What a snowflake's shape says about where it's been
To take a photo of a single ice crystal, you need a photographic microscope. But examining snowflakes for yourself is easy. Just put a sheet of black construction paper on a cookie sheet in the freezer and wait for snow. During a snowfall, take the cookie sheet and a magnifying glass outside. Because the sheet is frozen, snowflakes falling on the cookie sheet will last longer.
You'll likely see a wide variety of shapes, including the six-pointed "stars" that most people imagine when they think of snowflakes. But snowflakes come in many shapes. The shapes depend on what the temperature was where they formed.
If you see thin, hexagonal (six-sided) platelike flakes, that means they formed in air that was 32 to 25 degrees F. In colder air (25 to 21 degrees F.), needle shapes occur. Long, hollow hexagonal columns appear from 21 to 14 degrees F.
Flowerlike "sector plates" form at 14 to 10 degrees F. Finally, six-pointed stars (called dendrites) appear from 10 to 3 degrees F. Sector-plate flakes reappear at minus 3 to minus 8 degrees F. Shorter hollow columns form at minus 8 degrees F. and colder. You may also see combinations of these shapes, as snowflakes may fall through different temperature layers as they form.
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