How Far Can You See?

How far can you see is how far humans can see it. I used to assume that the earth was perfectly spherical, including forgetting about mountains. People then do very kindly send in a lot of other suggestions. We don't have visual proof of those theories. No one's bothered to go and check. Or no one's decided to send us the proof. Several people sent me the world record for longest distance in photograph - 270 kilometers. And by the way, thank you to the people who congratulated me on bringing up the question of why didn't you include mountains? Yeah. Didn't include mountains.