Fix a small circle to the rim of a larger one and turn both, following a point on the smallest. Ancient astronomers used these epicycles to predict the wandering of the planets in the night sky. Centuries later, Joseph Fourier showed why they work so well: almost any repeating shape can be built by adding together circular motions of different sizes and speeds.

Star. The five-pointed star, approximately. To get the lines and points exact you'd need an infinite number of circles. This one has twenty-one, so the points are softly rounded and the lines wobble a little.