What's funny about Copernicus not understanding that the planets orbits were elliptical is that it must have been clear that the moon's orbit around Earth is. The Antikythera mechanism models an elliptical orbit for it, so it must have been obvious. Now, it's not obvious that the moon's orbit around the Earth is like that of the planets around the Sun, but it doesn't take much imagination to think that orbits are similar in nature regardless of what is being orbited.