why is it not possible to see am entire half of the Earth from space?

Question

I was watching this Vsauce video and Michael [says](https://youtu.be/mxhxL1LzKww&t=4m10s) “international Space Station residents only see about 3% of Earth’s surface at any one time.” He goes on further to [say](https://youtu.be/mxhxL1LzKww&t=22m40s):

> From the Moon, only 49% of Earth’s surface is visible. If you want to see 50%, half of Earth’s surface at once, you have to go even further away. In fact, you have to go infinitely far away which you can’t.

I don’t understand the last sentence when he says “infinitely”. ELI5.

In: 0

Answer 1

Perspective. When looking at a sphere, you can only see the part in front of the points where your line of sight is tangential to the sphere.