white. Incident light is partially reflected by an ice surface, again just as it is from a glass surface. When you have a lot of partially reflecting surfaces, which you do in a snow bank, then incident light bounces around and eventually scatters back out. Since all colors are scattered roughly equally well, the snow bank appears white. In fact, the ice does absorbs some light while it's bouncing around, and red light is absorbed more readily than blue light. Thus, if you look inside a snow bank you can sometimes see a blue color.
Some great books on this subject that can be found at your local library are The Secret Life of a Snowflake by Kenneth George Libbrecht found in adult nonfiction and The Snowflake: Winter's Secret Beauty located in juvenile nonfiction by Kenneth George Libbrecht.