Snowflakes are formed directly from water vapour in the clouds. They skip the liquid state, so to speak. The flakes form their typical shape - six perfectly symmetrical arms - as they fall to the ground, travelling through different temperature and humidity zones.
Snowflakes have many branches and twisted surfaces, they reflect light in different directions. The rays overlap, we see: white. However, according to the so-called thermal spectral range, snow is black. It absorbs almost one hundred per cent of the incident thermal radiation.
So far, no two flakes have been discovered that look completely identical. An ice crystal with a diameter of one millimetre is made up of around 100 trillion water molecules. The probability that all the molecules in two flakes are in the same place is therefore low - but not impossible. It has been proven that they form a variety of shapes. They only ever have six corners or six rays.
You can hear snowfall. How much depends on its intensity and the wind force. Ten decibels are usually estimated for quietly falling snow, which corresponds to the volume of normal breathing. At the same time, the surrounding area becomes quieter because the sound is reflected by the ice crystals and dissipates more quickly.
According to Canadian researchers, snowflakes make a shrill sound as soon as they hit the surface of the water. This is because small air bubbles are trapped in the flakes; when they are released, they produce sounds at a frequency of between 50 and 200 kilohertz. Inaudible to us humans.
Why is it possible to skate on ice and ski on snow? It has to do with the water molecules. The lower the temperature, the slower they become. When water freezes, the tiny particles become almost immobile. But on the very outside of the ice layer, the molecules remain mobile, just like in a liquid. In reality, you are gliding along on a thin film of water when skiing and ice skating.
That the indigenous people of the Arctic have a particularly large number of terms for snow is fiction. Their language is structured very differently, individual words are often difficult to pin down and depend on the context. German, however, has numerous terms for snow. Experts categorise it according to moisture (powder snow, cardboard snow, rotten snow), age (fresh snow, hard snow, penitent snow) or density (floating snow, firn, ice).
Without so-called crystallisation nuclei, no snowflakes form in the clouds. These can be dust or pollen particles, for example. The droplets freeze to these, while at the same time the air around the particles and droplets also freezes.
Firstly, it is 100 per cent sustainable. Secondly, snow conducts heat poorly and the air trapped between the ice crystals insulates. Thirdly, slightly thawed snow becomes as hard as concrete over time and seals well, which is why the Inuit build breathing holes into their igloos. The biggest drawback of the building material: if it gets too warm, it melts rapidly.
Snow is water and therefore odourless. Nevertheless, some people are convinced that they can smell snow. One explanation is that the snowflakes trap aerosols or algae, which have an inherent odour. Another is that snow prevents odours from rising from the ground, so the air "smells" unusually clear to our nose - like snow.
Snow has played a role in many wars. In the eighth century, peasants defeated a Viking prince because they were better able to move through snow-covered Norway on skis. Around 1200, "ski soldiers" were used for the first time in Scandinavia. On 13 December 1916 alone, thousands of soldiers died in the Southern Alps when an avalanche broke loose; during the First World War, some avalanches were deliberately triggered in order to bury the enemy. And the troops of Napoleon and Adolf Hitler got stuck in the Russian snow. Tens of thousands paid for their megalomania with their lives.
Painters love snow. The Impressionists of the 19th century captured snow-covered landscapes on canvas; today this phase is called the "Effet de Neige" (snow effect). Japanese artists even tried to imitate the different colour and light tones of snow with the help of superimposed prints.
To imitate snow in old Hollywood films, directors had white-coloured cornflakes rained over their actors. Unfortunately, these flakes sometimes "snowed" so loudly that scenes had to be dubbed over. Industrial snow is also produced without snow cannons, but by emissions from industrial plants. Snow depths of up to ten centimetres are documented.
The Viennese toolmaker Erwin Perzy opened the first factory for "glass balls with a snow effect" in 1900. He had actually wanted to create a new lamp. But metal shavings swirling around in water reminded him of snow - and prompted him to make the first snow globe.
"Bloody snow" was considered a bad omen in the Middle Ages. But there are two explanations for this rare phenomenon. If the winds carry a lot of Saharan dust with them, red sand particles are sometimes trapped in the flakes. Certain types of algae also colour snow red or green. As with "yellow snow", you should refrain from tasting it.
Nowadays, ultrasound is used to determine snow depths. Depending on how long it takes the sound to travel through the snow, its height can be calculated. However, for the measurement to be accurate, the sensor needs further information, for example on the air temperature.
A single flake weighs an average of 0.004 grams. But it never comes alone, but in masses. One cubic metre of dry powder snow weighs between 30 and 50 kilograms. If it gets wet and compacts, the weight can increase to up to half a tonne per cubic metre. A layer of ice just twelve centimetres thick weighs as much as two to three metres of fresh snow.
Because the individual snowflake is so light, it takes a long time to reach the ground. Without the influence of wind, a flake reaches the ground at a speed of around four kilometres per hour. Even if the flake grows as it falls, i.e. becomes heavier, this hardly matters: the increased surface area slows down the fall.
Due to its structure, snow reflects a lot of sunlight. Without protection, the cornea and conjunctiva in the eye are at risk of burning, similar to sunburn. The resulting snow blindness (medically: actinic keratosis and photokeratitis) can be accompanied by painful visual impairment.
The largest snowflake ever observed is said to have had a diameter of 38 centimetres. Unfortunately, this discovery from 1887 cannot be verified. What is certain is that flakes can grow to gigantic proportions by their own standards by clumping together - according to meteorological reports, they can be between ten and 20 centimetres in size.
In photos, ice crystals look delicate with their many branches. In reality, however, just 275 water molecules are enough to form a flake; real works of art are not yet possible. At higher temperatures, the flakes also become larger and coarser.
Astronomers assume that snowstorms regularly occur on the red planet. However, the snow probably evaporates before it reaches the ground. Instead, there are huge glaciers on Mars - the Korolev crater, for example, more than 84 kilometres in diameter, is covered by a 1.8 kilometre thick ice sheet.
