In 1611, the German astronomer Johannes Kepler showed in his The Strenna or the Sexangular Snow how surprised he was with the complexity of snowflakes . Specifically, he was amazed both by their extreme diversity of shapes, and by the regularity of the branch number of these crystals (6 in total).
Four hundred years later, scientists already understand a little better the different physical principles that drive the formation of scales, although it is true that they have yet to solve all the mysteries surrounding this little miracle of physics.
But how are snowflakes born? Regardless of their shape, all snowflakes are born in the clouds . In fact, when the temperature is low enough, the water droplets that compose them, and whose diameter does not exceed a tenth of the thickness of a hair, can freeze, giving rise to a flaky embryo.
This is when physicists speak of a kind of “germ.” The latter will grow gradually, little by little, absorbing the water molecules contained in the air, thus passing from the gaseous phase to the solid phase, without going through the liquid state.
And scientists wonder if it is possible to find two identical snowflakes. An American physicist at the University of Tucson, specializing in atmospheric sciences, calculated the number of different snowflakes that could exist. Its conclusion? 10 to the 768 different snowflakes; that is, the digit one followed by 768 zeros.
It would be a much higher figure than the one predicted at the time by climatologist David Phillips. In any case, this means that it would be extremely difficult to find two identical snowflakes . Although, as we will see next, it was what happened to Nancy Knight.
And it is that the Guinness Book of Records states that Nancy Knight , a scientist at the American National Center for Atmospheric Research (NCAR), accidentally discovered two identical specimens of snowflakes while she was studying the crystals under a microscope.
And he did it after picking them up from a blizzard that hit Wisconsin in 1988.
Why do snowflakes have 6 branches? It is a property that is linked to the crystallographic structure of ice, whose molecules form hexagons when organized. Thus, its symmetry is inherent in the very structure of matter .
In fact, the hexagonal shape is due to the fact that the water molecules manage to form as many bonds as possible with their neighbors. But the shape it takes will depend on the atmospheric pressure, possibly the electric field present, the water content, the temperature and the wind, among others.
The temperature is decisive for the “silhouette” of each flake, since it will depend on whether it is the upper and lower branches that will tend to grow faster, or the lateral ones.
In this way, all other things being equal, temperatures between -5ºC to -10ºC will give rise to needle-type crystals, and temperatures from -12ºC to -18ºC the crystals will end up forming six-pointed stars.
