Chilling images out of Caltech

IT’S beginning to look a lot like Christmas -- or your winter holiday of choice -- for Caltech physics professor Ken Libbrecht: His photographs of snowflakes are featured on a new series of U.S. postage stamps.

“They just called me out of the blue,” Libbrecht said last week. Although the call came months ago, he couldn’t tell anyone because “for the longest time, I was sworn to secrecy.”

Actually, it’s not Libbrecht’s photographs but four images based on them that appear on the Holiday Snowflakes series. The stamps were scheduled to go on sale Friday. “I gave them a bunch of choices and they picked the four,” he said.

While his Caltech colleagues keep tabs on the San Andreas Fault and other such matters, Libbrecht, a native of snowy North Dakota, has spent about five years studying the physics of snowflake formation in hopes of gaining clues to crystal growth that may have wider application.

Besides, he says, ice is cheap and easy to produce: “We use snowflakes for the same reason we use fruit flies: They breed fast.”

The author of “Ken Libbrecht’s Field Guide to Snowflakes” says his website, www.snowcrystals.com, receives about 2 million hits annually.

He began his snowflake research in the lab, growing the crystals in refrigerated coolers and using precision micro-photography to capture the images.

Later, he devised a way of mounting a microscope in a suitcase, allowing him to take his photographic efforts into the field. The microscope is attached to a camera. “The most difficult part these days is getting this complex-looking instrument through airport security,” he said.

The key to photographing fallen snowflakes is speed, according to Libbrecht. Even in the cold, the sharper features quickly begin to degrade, leaving the flake looking lumpy instead of lacy.

The snowflakes used on the stamps were photographed in Fairbanks, Alaska; Michigan’s chilly Upper Peninsula; and Cochrane in Ontario, Canada.

Does the professor have favorites?

It’s the Ontario flakes, he said: “The temperatures are cold, but not too cold, and the weather brings light snow frequently.”

But the physicist also likes specimens from Fairbanks, which “sometimes offers some unusual crystal types because it is so cold.” He noted: “Warmer climates ... tend to produce less-spectacular crystals.”

And what of the widely held belief that no two snowflakes are alike?

“There’s a lot of them,” Libbrecht said enigmatically -- and revealed nothing more.

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Diane Haithman