Quote of the Day
Men are born ignorant, not stupid. They are made stupid by education.
— Bertrand Russell (1872-1970). I see lots of problems with this quote, but there is an element of truth in it. I do think that education done poorly can drain all the excitement and wonder out of a child.
I read a lot of nautical history. Many of these history references talk about how sailors have long known the Earth was round. One of the reason why sailors knew the world was round had to do with the appearance of ships and islands on the horizon. Here is a photo that nicely illustrates how the top of a ship is the last part visible as it crosses over the horizon (Source).
Figure 1: Container Ship On the Horizon.
One conundrum that I am unable to answer is this: no matter how wide the field of view, the horizon is always level.
If the Earth is spherical, I would expect to observe a definite curvature of the horizon over large distances. For example, with a view in each direction of say 10 miles, the curvature should give rise to a 66 feet(20m), differential, in each direction. This is more than enough to give a curvature detectable to the eye.
From what elevation of observer would this 66 feet be evident. Since the distance to horizon as viewed from any location would be exactly the same 360 around no curve would be visible below 60000 feet altitude.