THERE are two theories (理论) of the universe. One is called heliocentrism (日心说), and the other is called geocentrism (地心说). Here’s an easy way to remember them. Helios was the Greek god of the sun, so heliocentrism puts the sun at the “center” of the universe. Geo means earth or ground in Greek, so geocentrism puts the Earth at the “center”.