Happy Snow Day! A look at a snowflake’s six sides

Here’s a look at a snowflake’s six sides from Bill Marvel at The Dallas Morning News and McClatchy Tribune.  

By Bill Marvel, The Dallas Morning News

Next time it snows, take a minute from sledding or skating or snowball fights to look closely at snowflakes. A dark piece of cloth, such as a wool mitten,and a magnifying glass will help.

Almost all snowflakes look like stars with six points,or flowers with six petals. But why six? Why not eight or five or for that matter, 20?

Four hundred years ago, a scientist named Johannes Kepler thought he knew the answer, and he wrote to a friend about it. Each snowflake, Kepler wrote, starts with a round droplet of frozen water. So far, so good. If you arrange pennies on a table and pack them as closely as possible, you will find that each penny touches exactly six other pennies. No more, no less. Thus, Kepler said,if you pack round droplets of ice closely together, each will be surrounded by exactly six other round droplets.

In the same way, he announced,each snowflake begins with a six-sided cluster of ice droplets,and it grows from there. Sort of like a bee honeycomb. Good guess, but Kepler was wrong.

Scientists discovered the real reason several centuries later. Snowflakes are six-sided because of the way atoms stick together. Each molecule of water is made up of one big oxygen atom and two little hydrogen atoms. Think of two little cherries stuck to a big apple, like ears.

The hydrogen atoms will stick to the oxygen atom, but they will not stick to another hydrogen atom.

As the temperature falls below freezing, water molecules in the air start sticking to one another, forming ice. Like people shaking hands, each oxygen atom grabs one of the hydrogen atoms of another molecule.That molecule, in turn,grabs the hydrogen atom of yet another molecule,until six of the molecules link together in a tiny six-sided crystal called a hexagon.

As that ice crystal falls through the air,it bumps against other molecules of water that stick to the corners of the hexagon and freeze. Pretty soon, the original crystal starts to grow six long arms. Meanwhile, the arms start to grow branches. Repeat the process often enough — say,about 10,000,000,000,000,000,000,000,000 times —and you get a snowflake just big enough to see.You could look at snowflakes all day during the thickest blizzard and never find two that perfectly match. You could look for the rest of your life ,in fact. That’s because, like people,each snowflake encounters different conditions as it goes through life — different air currents, different temperatures,different moisture — and so it forms differently. Like people, no two snowflakes are exactly alike.

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