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Looks Like Snow

For many of us stuck in the midst of a frozen winter, snow has become a four-letter word bordering on profanity. The white stuff falls from the skies, accumulating on roofs, sidewalks, car windshields and the cold earth. We shovel, sweep, brush, scrape, blow and plow it. We often curse it, but occasionally we revel in its beauty as it falls, spreading an insulating quiet across the land.

Snow is made up of flakes with a remarkable diversity in crystalline shapes. While the claim that no two snowflakes are the same may be true, their vast numbers make it highly unlikely that anyone would look to scientifically test this hypothesis. In a typical 10-inch snowfall one can expect upwards of a million snowflakes in a 2-square-foot area. While the breadth of snowflake variation may be astounding, they also have some equally amazing commonalities in structure. Perhaps by looking a little deeper into the snowflake we can persevere a little better through the remaining snows to fall.

Snowflakes have perplexed humans for some time. Over 2,000 years ago the Chinese scholar T’ang Chin used his knowledge of alchemy to proclaim, “Since six is the true number of water, when water congeals into flowers they must be six pointed.” The six-pointed flowers he refers to are snowflakes. T’ang Chin’s writings provide one of the earliest known references to the hexagonal shape fundamental to the formation of snowflakes.

References to the six-pointed structure of snowflakes would not appear in European texts until the 13th-century writings of the Scandinavian Albertus Magnus. Some four centuries later Western snowflake scholarship received a critical boost when the German astronomer Johannes Kepler wrote an essay in 1610 entitled “On the six-cornered snowflake.” In this discourse by the scientist best known for showing how planets revolve around the sun, Kepler reasoned that snowflake shape resulted from the way globules of water packed together. Later in the 17th century, the refinement of the microscope allowed English inventor, physicist and mathematician Robert Hooke to make detailed snowflake sketches. These drawings would confirm the importance to snowflakes of the number six, put forth by T’ang Chin on the other side of the planet nearly 2,000 years earlier.

It was not until the later half of the 18th century that European science began to establish the connection between air temperature and snowflake form. In 1762, a French snowflake freak by the name of M. Guettard hypothesized that temperature was the determining factor in flake shape. Guettard’s hypothesis would remain untested until the 1930s, when a Japanese researcher with the help of some rabbits finally put it to a test.

Ukichiro Nakaya, a researcher at Hokkaido University came up with an interesting approach to determining the effects of temperature on flake form. After setting up a room in which he could control the temperature down to 22 degrees below 0 Farenheit, Nakaya used the tips of rabbit hairs to grow artificial snowflakes. As he lowered the temperature, Nakaya found that the crystals of ice that formed on his rabbit hairs changed.

In the temperature range of 32 to 26.5 F Nakaya’s snowflakes were flat and platelike with hexagonal shapes. As the temperature dropped to between 26.5 and 23 F, the hexagonal crystals took on a more needlelike shape. Dropping below 23 F down to minus 13 degrees, his flakes took on the shape of stars with six points that displayed elaborate feathery branchings. From minus 13 degrees down to minus 22 F, Nakaya’s snowflakes took on the form of prism-shaped crystals. While he had shown temperature’s role in snowflake shape, Nakaya also noted humidity as another important factor. Later research would add wind and barometric pressure to the list of influences.

Snowflakes got their big American debut as an art form in 1931 when Vermont farmer Wilson Bentley published his book Snow Crystals. The book included about one third of the 6,000 photos of flakes he’d taken since the 1880s, often using nothing more than a box camera and simple microscope—coupled with a wealth of patience. Bentley’s photos brought to the public’s eye the variation, hexagonal structure and awesome beauty of the snowflake. So how do these beauties take shape?

Snowflakes form on particles in the atmosphere. A distinct hexagonal symmetry emerges in the process of flake formation as water molecules interlock with four other water molecules through their hydrogen bonds. As additional water molecules are attracted to the forming flake they attach to the corners of the hexagon and may lead to elaborate six-pointed star formations, though mystery still surrounds some of these dynamics.

According to Kenneth Libbrecht, chair of Cal Tech’s physics department and author of The Snowflake, Winter’s Secret Beauty, a typical snowflake is made up of a billion billion water molecules. Of these, about a thousand have come from each of us through exhalation and evaporation.

As they form and fall to earth, snowflakes attract from the atmosphere substances like potassium, sulphate, calcium and nitrates that make snow an important fertilizer, enriching soil as it melts. It also cleanses the air as it falls. Snow, like rain, also picks up pollutants like sulphur dioxide, resulting in acid snow, threatening the life of rivers and lakes.

If you’d like to get a better look at snowflakes before the winter’s gone, get a piece of dark material and attach it to a piece of cardboard. Take this and a magnifying glass outside and let them acclimate to the cold. Once everything is chilled down you can catch snowflakes on your material and check the little wonders out directly.

So as those flakes fall, check them out and remember just how amazing these frozen bits of water can be.

—Tom Nattell


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