Planetary Epicycles Ceramic Dish: Earth and Mars

The planets’ real paths across the sky, drawn with two circles.

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.

Earth and Mars. Red Mars seen from blue-green Earth loops fifteen times in thirty-two years. Turn the question around, the Earth seen from Mars, and you get the same figure turned half a circle, looping at the same moments.

Who it’s for

This is the real geometry of the night sky: the loops a planet traces as the Earth overtakes it, computed from each planet’s real orbital size and period. Made for astronomers, astrophysicists, physics teachers, planetarium people, stargazers with a telescope in the cupboard, and anyone who loves the history of science.

For a nightstand, dresser or desk, and an easy gift for anyone who loves a good idea.

The Ceramic Dish

• Ceramic, with a wavy scalloped edge and a gold-colored rim.
• About 11.5 cm (4½ in) across and 1.7 cm (¾ in) deep: sized for keys, jewelry and the small things that gather on your desk.
• Hand wash. The gold rim is not microwave or dishwasher safe.

---

Every Zenzicube design is grown from a real piece of mathematics. Find more in the Mathematical Menagerie.