The curiously looping movements of the planets relative to the stars have presented all sorts of puzzles to keen, patient observers of the night sky. In 1601, Johannes Kepler (1571-1630) undertook the challenge of deciphering the orbit of Mars and developing a mathematical theory of its motion to fit observations of the planet’s changing position in the sky. In assuming that Earth itself traveled around the sun, Kepler’s immediate hurdle was to find a way to disentangle Mars’ motion from that of Earth. He then faced the daunting task of choosing an appropriate geometry for the two planetary orbits so that a line joining Mars and Earth and projected to the stars would correctly mark the position of Mars relative to the stars as seen from Earth. Remarkably, several centuries earlier in Central America, Mayan astronomers had developed their own model to describe the motion of Mars with uncanny accuracy. Anthropologists Harvey M. Bricker and Victoria R. Bricker of Tulane University in New Orleans and astronomer Anthony F. Aveni of Colgate University in Hamilton, N.Y., describe the evidence supporting the Mayan model in the Feb. 13 Proceedings of the National Academy of Sciences.