How can we determine that the earth is rounded, without instruments, just by the power of reasoning?

Question

Without using any instruments, but we may use our senses (eyes, ears, etc.), with the support of reasoning power.

Answer 1

Watch a ship approach a dock. If it's very far away, you see the sails first, before the rest of it. That makes sense if the bottom is slightly out of your field of view due to curvature of the Earth.

Observe a lunar eclipse, where the Moon passes through the shadow of the Earth. You can see the edge of the shadow on the Moon, and it's circular - from everywhere you observe, so the Earth must be a sphere. If it was just a flat circle, the shadow would appear as an ellipse from the wrong angle. But it doesn't.

Answer 2

1. Depends on what you mean by instruments. One of the Greek philosophers figured out the circumference Earth by measuring the length of shadows at noon at different parts of the Earth.

However, just the mere fact that the shadows are different implies that the Earth is round.

2. As discussed by the other posters, the horizon distance increases the higher you go.

3. If you go high enough, you'll actually see the curvature of the horizon

4. Lunar eclipses show the shadow of the Earth on the Moon, and the shadow is completely round

Answer 3

Look at the shadow the Earth casts on the Moon during a Lunar eclipse. It's curved, indicating that the Earth is round.

Doug

Answer 4

Go to the seaside and whatch a boat leave. It disappears slowly from the bottom to the top. Why should we not see it if the earth was flat? We cannot even see it with the strongest of binoculars. (distance dosen't matter).

Answer 5

Sail the world and watch out for those corners and edges.