Planet is Greek for wanderer. Against the stars, a planet drifts one way, stops, runs backwards for weeks or months, then turns forwards again. Ptolemy explained it with a small circle, the epicycle, riding on a large one. Later, Copernicus explained why it works: the small circle is the Earth’s own orbit, and seen from a moving Earth, every planet is two turning circles added together.

Each loop is a retrograde, the moment the Earth overtakes the planet or the planet overtakes the Earth. The thin rings are the two circles that draw the pattern, and the colored stroke is the planet itself.

Five Planets. Mercury, Venus, Mars, Jupiter and Saturn, the five planets visible with the naked eye. Venus loops 5 times in 8 years, Jupiter 11 times in 12, Mars 15 times in 32, Saturn 28 times in 29, and quick Mercury 41 times in 13.