If you’ve been next to a port lately, or just strolled down a beach and stared off vacantly into the horizon, you might have, perhaps, noticed a very interesting phenomenon: 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.
But – you say – ships do not submerge and rise up again as they approach our view (except in “Pirates of the Caribbean”, but we are hereby assuming that was a fictitious movie). The reason ships appear as if they “emerge from the waves” is because the world is not flat: it’s round.
Imagine an ant walking along the surface of an orange, into your field of view. If you look at the orange “head on”, you will see the ant’s body slowly rising up from the “horizon”, because of the curvature of the Orange. If you would do that experiment with a long road, the effect would have changed: The ant would have slowly ‘materialized’ into view, depending on how sharp your vision is.
If you are caught up on your Navigation history, old ship capitals used to navigate the seas by the stars. They relied on different constellations depending on where they were around the world. This observation was originally made by Aristotle (384-322 BCE), who declared the Earth was round judging from the different constellations one sees while moving away from the equator.
After returning from a trip to Egypt, Aristotle noted that “there are stars seen in Egypt and…Cyprus which are not seen in the northerly regions.” This phenomenon can only be explained if humans were viewing the stars from a round surface. Aristotle continued and claimed that the sphere of the Earth is “of no great size, for otherwise the effect of so slight a change of place would not be quickly apparent.” (De caelo, 298a2-10)
The farther you go from the equator, the farther the ‘known’ constellations go towards the horizon, and are replaced by different stars. This would not have happened if the world was flat: