According to optical researchers, while we can fool ourselves into thinking we see the curvature of the Earth from high mountains, this is usually wishful thinking. Look there are two ways to see the curvature of Earth, either you go up or you go to a beach.
Earth curvature from space
You should be able to detect it from an aeroplane at a cruising height of around 10,600 metres (35,000 feet), but you need a fairly wide field of view (ie 60 degrees) and a virtually cloud-free horizon. The reality is that clouds, hills and mountains mean we rarely get to see the kind of perfectly flat horizon where the curve would be most obvious.
The true curvature of the earth would be the actual edge of the disk, a great circle of exactly the same diameter as the earth. What you can see from any airplane altitude is a horizon circling you at a few hundred miles away. A small circle. From 35,000′ the horizon is about 230 nautical miles away. So 230nm is the radius of a small circle of the earth’s surface that you can see. To see the actual curvature, which is vastly greater than this circle you would have to be able to see the entire earth. Actual earth-disk circumference is 21,600 nautical miles. Earth’s surface disk visible from FL350 is about 1446 nautical miles.
To claim you can see “the curvature of the earth” from low altitude, like a hundred thousand feet or so, is like putting your eye a couple of thousandths of an inch from a large beachball and believing that you can see its curvature. The math is about the same. What looks curved is that the horizon is about 230nm away at your twelve o’clock but it is also 230 nm away at your eleven, and your one, and your ten, and your two, and your nine, and your three, and so on. If you can see all the way around (as in, from the basket of a balloon) the effect sort of goes away and you again get the sense that you are just hanging above a big (possibly curved) surface. The line of the horizon curves all the way around you, so hanging above a circle it will look curved.
Again, to see the true curvature, you’d have to be able to see the entire near side of the earth.
However, you can detect the curve of the Earth from ground level at the coast with a pair of binoculars – just look for distant ships on the horizon and you’ll see that their hulls start to disappear before their masts and other superstructure. Ancient Greek scientists, who spotted this without any optical aids, used this to conclude that the Earth was round.
Scitech Labs 