Reasons why the Earth is round and not flat:
- If the Earth was flat, then everybody on Earth would be able to see the same set of stars at night. Very simple research showed that the same stars seen in Egypt cannot be seen in northerly regions at the same time, because the Earth is round.
- If you stick a stick in the ground, it will produce a shadow. The shadow moves as time passes (which is the principle for ancient Shadow Clocks). If the world had been flat, then two sticks in different locations would produce the same shadow, which doesn't happen.
- Planes can travel in a relatively straight line a very long time and not fall off any edges. They can also, theoretically (and some do, though with stops along the way), circle the earth and end up reaching their starting position.
- Then you have time zones. At a certain point when the sun is shining on one part of the Earth, the opposite side is dark, and vise versa. That allows for time differences and timezones, specifically ones that are larger than 12 hours. Thiss would be impossible if the Earth was flat.
- If you looked out onto the ocean, you would see that approaching ships do not just “appear” out of the horizon (like they should have if the world was flat), but rather emerge from beneath the sea. This is because they are emerging from the Earth's curvuture shape.