Long before modern science began to understand the processes that create our weather, people made up their own explanations. Many of these accounts were fantastic in nature, with evil or benevolent gods, monsters, and spirits controlling the elements. In this series, we’ll explore some of these ancient myths and share the science behind them. Weather + mythology = weather-ology!
During the holiday season, Jack Frost returns to our collective imagination, along with Santa Claus, Rudolph, Frosty the Snowman, the Grinch, and the rest of our array of favorite seasonal characters. Jack Frost is a mischievous, but mostly benign, figure. Often portrayed as a white-haired, blue-skinned, elven figure, he is said to paint designs on our windows and nip at unsuspecting noses (and fingers and toes) during the winter months.
Jack Frost is best known in North America and Britain, but has his origins in the ancient Norse figure Jokul Frosti, a wicked frost giant who served as the personification of ice and snow. The giants were violent and fearsome foes of both men and gods, a characteristic that makes sense in the light of the chaotic, and often dangerous, power of the weather phenomena they represented. In the related mythology of the Anglo-Saxon people, Jack Frost became less threatening and more of a trickster figure (possibly due to the milder winters experienced in that part of Europe when compared to the usually long, dark, and brutal winters on the Scandinavian peninsula).
While it may be fun to believe that a mirthful sprite cavorts around on cold nights painting elaborate designs on our windowpanes, there is a simple, scientific explanation for why frost crystals form. When the temperature on surfaces — such as cars, windows, blades of grass, and trees — drops below freezing, it causes water vapor on them to freeze. This happens most often on clear, cold nights, when there are no clouds to hold warmth in.
Due to the structure of a water molecule, these tiny ice crystals often freeze intricate patterns. There are actually several different kinds of frost. Rime frost looks like sugar sprinkled onto the edges of leaves and flower petals. It occurs whenever damp winds are coupled with extremely low temperatures. The word “rime” means “crust.” Hoar frost looks like spiky hairs. It gets its name from the word “hoar,” which means “ancient,” because it resembles an old man’s bushy, white beard (much like the one Jokul Frosti would have sported). Hoar frost occurs when water vapor freezes instantly after coming into contact with a very cold surface. Fern frost appears on windows when there is very cold air on one side and moist air on the other. This causes tiny water droplets to form on the cold glass and freeze into patterns that resemble leaves or ferns.
Before people understood the structure of water molecules, the crystalline designs they awoke to find on their windowpanes on cold winter mornings must have seemed like a kind of magic. And so, they imagined a playful winter elf, Jack Frost, must have painted them there.