Sometime around 1609, the great astronomer Johannes Kepler caught what he described as a star from heaven: a snowflake. Its elegant shape inspired him to write A New Year's Gift, or The Six-Cornered Snowflake, for his benefactor, Johannes Matthaeus Wackher von Wackenfels.
In his essay, Kepler rambled amusingly from the seeds of the pomegranate to the cells of the honeybee, picking up clues to the origin of symmetrical natural structures. He was led to a theory for the sixfold shape of the snowflake in terms of the packing of tiny lumps of ice.
The same "indescribable beauty" was admired by the great Irish scientist John Tyndall, of Carlow, in the 19th century. "How imperfect seem the productions of human minds and hands when compared with those formed by the blind forces of nature!" But the blindness is ours, said Tyndall, although he correctly attributed the snowflake's shape to the way molecules of water are arranged in the crystalline structure of ice.
In his book on forms of water, drawn largely from his mountaineering experiences in Switzerland, Tyndall also gave an account of flowers of ice in frozen lakes, which too have a sixfold shape.
Only in recent times was the snowflake adopted as the universal icon of a white Christmas. The earliest example of its use in art is said to be on a 19th-century Japanese sword guard, but the ancient Chinese knew all about snowflakes, so this assertion may well be wrong by some thousands of years.
The snowflake's star-like shape poses a further question. Why does it branch out, in a manner reminiscent of plants? Today we can understand this, too, as a consequence of the growth process in which water vapour freezes on the growing flake.
Depending on the precise conditions, such processes may lead to compact rounded objects or branching feathery ones. If several generations of branches are involved, we may even approach the mathematician's ideal of a fractal structure, one in which detail is contained within detail, indefinitely.
In branching out towards a fractal structure, the snowflake more or less maintains its symmetry. When similar patterns were first found in metals, they were consequently called "iron snow". Other growth processes lead to more random structures, rather like seaweed in appearance.
Treasa Meegan has just completed a PhD in the physics department of Trinity College, Dublin, comparing her computer simulations of these structures with patterns found when metals are electrodeposited. The patterns are found to swirl clockwise or counterclockwise when magnetic fields are applied; the research group, led by Prof Michael Coey, hopes to exploit these magnetic effects.
Dr Meegan also has other talents, including acting: she is starring as Snow White in the Gaiety Theatre's Christmas pantomime. One wonders what Grumpy's remark would be on being told that his house guest is a computational physicist.
Denis Weaire is professor of physics at Trinity College, Dublin, a member of the Royal Irish Academy and a fellow of the Royal Society