Copernicus did not have answers, nor did he have anything to say about what keeps the planets in their orbits or what holds the stars in place. The Greeks had provided such answers, and the answers had stood for millennia. (Each planet occupied a spot on an immense, transparent sphere. The spheres were nested, one inside the other, and centered on the Earth. The stars occupied the biggest, most distant sphere of all. As the spheres turned, they carried the planets and the stars with them.)
