Circles and PiKepler

Over time, people realised that Earth was just one of many planets orbiting the sun (the Heliocentric model), but it wasn’t until 1609, that the astronomer Johannes Kepler discovered that planets actually move on elliptical orbits.

The sun is in one of the two focal points of these ellipses. The planets speed up as they get closer to the sun, and slow down as they move further away.