With all the recent major snowstorms, I find myself almost obliged to write something about the science of snowflakes. (The title of this post, by the way, is the last line in the poem “The Snow-Storm” by Ralph Waldo Emerson.)
Figure 1. Wilson Bentley’s 1902 photographs of snowflakes on black velvet
We have all been amazed by the beauty of six-fold symmetric snowflakes. Although the common phrase “no two snowflakes are alike” is not precisely true, the probability of finding two that are identical is so low that we can safely assume no person will ever see two that are alike in his or her lifetime.
The famous astronomer Johannes Kepler (1571–1630), who discovered the laws describing planetary motion, was so fascinated by the shapes of snowflakes that he devoted an entire treatise, The Six-Cornered Snowflake, to an attempt to explain their symmetry. Unfortunately, the structure of water was not known at Kepler’s time. In addition, Kepler’s scientific views were strongly colored by his religious beliefs. Consequently, he eventually concluded that the shape of the snowflake “existed from the first in the Creator’s design.”
Today we know that the six-fold symmetry of snowflakes is the result of the fact that when water molecules (composed of two atoms of hydrogen and one atom of oxygen) combine to form ice, they form a lattice that consists of hexagons, as shown here:
Image credit: Wikimedia Commons / Solid State
The seed crystals form in the atmosphere around specks of dust, and the six arms grow as the crystal floats through humid air. Since both the temperature and the humidity are roughly uniform across the entire area of a small crystal, the six arms are nearly—but not quite—identical. A careful examination of the snowflakes in Figure 1 will convince you that there are noticeable differences among the arms of a single flake. In particular, larger flakes have more diverse arms, as the crystal grows in somewhat different environments.
You might have thought that by now, we know everything that there is to know about snowflakes, but as amazing as this may sound, we still don’t fully understand the process that makes the six arms of a given flake nearly identical in length. The most plausible theory is that the arms “communicate” with each other through coherent oscillations of the entire snowflake, but the precise mechanism through which these vibrations become coordinated is not fully understood.
To conclude, the next time a snowstorm hits, remember that in addition to the uncertainties associated with weather forecasts, even the structure of those magnificent snowflakes remains somewhat mysterious.
Featured image credit: Istock/Marccophoto
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we on the east coast of the U.S.A. near Boston have gotten so much snow I,m sure there are more than 2 snowflakes that are the exact same!. Hahahaha! and we are going to get even more Snow over this weekend and we already got 78 inches in just 5 weeks!..Help!!!!!.