Can someone remind me how shadows in the ground prove the curvature and roundness of the Earth?

Question

I know shadows in the ground prove how the Earth is positioned close the Sun and how the light reflects off the moon and something to do with the curvature of space and/or roundness of Earth but can someone give me a quick overview? Something to do with the roundness of Earth creates shadows.

Also, for the stupid Flat Earthers, I know flat land or flat surfaces don’t experience as many shadows or very rarely, but yeah can someone explain?

Thanks for helping the random thought.

In: 1

Answer 1

Carl Sagan gave a good easy-to-understand explanation on his show Cosmos: https://www.youtube.com/watch?v=G8cbIWMv0rI&ab_channel=carlsagandotcom

Basically, a Greek guy noticed that if you have the sun directly overhead from you (your shadow stays right under you), then a stick pointing straight up from another location on Earth has its shadow pointing off to the side instead of right under it. This only makes sense if we are on a round object, so things pointing “up” are really pointing “out” from the center in different directions. If you know how far it is between yourself and the stick, and you can measure the angle the stick’s shadow makes, you can figure out about how big the earth has to be in order for the shadow to make that angle. He got a number within a few percent of the real value thousands of years ago.