How Do Scientists Know the Earth Is Round?

Scientists have known for a long time that the Earth isn’t flat. A long time ago, people noticed that ships disappeared below the horizon as they sailed away, like parts of them were being swallowed by the sea! That’s one way to tell the Earth is round. Also, if you go far enough in one direction, you end up back where you started, just like on a ball. Scientists also used the shadow of the Earth during a lunar eclipse, it looked curved, which means the Earth itself must be round too!

Another way scientists figured out the Earth is round is by looking at the moon during an eclipse. When the Earth passes between the sun and the moon, it casts a shadow on the moon. That shadow is always round, like a circle. If the Earth were flat, the shadow would look more like a rectangle or a square. But since it’s round, that helped scientists understand that the Earth must be shaped like a ball!