Do You Know Why We See Snow as White?

A savant's story reveals the complexity of snowflakes and the simplicity of snow.

Mark Watson/Getty Images
Outside it is cold, cold. Ten degrees below, give or take. I step out with my coat zipped up to my chin and my feet encased in heavy rubber boots. The glittering street is empty; the wool-gray sky is low. Under my scarf and gloves and thermals I can feel my pulse begin to make a racket. I do not care. I wait.

A week before, the trees’ bare branches stood clean against blue sky. Now the sight of falling snowflakes makes me shiver; it fills the space in my head that is devoted to wonder. How beautiful they are, I think. When will they stop? In an hour? A day? A month?

The neighbors, who’ve lived in Ottawa far longer than I, tell me they have not seen this snowfall’s like in a generation. Shovels in hand, they dig paths from their garage doors out to the road. The older men affect expressions of both nonchalance and annoyance, but soon faint smiles form at the corners of their wind-chapped mouths.

Granted, it is exhausting to trudge to the shops. Every step seems to take an age. Hot under my onion layers of clothing, I carry a shirtful of perspiration back into the house. Wet socks unpeel like plasters from my feet; the warm air smarts my skin. Later, around a table, in the dusk of a candlelit supper, my friends and I exchange recollections of winters past. We talk sleds and toboggans and fierce snowball fights. I recall a childhood memory from London: the first time I heard the sound of falling snow.

“What did it sound like?” the evening’s host asks me.

“It sounded like someone slowly rubbing his hands together.”

Yes, my friends say, laughing. Yes, we can hear what you mean.

One man laughs louder than the others. I do not catch his name; he is not a regular guest. I gather he is some kind of scientist.

“Do you know why we see snow as white?” he asks. “It is all to do with how the sides of the snowflakes reflect light.” All the colors in the spectrum, he explains to us, scatter out from the snow in roughly equal proportions, which we perceive as whiteness.

Now our host’s wife has a question. “Could the colors never come out in a different proportion?”

“Sometimes, if the snow is very deep,” he answers. In which case, the light that comes back to us can appear tinged with blue. “And sometimes a snowflake’s structure will resemble that of a diamond,” he continues. Light entering these flakes becomes so mangled as to dispense a rainbow of multicolored sparkles.

“Is it true that no two snowflakes are alike?” This question comes from the host’s teenage daughter.

It is true. Every snowflake has a basic six-sided structure, he says, but its spiraling descent sculpts each in a unique way: The minutest variations in air temperature or moisture make all the difference.

Still, researchers classify snowflakes by size, shape, and symmetry. For example, some snowflakes are flat and have broad arms, resembling stars, so that meteorologists speak of stellar plates, while those with deep ridges are called sectored plates. Branchy flakes, like those in Christmas decorations, go by the term stellar dendrites—from the Greek word for tree.

Sometimes snowflakes fall as columns of ice, which are called needles. Some, like conjoined twins, show 12 sides instead of the usual six, while others resemble bullets. Other possible shapes include the cup, the sheath, and arrowhead twins.

We listen wordlessly to the scientist’s explanations. Our rapt attention flatters him. His white hands, as he speaks, draw the shape of every snowflake in the air.

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