2.5- And the earth in all this?
Even a few centuries ago, in the Middle Age, the earth was thought to be flat, and the other celestial bodies -sun, moon, planets, stars, comets, ... were believed to rotate around it in perfect circular orbits. The earth was thought to be the centre of the world mainly or religious reasons.

Philosophers and scientists -like Bruno and Galileo Galilei- were put to death or thrown in prison by the Church to say the opposite that it is the earth that rotates around the sun! Isaac Newton, a religious man, demonstrated that this was the case and his laws of gravity and movements were adopted by most scientists.