This ornament nearly passes muster for Katie
Andrii Oleksiienko/Shutterstock
At the moment of yr, every little thing appears to be adorned with some type of seasonal design – bushes, holly, jolly Santas and so forth. One form you typically see is a snowflake. Sure, they’re lovely and complex, however I can discover their proliferation deeply annoying.
The form of snowflakes is an artefact of the chemical construction of ice, and although (as they are saying) each snowflake is exclusive, there’s truly a surprisingly common mathematical sample in there too. We frequently use the language of symmetry to explain shapes. If one thing has reflection symmetry, we are able to draw a line throughout it, and the shapes on either side can be mirror pictures of one another.
A form may have rotational symmetry – we are able to partially rotate it and get the identical form. The variety of completely different positions on the way in which spherical that end in the identical form is known as the order of the symmetry: a form like a sq. has order 4 rotational symmetry, whereas an equilateral triangle has order 3.
Some shapes simply have rotational symmetry (just like the three-legged emblem of the Isle of Man) and a few simply have reflection symmetry (like a stick determine, which has a single line of reflection down the center).
Common polygons have each rotation and reflection symmetries – referred to as dihedral symmetry – and we are able to mix these symmetries to get others. For instance, reflecting a sq. vertically then horizontally equals a rotation by 180 levels. In the identical means we add collectively numbers, there are additionally methods to “add” symmetries to explain what occurs while you mix them – a part of an space of maths referred to as group concept.
The snowflake is an ideal instance: it has the construction of a hexagon, which may be mirrored alongside six completely different strains passing by means of the centre of the form, and rotated by 60 levels six occasions. This symmetry arises as a result of chemical construction of water and ice. The angle between the bonds is such that when the water freezes, the molecules – held collectively by hydrogen bonds – prepare themselves right into a inflexible hexagonal lattice.
This chemistry signifies that the overwhelming majority of ice buildings, together with snowflakes, have an underlying hexagonal form. The precise type of the snowflake is determined by the circumstances beneath which it varieties, together with temperature, humidity and stress – that means all of them have tiny variations, however the identical underlying construction.
As a mathematician, I’m very happy within the winter to be surrounded by shapes with such a chic construction, even when it’s too small to see. However I’m additionally deeply pissed off by decorations (not the one proven!) depicting snowflakes with eight (boo) or 5 (ugh) branches. Be vigilant, readers: beware the seasonal snow-fake!
These articles are posted every week at
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Katie Steckles is a mathematician, lecturer, YouTuber and creator primarily based in Manchester, UK. She can be adviser for New Scientist‘s puzzle column, BrainTwister. Comply with her @stecks
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