How Do We Know:

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How Do We Know the Earth is Round?

Our day to day experience gives us little reason to doubt that we live on a huge, flat, plane. Despite this, all (well, almost all) of us are quite content to accept that the Earth is round. But what evidence do we have that this is the case?

Now there's evidence that's easy to find, there are pictures of the Earth from space. Near real-time images from the DSCOVR satellite available here.

But what evidence predates spaceflight?

Acceptance of a round Earth goes back to the Ancient Greeks. Aristotle (~400 BCE) noted that as one travels north or south the position of the stars changes in the sky. If you go far enough new constellations appear and other disappear. He also pointed out that the shadow of the Earth on the Moon, during a lunar eclipse, always has a round edge. Only a spherical object always casts a round shadow.