Question

how do we know that our earth is round?

Answer 1

our indian ... man aryabhatt says earth is round.... and now all modern scientist believe and all people knows earth is round....
it's is a universal truth.◆●◆●©©©©¶π

Answer 2

The idea of the Earth being a flat disc is also inconsistent with the fact that a given lunar eclipse is only visible from half of the Earth at a time. The only shape that casts a round shadow no matter which direction it is pointed is a sphere, and the ancient Greeks deduced that this must mean the Earth is spherical.

Other than this there are several experiments which proved that the Earth is round.

Hope it helps you and have a great day ahead.