Snowflakes — Secrets of unusual forms of ice crystals

December 20, 2011 4:06

These luxurious snowflakes appear at minus 15 degrees.  Photo: From the collection of physics Kenneth Librehta.

These luxurious snowflakes appear at minus 15 degrees. Photo: From the collection of physics Kenneth Librehta.

In snowflakes order and chaos coexist.
Secrets of unusual forms ice crystals reveal the physics.


It turns out, the snowflake has weight. Usually weighs about 1 milligram. "Choice" — about 3 milligrams. Such heavy flakes like saucers circling up to 10 centimeters in diameter, fell out, for example, in Moscow on 30 April 1944. A very huge snowflake was recorded in 1887 in the U.S. state of Montana. Its diameter is 38 cm and thickness — 20 cm

Billions of these same "weightless" natural crystals influence even the rotation of the Earth: a little slow. Only in the summer months, when the snow is covered only 9 percent of the planet's surface, snow weighs 7.4 trillion tons. By the end of winter in the Northern Hemisphere snow mass is 13 500 000 000 000 tons. It is assumed that in a cubic meter of snow is 350 million snowflakes, each one is unique.

— Structure and appearance of ice crystals depends on where they fall, — the world's most famous explorer snowflakes — physics professor Kenneth Libbrecht (Kenneth Libbrecht) from the California Institute of Technology. — The most beautiful and complex structure snowflakes fall where the climate more severe — for example, in Alaska or Siberia. But in the big cities, where the climate is milder, the structure of snow crystals much easier. However, of assembly of these complex symmetric structures set — and still could not find two of them are alike.

Snowflakes under the microscope.  Photo: From the collection of physics Kenneth Librehta.

Snowflakes under the microscope. Photo: From the collection of physics Kenneth Librehta.

Professor Libbrecht grows snowflakes artificially in the laboratory and natural photographs. He developed a special camera with a built microscope to the "field" research. To the structure of snowflakes was clearly visible in the photo, the sample is illuminated in a special way, and she works as a complex snowflake lens. Photographing Snowflakes is necessary very quickly: when they descend from the sky, then stop growing and almost immediately begin to lose sharpness faces.

— There is no four-, five-and eight-sided snowflakes, — says the professor. — In general, they are strictly a hexagonal shape. From the point of view of crystallography, it is the most natural form of the crystal. Although there are three instances, and c, and with twelve sides.

But here's the paradox: all in the world for some reason often get triangular.

Libbrecht intrigued by the mystery. He decided to find out why the triangular snowflakes in nature more. He used a special "snow machine" — a chamber in which to control the growth of snowflakes. The results showed that the "triangle" — quite simply the most stable. No disturbance of the air flow, be it even a big storm, do not change its shape. Others have their beauty under the onslaught of natural disasters to lose, so they can catch rare.

And other forms of snowflakes — set. Thus, according to the classification of the International Commission on Snow and Ice — there are such! — All ice crystals are divided into groups: plates, needles, stars, urchins, columns, fluff, cufflinks, prisms, and irregular shapes.

— The most common shape snowflakes can be found when there is little snow and blowing a light breeze, and the weather being particularly cold — says Libbrecht. — The model of ice crystals temperature affects so. For example, at -2 ° C are obtained flat disks. At -5 ° C — needles. At -15 ° C — big beautiful flakes, which are often portrayed on Christmas cards. At temperatures below -30 ° C — crystals, similar to columns.

And there's another mystery inherent in the structure of a snowflake, which tries to solve the professor.

— In her order and chaos coexist together — says Libbrecht. — So, from physics we know that depending on the conditions for obtaining a solid body must be either in a crystalline (when the atoms are arranged) or amorphous (where the atoms form a random network) state. Snowflakes also have a crystal lattice, in which the oxygen atoms are arranged orderly, forming regular hexagons, and the hydrogen atoms are arranged randomly. It was only later, in some magical way, these atoms are shuffled so that one obtains the real works of art.

And these masterpieces of nature is a decent place. In the town of Kaga on the island of Honshu (Japan) created the world's only museum of snowflakes. And Professor Libbrecht unique collection of rarities of snow that can be seen on his website


The legend about the first snow

The rebels at the time of the fall of the angels lost their white wings that covered the land of brilliant white carpet. So there was snow, and there was the first winter.


Bacteria cause snowfall?

A group of researchers from Louisiana State University (USA) have discovered: the rainfall is not only physical but also biological reasons. Specifically, blame bacteria that use snowflakes or raindrops as transportation — to get home. This is — in addition to the microorganisms become centers of condensation and crystallization, acting like dry ice, which is sprayed into the clouds, causing rain.

— Evaporation and wind carries the bacteria into the atmosphere, — professor Brent Kristner. — But to be there for a long time they can not. And create their own conditions for the return to earth. Bacteria Pseudomonas syringae, for example, secrete proteins that create structures similar to the crystal lattice of ice. Ice forms on them, even at zero temperature. From this form snowflakes. With the warmer weather — rain.

Svetlana KUZINA

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