The human eye is basically only limited by the curvature of the Earth and stuff that gets in its way. (Well, and various medical conditions.) Learn how far we can see in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/question198.htm

What Pranks Have Astronauts Pulled?
08:40

How Can Your Body Learn to Tolerate Cold?
10:58

How Did the War of 1812 Settle the American Revolution?
10:23