Welcome to brain Stuff from how stuff works dot com where smart Happens. Hi. I'm Marshall Brain with today's question. Is there any way that people could know that the world is a sphere while standing on the Earth? In other words, is the only way to know that the world is a sphere to be up in space looking down on that sphere? Or could you somehow figure this out while standing on a planet that appears at least
superficiently to be flat. If you didn't know that the Earth is a sphere, there are two common observations you could use to convince yourself that it is. The first common observation is the shape of the moon. You see the moon up there every night, and the face of the full moon is circular. That might lead you to believe that it's a sphere rather than a big, round, flat disk. By extrapolation, you could assume that the Earth is a sphere also. But there's a second way that's
more convincing. You would look at how objects in the distance disappear as they get further away. For example, if you had a hundred foot tall sailing ship that's fifteen miles away, it's not visible even if you try to see it with the telescope. That's because it's blocked by the curvature of the sphere. As the ship approaches it rises. First the tip of the mast is visible, then more and more of the ship comes into view as the
ship gets closer. Anyone looking at ships at sea would notice this and they would be able to tell that the Earth is a sphere. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com.