Assuming you were standing in the middle of the desert, and there were no hills or anything, and everything as far as you could see is flat. Assuming you had amazing superhuman vision, how far, in miles, could you see before the curve of the earth would impede vision?
It was beautiful out today, so I spent some time on the porch with the laptop and a tray table, and I saw a plane far off on the horizon. I figured it had to be five miles up in the air or so, and the sun was setting in the west, and I just sort of let my mind wander and was wondering how far away the plane must have been. How far could I see? Bonus rambling thoughts about the speed of light and how even if the speed of light is 186,000 mps, I was basically seeing the light reflecting off the plane instantaneously, even though it was probably several hundred miles away, because at 186k per second, this thing could be no more than a few hundred miles away, that basically means that the light from the reflection on the plane was there in a fraction of a fraction of a second. Plus, I know planes fly along the curve of the earth, so I just generally confused myself wondering just how far away the plane is. Then I started to wonder about how long it takes the light reflecting off all the things in my yard must take a billionth of a second or less to reach my eyes from ten feet away.
And this, my friends, is why I rarely work outside and prefer a room with no windows when I need to get things done.