>>15910888 The Earth is still not flat.
Travelers discovered that they saw different constellations as they traveled north or south. If you look at a model of a celestial sphere, you'll see that with a round Earth at the center, moving north or south changes the set of constellations that you see. For example, as you travel south, you are able to see "new" constellations that cannot be seen from more northern latitudes. They also noticed that ships sailing into view on the horizon had their masts gradually appear as they approached, and that the horizon became further away when viewed from higher elevations on hilltops or mountains. These observations prove that there are parts of the world that are hidden below the horizon no matter which direction you look, which means Earth must be curved in all directions (instead of being cylindrical or doughnut shaped).
They also noticed the curved shadow of the Earth on the moon during a lunar eclipse. If you experiment with shadows from a sphere and a coin, you'll quickly see that the coin gives a round shadow only in a few particular orientations. The fact that the shadow of Earth during eclipses is always curved therefore means that Earth must be spherical, because only a sphere can always cast a round shadow, regardless of orientation.
