They are what makes skiing and snowman building possible. You squash and bundle them up to make a snowball to throw at a friend. Falling snow conjures happy images of Christmas, children playing and beautiful landscapes. Snow falls all year round in some parts of the world but what exactly is it? Snow is a billion snowflakes all hugging each other. And each of these snowflakes are extraordinary.
Snowflakes are born when cloud droplets, about 10 μm in diameter, freeze into microscopic ice crystals and fall through the Earth’s atmosphere. These droplets remain in liquid form at temperatures lower than −18 °C. In order to freeze, a few molecules in the droplet need to cluster together by chance to form a lattice arrangement. The droplet then freezes around this nucleus. This homogeneous nucleation of cloud droplets only occurs at temperatures lower than −35 °C. Once a droplet has frozen it grows and this is known as the Wegner-Bergeron-Findeison process. They fall through the atmosphere due to their mass and collide and stick together in clusters or aggregates. These aggregates are what we know as snowflakes and are usually the type of ice particle that falls to the Earth’s ground. Snow!
Despite looking white in colour snowflakes are just clear ice. Their white appearance is caused by the diffused reflection of the whole spectrum of light by the tiny ice crystals.
Snowflakes form into a variety of sizes and shapes. Complex shapes are created as the snowflake moves through the differing temperatures and humidities of the atmosphere. The popular belief is that every snowflake is unique. Although statistically possible it is very unlikely for any two snowflakes to appear exactly alike. From 1885 initial attempts to find identical snowflakes by photographing thousands of them with a microscope by scientist Wilson Alwyn Bentley found the wide variety of snowflake types that can form. It is more likely that two snowflakes could become virtually identical if their environments were similar enough. Matching snow crystals were then discovered in Wisconsin, USA in 1988.
The Guinness World Records lists the world’s largest snowflakes as those of January 1887 at Fort Keogh in Montana, USA. One measured 38 cm (15 inches) wide!
In outer space snow is known to occur on Mars. A snow of hydrocarbons is also theorized to occur on Saturn’s moon Titan. While there is little or no water on Venus there is a weather phenomenon which is similar to snow. The Magellan probe imaged a highly reflective substance at the top of Venus’s highest mountain peaks which bore a strong resemblance to terrestrial snow.
The French snowflakes in Val d’Isere were as large as 50p pieces last season…let’s hope they fall larger and in greater abundance next season!