Why did the ancients fail to discover that the Earth orbits the Sun?
The ancients observed that the Sun and the 'fixed' stars rotated about the Earth. They were also aware that the Earth was spherical. They performed many astronomical measurements on the planets - which are far less 'obvious' than the Sun and the stars. Presumably they knew that the speed of rotation of the Sun and the 'fixed' stars differed and that difference happened to be one day a year. It would seem (in retrospect) obvious that this was no coincidence and no other heavenly motion was so clearly linked to any other. Could they not have deduced that the difference was due to the annual path of the Earth around the Sun?