The Secret Life of Snow
A bizarre and fascinating world of icy plates, needles, and six-armed flakes emerges from the lab of Eric Erbe and William Wergin
by Ivan Amato
From the February 2004 issue, published online February 5, 2004
 A
|
|
FROSTY SYMMETRY Crystal shapes are as diverse as the environments that created them. Crystals that form in two temperature ranges—from 27°F to 32°F and from –13°F to 18°F—are shaped like hexagonal plates (A). Air closer to 32°F yields columns and needles (B). The familiar six-armed snow crystals, technically known as dendrites (C), grow in vapor-rich air between 3°F and 10°F. Detailed views of such crystals (D) clarify the relationship between atmospheric conditions and the snow crystals they produce. Extreme magnification, well beyond what is shown here, reveals airborne particles trapped in the crystals, which could provide a new way of studying acid snow and air pollution. Despite its fame, the six-armed crystal is just one of the many dozens of identified crystal forms. It became the archetypal image of snow largely because of the work of Wilson Bentley, a Vermont farmer who spent the winters between 1885 and 1931 outside his house photographing snow through a light microscope. Due to the low resolution of this technique, and also to Bentley’s aesthetic preferences, he mostly photographed the large, symmetrical star-shaped flakes—the ones that are now reproduced ad infinitum on greeting cards and in newspaper ads. The sixfold symmetry reflects the way that water molecules link up into a hexagonal lattice as they freeze, a molecular pattern blown up to macroscopic scale. |
