Circles and PiOrbits

You might remember from the very beginning of this course, that ancient Greek astronomers believed that the Earth is at the centre of the universe and that the sun, moon and planets move around Earth on circular orbits.

Unfortunately, astronomical observation of the sky didn’t quite support this. For example, the sun appeared larger during some parts of the year and smaller during others. On a circle, every point should have the samean increasinga decreasing distance from its center.