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January 4, 2010

All About Snowflakes

What are snowflakes?
Contrary to popular belief, snowflakes are not frozen raindrops (that is called sleet) even though they are composed almost entirely of ice. A snowflake is a broad term describing individual snow crystals or many snow crystals stuck together. The story of snowflakes goes back to the water cycle. As we all know, moisture evaporates into the air in the form of water vapor from bodies of water, plants, and animals. As air temperatures cool in the atmosphere, water vapor cools and condenses, forming clouds. Water vapor that cools to the point of freezing makes for snowy conditions.

Is it true that no two snowflakes are the same?
Yes, in fact, it is. That discovery is owed to a farmer named Wilson A. Bentley of Jericho, Vermont, who, in 1885, was the first person to photograph a snowflake. Over his lifetime Snowflake Bentley, as he became known, used photomicrography, or photography using a microscope, to record over 5,000 snowflakes.

Teacher Resource
There are a number of ways, from simple to sophisticated, for your class to collect and examine snowflakes.

Simple: Use a sheet of black construction paper to collect falling snowflakes during a storm and examine the flakes with a hand lens. Work quickly and do not expect to document the results very easily. This method works great for younger students and for those simply looking for the experience of seeing the form of a snowflake.

Sophisticated: Collect 1"x2" glass slides, larger pieces of scrap wood or other insulation material, and a clear plastic spray. In a cold place, place many slides upon the piece of wood and spray each slide with an even coating of plastic. Outside, collect snowflakes and leave the set-up in a cold ventilated or covered area for about 15 minutes until dry. The spray will replace the snow, leaving a permanent white plastic snowflake. Examine with a hand lens or microscope. Snowflakes are quite varied and yet individually unique. They can however be classified according to basic structure. The following chart is one of the many classification systems used for snowflakes:

Why the differences?

Air currents (which direction the air is moving)
Humidity (the amount of water vapor in the air)
How long it takes the crystal to fall
Wind speed
Amount of dust, salt, or other solid particles in the air
Pressure form the weight of other snow crystals
Combining shapes with other snow crystals

This article was originally printed in the Bioregional Outdoor Education Project's Fall 2009 newsletter.

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