How do we know Earth is round?

The video explains how Earth's round shape is evident through its shadow on the Moon and the horizon's curvature. It discusses how Earth's rotation creates time zones, with one side exposed to sunlight while the other remains dark. The video also explores the spherical shapes of planets, which allow for equal gravity distribution, contrasting with a hypothetical disk-shaped Earth where gravity would vary.

What new insight or understanding did you gain from this video?