You’ve seen snow, but have you ever studied a snowflake? That is, have you looked hard at a falling crystal and seen its unique design up close?

It’s not easy to glimpse something so tiny that it often melts or blows away as soon as it lands. Imagine trying to photograph one!

But that’s what Ken Libbrecht has spent much of the past four years doing: catching snowflakes, putting them under a microscope and taking pictures. He loves doing it for the same reason he loves bird-watching: He gets to spend time in nature looking for something that’s hard to find.

“Snowflake-watching is just as much fun,” he said. “You can’t do it on a nice, warm, sunny day; but, hey, there are no mosquitoes.”

Libbrecht is a scientist who has written four books about snowflakes. You might even have seen some of his snowflake photos: Four are featured on U.S. postage stamps this holiday season.

Libbrecht didn’t do anything special to get his work turned into stamps – he was working in his lab one day when the U.S. Postal Service called. “It’s very exciting,” he said.

Libbrecht is interested in snowflakes because they are fairly complicated and because scientists don’t fully understand them. He goes on snowflake-hunting trips from his home in Southern California. Yes, there is snow in the mountains in California, but Libbrecht’s favorite hunting ground is in Canada, in northern Ontario.

His wife and two kids, now 14 and 17, usually go with him, but “this year I am going alone,” he said. “My family’s gotten kind of tired of it.”

In his latest book, “Ken Libbrecht’s Field Guide to Snowflakes,” he answers lots of questions about snowflakes in a way that’s easy to understand. Their beautiful crystal structure is mainly the result of two things: conditions in the sky and the structure of water molecules. A water molecule is the smallest unit that can be recognized as water.

A snowflake starts as a nearly invisible speck of dust. Tiny bits of water vapor (the gas form of water) attach to the dust, then freeze. These molecules are triangular, and as more of them attach to the dust they eventually create a hexagon, or six-sided shape.

Ken Libbrecht, of California, has spent four years chasing snowflakes, and he has written four books about the frozen water crystals.

Some snowflakes become flat hexagons and stay that way, sometimes with broad “petals” forming at the six corners, making them look like flowers. Other snowflakes turn into hexagonal columns.

But if the changes in temperature and humidity are just right, thin branches may sprout on a baby snowflake as it tumbles in the air, creating six-pointed starbursts called dendrites. These are usually the prettiest flakes and are most likely to form when the weather is either just below freezing (32 degrees Fahrenheit for water) or around 5 degrees. Brrrrr!

Perfect snowflake specimens – those lacelike flakes that Libbrecht loves – are hard to find, even when the weather seems ideal for creating them. “I’ve been in places where the temperature is 5 degrees and the wind is calm – and the snow still looks like sand,” he said.

Libbrecht has had some success growing snowflakes in his lab, but it’s not the same, he said. They’re not as pretty, and it’s a lot of work.

No, the best way to enjoy snowflakes is the old-fashioned way, he said: “You just go outside, and they fall from the sky by the billions.”

Become a snowflake watcher

1. A gentle snowfall is best.

2. Take a magnifying glass, sketch pad, pencil and a piece of black paper outside and wait a few minutes for the paper to get cold. (Black cloth will work, too.)

3. Hold the paper out flat until a few flakes land, then quickly examine them with the magnifying glass. Hunt for the best ones, or see how many types you can find. Sketch them quickly before they melt!

4. If you have a microscope, let some flakes fall on a slide and put it under the lens to see what you caught. No good hits? Dry the slide and try again.