Question for September 12, 2009

Geometrically, X can be regarded as an irregular icosagon or 20-sided polygon. Also characteristic is the 90° rotational symmetry and chirality, i.e. the absence of reflectional symmetry.

The ubiquity of X is easily explained by its being a very simple shape that will arise independently in any basket-weaving society. It is a repeating design, created by the edges of the reeds in a square basket-weave. Other theories attempt to establish a connection via cultural diffusion or an explanation along the lines of Carl Jung's collective unconscious.

Another explanation is suggested by Carl Sagan in his book Comet. Sagan reproduces an ancient Chinese manuscript (the Book of Silk) that shows comet tail varieties. Sagan suggests that in antiquity a comet could have approached so close to Earth that the jets of gas streaming from it, bent by the comet's rotation, became visible, leading to the adoption of X as a symbol across the world.

X, in it's original language means any lucky or auspicious object, and in particular a mark made on persons and things to denote good luck.

What's X?