Snow, Sky, and the Color Blue
by Becca Deysach
Broadcast 1.2004, 1.2016, and 1.5 & 1.8.2022
I am running downhill though wet snow on a hill above Lolo Pass, thinking to myself, “So this is what it feels like to be Sasquatch.” Only that giant creature has a body to match the size of his feet. Mine are strapped into a pair of big, red snowshoes, making me buoyant on the two feet of new snow. With each leap forward, I plant a ski pole into the cold whiteness, and nearly half of it is swallowed up. As the hill levels out, I slow down enough to look beyond the fallen trees I am trying to avoid. Big, wet snowflakes coat my glasses. The boughs of the lodgepole pine and western larch weigh heavy with frozen water vapor. The mountain sky is a single sheet of cloud, so smooth it is hard to find the line between earth and sky.
One more clumsy snowshoe step, and I find myself staring into the deep hole left by the pole of the traveler in front of me. The hole is blue. Ice blue, bubble-gum blue, as blue as the background screen of my new computer. I think about other wild blues I have known—the blue-green of new ice growing on a mountain river, the neon blue of glacier ice. The clear, sunlit sky. How many times have I been given a physics-laden explanation for the cerulean sky? At least as many times as I have forgotten it, and far more than I have understood. But suddenly, running through rolling folds of snow as soft as a giant cumulus cloud, I know in my bones why the distant sky shares this azure with the impression left by a ski pole.
The sky, like the land through which I am wading, is dense with water vapor. The only difference is that the vapor beneath me is frozen, while that above is wild and free in its gaseous form. All day, the sun radiates its bright, electromagnetic spectrum. This band of radiation includes the white light that we see, which is composed of all the colors of the rainbow, each of which has a wavelength all its own. As light travels by wave from our star into the earth’s atmosphere, it strikes the particles flying around in the sky. Light’s collision with water vapor, dust, and other gases results in the scattering of the different hues that comprise it. The long, lazy waves of red and yellow are slow to disperse, and quick to be absorbed by water molecules. Blue, however, with its short wavelength, gets bounced all over the sky. By the time the sun’s light has reached our eyes, most of its components have been taken up by the gases above; blue and violet alone wander the sky.
So, why the blue hole in front of me? The sun’s white light hits the snow and begins its travels full of collision, dispersion, and absorption. The surface snow shines white because light has not yet traveled far enough to be soaked up by the snowflakes. A two-foot depression made by my ski pole, however, reveals how quickly the long-waved colors of the spectrum are absorbed by water. If my poles were long enough to make a five-foot cavity, I would be even more entranced, for the farther that light travels through snow, the more particles there are to take in the undulating reds and yellows. Before long, all that is left to remind us of light’s complexity is a stunning sapphire glow.
Every week since 1991, Field Notes has inquired about Montana’s natural history. Field Notes are written by naturalists, students, and listeners about the puzzle-tree bark, eagle talons, woolly aphids, and giant puffballs of Western, Central and Southwestern Montana and aired weekly on Montana Public Radio.
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