Each one looks small and harmless. And yet snowflakes have had Hamburg firmly in their grip for several days now. As our city experiences its snowiest winter in many years, the question arises: How is a snowflake actually formed?
This is the perfect question for the experts at the TU's Institute for Materials and X-Ray Physics. Among other things, their research focuses on water and how it crystallizes. This ultimately includes snowflakes. But contrary to popular belief, these are more than just frozen water particles floating down from the clouds.
Around 120 basic shapes
“Every snowflake needs a so-called crystallization nucleus,” explains doctoral student Stella Gries. “These are impurities in the air such as fine salts or dust particles. Chemical substances such as sulfur, which have entered the air through exhaust gases, are also possible.” When it is cold enough in the clouds, water droplets attach themselves to these nuclei. “When freezing, water molecules prefer to arrange themselves in such a way that a six-sided structure is formed. Because of this crystal symmetry, the arms and branches of a star-shaped snowflake always have an angle of 60 degrees or 120 degrees to each other.”
But that's just the beginning. “Every snowflake has its own individual path through the cloud,” Stella Gries continues. "Sometimes it's colder or less cold, sometimes more humid or less humid. All of this affects the appearance of the snowflake. There are shapes such as stars, small discs, or needles. A total of around 120 snowflake shapes can be distinguished."
What's more, each snowflake goes through the cycle within a cloud thousands of times. Its size and appearance change again. “It is practically impossible,” summarizes expert Gries, “to find two identical snowflakes.”
Amazing geometry
Gries' colleague Prof. Patrick Huber also deals intensively with the crystallization of water in his work. “All natural phenomena follow mathematical laws,” says the head of the Institute for Materials and X-ray Physics at the Hamburg University of Technology. “Geometric symmetries characterize crystals – and in snowflakes, this order is visible to everyone.”
But can an expert still enjoy the sight of a single snowflake as much as a scientific layman? “I agree with the famous US physicist Richard Feynman” (1918–1988, editor's note), says Patrick Huber. “He was once asked whether a physicist loses his fascination for many things once he knows exactly how they work. Feynman replied: On the contrary – it makes them even more fascinating!” However, it is not known whether Richard Feynman ever had to shovel snow in sub-zero temperatures.
