Nowadays it's a given that the earth sits orbiting the sun, but not always! For centuries, in fact you could say not that long ago, we thought the earth was the centre of the universe. I mean why not? We're God's chosen or something right? So to make this a reality lots of people came up with complicated systems to explain it, that didn't really work, then thankfully Copernicus came along and said you're doing it wrong. If you like circles, you'll love this one.