Go to the sea and observe boats that are far away and getting closer. You will probably need binoculars. ... let us know what you came up with...
Why can some boats that are really far away be seen with binoculars but not with the naked eye?
Some of them because there are things in the way, like trees, hills, mountains, other boats, the ocean, etc.
You are told that boats sailing away disappear by going up, over and behind curved water three miles away yet when binoculars are used, you can see the boat that just sailed down behind the water. Are you a gullible idiot who believes bullshit or, are you a worthless sack of crap asking misleading questions to perpetrate a lie and a conspiracy?
If you wait a little longer and look with the binoculars, you will find that the boats disappear past the point where they can can be seen even with a telescope. It's because they have passed the aberration point of the air above the water.
People are told by you, and they don't, generally, believe.
Objects converge to a point with distance, this is the vanishing point i.e. boat gone bye-bye. The horizontal line that rises or lowers to eye level (the horizon) is an optical effect that occurs on a plane due to convergence. Perspective is the height or depth the viewer has on or below (submarine) the plane and it affects the distance to the horizon. There's atmosphere and its effects in addition to convergence and perspective, a narrow band mirage forms on top of the horizon line obscuring and mirroring objects, refraction changes the position of objects, compression squishes objects, magnification enlarges & crops objects, diffusion blurs objects.
All of these things are limited, except the actual distance. Distance remains constant. Beyond a certain point, aberration and perspective don't play in, because of distance.
Get the biggest telescope in the world and point it at China. It isn't the aberration or smog that makes it so you can't see China. It's the ground in the way.
The sextant measures angles on plane using the horizon and, distances can be calculated with trigonometry; one minute of arc is one mile. This is proof there is no curve that boats sail over, if the ocean curved the sextant would be useless for navigation and, we would all be forced to watch endless re-runs of Gilligan's Island after the Skipper plots his course. Neither the horizon or the water curves, ever!
That's part of the reason why they have modern telescopes. The sextant isn't capable of handling great distances properly. Sure, it works fine to triangulate nearby locations. But for telling distances and sizes of faraway places, it just isn't accurate enough.
You still believe that
Gilligan's Island was something that really happened, don't you?