As an Earthling, it's easy to believe that we're standing still. After all, we don't feel any movement in our surroundings. But when you look at the sky, you can see evidence that we are moving. Some of the earliest astronomers proposed that we live in a geocentric universe, which means that Earth is at the center of everything. They said the sun rotated around us, which caused sunrises and sunsets — same for the movements of the moon and the planets. But there were certain things that didn't work with this vision. Sometimes, a planet would back up in the sky before resuming its forward motion.