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

Why Is Siberia's Batagaika Crater Known as the Doorway to Hell?
11:10

BrainStuff Classics: How Would Authorities Handle a Murder in Space?
08:17

How Does Taste Work?
13:59