Why is snow white?

(from an earlier writing)

Several years ago we had an opportunity to observe North Carolina’s calm, measured reaction to a 12-inch snowfall. The responses ran the gamut from abject fear to screaming panic. We southerners like the way nature handles things and prefer to let old Mr Sun work his environmental magic on the snow. It snows, it melts, dun.

My kids were at an age were they responded with kid-like glee, marveling at our area being so suddenly and completely transformed. But they did come up with the inevitable question: Why is snow white?

Not a bad question when you realize that ice is not white and a close examination of a snow proves it’s composed of only small ice crystals and not cotton, vanilla ice cream or whiteout, that ancient substance used to correct errors in the days of typewriters.

The answer to the mystery is really found in the corollary: Why is anything white? We remember that our so-called white light is really composed of a number of different frequencies of radiation (the spectrum), or so I’m told by Mr. Roy G. Biv (Red-Orange-Yellow-Green-Blue-Indigo-Violet). Materials interact with light in such a way as to reflect back to us all frequencies that are not absorbed. It is these reflected frequencies that give things their color as interpreted by our onboard optical apparatus. If all the incoming frequencies are reflected back to us, we see the object as white; if all frequencies are absorbed, it is black. So, somehow snow is bouncing the entire spectrum right back at us. How?

Ice is not completely transparent; it is translucent. As light passes through the crystals of a snowflake, its direction is slightly altered. The new path is further redirected by the next snowflake and so on, until the light eventually comes back to us (although on different paths, otherwise we would have a mirror effect). The color of all the frequencies in the visible spectrum combined in equal measure is white, so this is the color we see in snow, while it is not the color we see in the individual ice crystals that form snow.