Reposting an old comment of mine about the Greeks and heliocentrism:

> They "figured it out" but couldn't prove it. The hypothesis had three main issues that weren't solved until scientific knowledge caught up with astronomy:

> 1) Parallax. If the Earth moves around the Sun, then the stars should appear to move back and forth every six months, the same way that a stationary object appears to move when you move your head side-to-side. In fact the stars do show this behavior, but because they're so far away, it's unnoticeable without a telescope. The ancient Greeks believed the stars to be relatively close to Earth, so the parallax should've been much more apparent. Accepting heliocentrism would've meant accepting that the universe was far larger than they thought - they weren't ready to accept that.

> 2) Inertia. The ancient Greeks did not believe that an object in motion will remain in motion. They believed in the concepts of natural motion and disturbed motion, which, among other ideas, posited that force was proportional to velocity. So if the Earth is moving, why do flying birds not slow down and get left behind?

> 3) How can the Earth move? Again, this comes down to the ancient idea of natural motion. In their system of natural philosophy, heavy objects naturally fall to the ground. A heavy object in motion slows down and stops. Earth is the heaviest thing there is - it is literally the element of heaviness. So how can it be in motion? What force is moving the Earth?

> For these reasons heliocentrism was abandoned for 1500 years. It wasn't sacrilegious or anything; it was just deemed to be an interesting hypothesis that didn't stand up to scrutiny.