clock menu more-arrow no yes

Filed under:

Science of snow

This is how it begins: High in the clouds, when temperature conditions are just right, a tiny water droplet hooks up with a speck of dust. As the temperature around it continues to cool, the droplet begins to freeze, and as more water vapor condenses on its surface, a crystal begins to take shape. In a matter of minutes, fully formed ice crystals fall to the ground.

It's snowing.

Even though it is easy to take this process for granted, it is a pretty amazing one, says Kenneth Libbrecht, a professor of physics at the California Institute of Technology in Pasadena, who is known in some circles as Dr. Snow.

Remember the old Joni Mitchell song about clouds and their two sides? The same could be said for snow. If you tend to look at snow only as something to be dreaded, something that's cold and slick and dirty, then, as Mitchell would say, you don't know snow at all.

Libbrecht, on the other hand, knows snow. Libbrecht knows both the science and the beauty of snow. Libbrecht is deeply immersed in the magnificent, marvelous, mysterious world of snowflakes.

Snowflakes, he says, are not merely frozen raindrops. Nor are they formed from liquid water. Snowflakes come when ice condenses directly from water vapor in the air. It is a process that in many ways seems routine and normal, yet it is quite exceptional, says Libbrecht, and still not totally understood.

He has spent a lot of time researching the physics and mathematics of crystals and crystal formation, and he got into ice "because it's very easy to work with." It's easy to grow under controlled circumstances in the lab, it's inexpensive, and it doesn't have the safety concerns that many other crystal-forming substances do. "With ice, if you take off the lid, you can still breathe. If it spills, it just melts away," he said.

He got into snowflakes because they were fun, he said in a telephone chat from outside Montreal, where he had gone to find "better snow than we get in Southern California."

About 10 years ago, he said, he started reading about snow and its properties, "and I realized I hardly knew anything about it — even though I grew up in North Dakota, where we got plenty."

He read, he studied and, eventually, he began taking pictures of snowflakes "and that became my hobby."

Since then, there have been three books: "The Snowflake," "The Little Book of Snow," and his most recent, "Ken Libbrecht's Field Guide to Snowflakes," which came out this winter. They are all published by Voyageur Press.

His Web site — — showcases his pictures as well as provides information and background on everything from snow to how to take pictures of snowflakes.

This winter, four of his snowflake photos where chosen by the United States Postal Service for its Christmas stamp series. "Their call came out of the blue," said Libbrecht. "But it was pretty exciting. Some 1.5 billion stamps were sold."

The field guide came about, he said, because not very many people seem to be into snowflake watching. "It can't be the cold, because there are a lot of other popular winter activities. It can't be the equipment, since so very little is needed. It's certainly not the lack of beautiful snowflakes."

So, he decided, what was needed was a field guide. "I do a lot of bird-watching, too. It's almost as interesting as snowflake-watching. But you can't watch birds without a field guide to tell you what you're watching. Snowflake-watching is a lot easier, but I thought it would be fun to have a guide to let people know about the different types of snowflakes they can find."

To watch snowflakes, he said, all you need is an inexpensive little microscope that you can fold up and slip in your pocket. "Pull it out when it snows, and instead of brushing off the snow that lands on your sleeve, look at it."

Snowflakes come in myriad shapes. "No other substance grows in such a fascinating variety of crystalline forms as ice," Libbrecht said. "Snowflakes can grow into slender needles, thick columns, thin plates, multibranched stars or countless other intriguing shapes."

A lot of it has to do with temperature, wind, humidity levels and other factors. For example, thin, platelike crystals grow when the temperature is just below freezing, while slender columns and needles form when it is a few degrees colder. The large and most photogenic flakes form when the temperature is around 5 degrees F, and smaller plates and columns appear at lower temperatures.

Why and how temperature affects how the crystal grows is "still something of a scientific puzzle," said Libbrecht. The effect of temperature has been known since the 1930s, when the Japanese were doing a lot of research," he said, "but still, no one knows why."

Another thing you will quickly notice about snowflakes, he said, is that precise symmetry is rare. He goes through thousands of flakes to get the pictures he does. "Symmetry is inherent in snow crystals, but it is fragile and never perfect."

And that's one reason the standard adage that no two snowflakes are alike appears to hold up under intense scrutiny.

As snowflakes grow, they are subject to impacts of wind and temperature; as they fall, they can get jostled and broken, so there are differences.

That's not to say there aren't similarities, as well. Most snowflakes are six-sided. Rarely, you'll find some gorgeous 12-sided specimens. What you will never see are eight-sided snowflakes. That has to do with the basic structure of water molecules, he said.

The six-sided nature of snowflakes was recorded by German mathematician Johannes Kepler back in 1611. In 1665, Englishman Robert Hooke may have been the first to study snow through a microscope. In the 19th century, a man named Wilson A. Bentley was the first to take pictures of snowflakes. Despite this long history of research, "we still don't know how to solve all the equations," said Libbrecht.

Ice crystals are part of a larger field of study dealing with crystals and how they form and how they interact. Why is that good to know? "As a physicist, I'm not worried about applications," Libbrecht said. "I do the research for its own sake." But applications have come from crystal study. "My favorite example is with liquid crystals.That was big with chemists back in the '20s, who noticed weird optical properties. But no one said, this would make a good TV screen."

At CalTech, Libbrecht is head of the physics department and is also involved with the $400 million LIGO (Laser Interferometer Gravitational-Wave Observatory) project, which is looking at gravitational radiation, black holes and such. "But I'm a small player in that. Ice is my main thing."

Snowflake-watching can be a fun way to help you get through the winter, he said. The search for perfect flakes is exciting and challenging. "They don't come on demand, that's for sure. I enjoy the fact that whatever comes, it is always different. I never have the feeling that I've seen it before."