It’s that time of year again. Grafton Street is all lit up, the woolly hats and ugly jumpers come out, and there’s a 25 minute delay getting home on the Dart: it’s Christmas. And since there’s a good chance of getting a white December this year, let’s look at some of the weird and wonderful properties of snowflakes that you might not have heard before.
First and foremost, almost all snowflakes are unique. According to physicist Kenneth Libbrecht from the California Institute of Technology, finding two identical snowflakes is like “shuffling a deck of cards and getting the exact same shuffle back. You could shuffle every second for the entire life of the universe, and you wouldn’t come close to getting two of the same.” So while two snowflakes can look strikingly similar, they will never be exactly the same.
Snowflakes form in the clouds from water that has been evaporated from rivers, transpired by plants and breathed out by you. The crystals form in different weather conditions, and from different water sources all over the world. However, the uniqueness of snow is barely scraping the surface of one of nature’s most beautiful marvels. Let’s talk about the shape. Most snowflakes have six-fold symmetry, which means that the snow-crystal can be divided into six equal parts. Try and imagine cutting a snowflake using a straight line and folding it over on to itself, and you’ll get the idea. This hexagonal shape is due to the bonding of the two elements that make up water. A water molecule is composed of two hydrogen atoms and a single oxygen atom, and so when the water cools and freezes, the crystals grow in very specific ways from a central point or ‘nucleus’. Most snowflakes won’t look exactly like the drawing on your Christmas card, but they all seem to have six protruding ‘limbs’, and a hexagon at their core. The shape of snowflakes is also closely related to the weather conditions present in the 15 to 45 minutes it takes for one to form. Crystals being formed in high humidity and -15 °C weather will be beautiful ‘dendrite shapes’ (dendrite comes from the Greek word Dendron, meaning “tree”), while those growing in warmer temperatures and lower humidity may be in the shape of a plate or prism. From a mathematical point of view, snowflakes have been incredibly interesting in terms of studying infinity concepts, and also ‘chaos theory’. One of the most famous snowflakes in existence is known as the Koch Snowflake, which takes its name from the Swedish mathematician Helge von Koch who studied the shape in terms of chaos theory and fractals. The shape regresses on itself infinitely, meaning that the closer we look into the snowflake, we just see the original shape but smaller. Think of placing two mirrors in front of each other and standing between them: the image of your face will become infinitely smaller between the mirrors, but no matter how closely you look you will still see your own head in the glass. This represents the idea of how snow-crystals can behave and form in a theoretical way, but your average snowflake may not be infinite itself. Is snow always the pure white fluff that covers the family car and causes the marquee out back to collapse? There is no doubt that numerous people have told you “don’t eat yellow snow!”, but oddly enough, they’ve been right all along. There have been a few rare cases of discoloured sleet and snow falling from the skies. In February 2002, yellow and orange snow fell in western Siberia. The official report concluded that the snow was in no way dangerous to humans, however the yellow crystals contained levels of nitrogen and iron four times greater than normal. A similar case was reported in March 2006, but this time in Seoul, South Korea. More worryingly these flurries contained heavy minerals, meaning they could pose a serious health risk. In both cases, the rare occurrence of yellow snow was attributed to sandstorms in neighbouring countries and territories. One South Korean meteorological officer was quoted as saying “It’s tough to say whether it’s yellow sand mixed in snow or snow mixed in yellow sand. I have never seen yellow snow falling before.” More recently, there have been reports of brown “dirty” snow in Colorado, USA, due to high winds and dust particles being transferred into the air.
So this winter when you’re having an annual family snowball fight, remember that you are taking a mathematically-influenced crystalline structure that was grown ever-so specifically and matured for almost an hour and cramming it down the back of your younger brothers jacket, or hurling it at your uncle’s face.