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STEVE INSKEEP, host:

We'll report next on something that polar bears might like to see more often - snowflakes.

Ken Libbrecht is an astrophysicist and chair of the Physics Department at Caltech in Pasadena, California, and he studies snowflakes.

Dr. KEN LIBBRECHT (Chairman, Physics Department, Caltech; Astrophysicist): It's been said that snowflakes are like hieroglyphs from the sky. They sort of encode - in the shape of the crystal is encoded the conditions under which it grew.

INSKEEP: Libbrecht explores the physics of how snow crystals grow and form in the atmosphere.

Dr. LIBBRECHT: Everybody can kind of picture a snowflake in their head and yet very few people have thought about, you know, why they look like that — and very few scientists have really spent much time looking at that, either. And, in fact, we don't really understand the details of why they look like they do.

INSKEEP: Although we had plenty of time to wonder about it if you're in any part of the country that is having extremely cold whether today. Libbrecht photographed snow crystals as a hobby, and then he expanded with a Web site he called SnowCrystals.com. It became popular with, as he says, snowflake enthusiasts — science teachers and mathematicians who want to model snowflakes. Even the U.S. Postal Service, which turned one of his wintry images into a stamp.

Libbrecht travels to places like Vermont, Alaska, and Canada to understand how snowflakes get their shapes — for example, why they are symmetrical. And he breaks the science into fundamentals.

Dr. LIBBRECHT: A snow crystal forms up in the atmosphere, of course. It starts with, a small water droplet, which freezes into a very tiny piece of ice and then that grows and gets this hexagonal shape. Then, as it gets larger, these corners of the hexagon sprout branches and they can become very elaborate as it grows larger.

INSKEEP: If you want to know how he knows this, consider that he built his own microscope with a camera attached to take pictures. The whole thing fits in to a suitcase so he can take it along to any cold places.

The question he hears most often as he travels is whether, in fact, there are any two snowflakes that look alike.

Dr. LIBBRECHT: One thing you can do, as a physicist, is you can try to calculate how many ways there are to make a snowflake - and I've done that. And it's a very large number. The number of ways to make a complex snowflake is far greater than the total number of atoms in the universe. And with such large numbers, you can say fairly confidently that if you looked at all the snowflakes that grew on Earth, you would never see one that looked exactly the same.

INSKEEP: In other words, the answer is no. There are no two snowflakes that look alike. As with politicians no answer is straight, he says with scientists no answer is short.

To learn how to grow your own snow crystals and learn more about Ken Libbrecht's work just visit npr.org.

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