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| No two alike (probably): the amazing morphology of snowflakes. |
Unfortunately most of these linguistic riches are unprintable here.
You can catch it on your tongue. You can pack it into a ball and smash your best friend in the face. You can slide down hills of it on sticks or garbage can lids screaming or whooping or laughing. You can build a house out of it. You can lie and make angels in it.
You can simply walk in it, feeling the silence and the landscape getting soft and close.
But the next time it snows the first thing I'm going to do is grab my magnifying glass and run outside to look at car windshields, the better to appreciate the dance between destiny and contingency, the collision of law and chance that is one of nature's simplest but most sublime creations, the humble snowflake.
Blame it on "The Snowflake, Winter's Secret Beauty," a new book written by Dr. Kenneth Libbrecht, with photographs by Patricia Rasmussen. Dr. Libbrecht, chairman of the physics department at the California Institute of Technology, is a snowflake junkie who grew up in North Dakota, where the various forms of snow are plentiful this time of year. He grows snowflakes on needle tips in his lab when he is not busy looking for the gravity waves that, according to Einstein, should ripple the cosmos.
"A snowflake is a temporary work of art," Dr. Libbrecht writes in this book, which is part history, part physics lesson, part sumptuous photo gallery and overall field guide to the beauty so often lost afloat and underboot in this dark season.
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Pinned like transient butterflies in the gaze Dr. Libbrecht's special photo-microscope is an enormous shining variety, a sort of Benetton advertisement in ice.
Some look like stained glass, some like six-armed circuit boards inscribed with curious and purposeful-looking fine lines, some are spidery concoctions, but some seem almost bony, sturdy enough to tile a turtle's back, while others are embroidered six-armed crosses worthy of an illuminated manuscript or of heraldic insignia. Some are needles and some look like spiky mallets.
The flakes go by almost as many names as snow itself: dendrites, capped columns, needles, bullets, sectored plates, sheaths, split stars and chandelier crystals, not to mention diamond dust ? tiny crystals most often found suspended high in the coldest, driest parts of the atmosphere where they reflect and refract sunlight to create spectacles like halos, and spots of light called sundogs.
What they all have in common is a core of the six-pointed symmetry that adorns ski sweaters and Christmas tree ornaments. That symmetry has been the object of scholarly fascination since at least the time of Johannes Kepler, who adduced that it had something to do with as-yet-unknown physics.
We now know that classic shape is a consequence of basic atomic physics, Dr. Libbrecht explains.
snow forms when water vapor condenses into a crystal. Water molecules come in a "V" shape, with an oxygen atom at the vertex and two hydrogen atoms forming the arms at an angle of about 104 degrees apart, close to the angle that the sides of a hexagon make with each other.
So when the first water molecules link up they naturally form what Dr. Libbrecht calls a "puckered hexagon." As more water molecules float by to join them, they build up a lattice of six-sided segments.
But what happens next depends on such vagaries as the temperature and humidity in which this prototype snowflake finds itself, according to studies carried out by a Japanese nuclear physicist, Dr. Ukichiro Nakaya, at the University of Hokkaido, in the 1930's.
In relatively dry air, for example, the sides of the hexagon grow slowly and evenly into a plate or a six-sided rod. In more humid conditions, however, the corners of the hexagon begin to grow faster than the flat faces because water molecules in the surrounding air don't have to travel as far to land there.
The more the corners stick out, the more advantage they have attracting more molecules, and so the faster they grow. Corners become long branches; random bumps on the branches become side branches, resulting in the feathery shapes called dendrites.
Over the course of its life a snowflake may go through many different stages of growth as the wind dances it from cloud to cloud, from drier to moister or warmer or cooler environs, all of them leaving their marks on the final flake, as shown in Dr. Libbrecht's portrait gallery.
If snowflakes are art, he writes in the book, then wind is the artist.
By the time it is done growing there are about a billion billion water molecules in a typical snowflake, Dr. Libbrecht says. And on average, he calculates, each of us on Earth has contributed by exhalation and evaporation about 1,000 of the molecules in each snowflake.
It is this character-building growth experience that accounts for the vaunted individuality of snowflakes, the book explains.
The morphology of the snowflake that falls on your windshield depends on the random and erratic path it took from its birth as a seedling to get there. Since no two crystals will follow the exact same path, it is unlikely any two of them will look identical. "We can calculate the odds of identical snowflakes: they are astronomically small," Dr. Libbrecht said in an interview.Dr. Libbrecht said that when he was a boy building snow forts and throwing snowballs, he never dreamed that he would one day take a scientific interest in snow. In 1997, however, he became interested in the way crystals grew, and that led him to snowflakes. "Snowflakes are crystals," he said.
On a visit to his sister in North Dakota, he realized, like many a prodigal son, how much he had not appreciated as a child. They went out looking to see if they could find the different varieties of snowflake.
"They were all there," he said.
