Is it possible to see behind the horizon because of light refraction? I was debating a flat earther who claims that he was able to see what he shouldn't see if earth was spherical
He stood on a hill with height of 201 m and used his camera to see all of Dubai which was 97 km away, theoritically he shouldn't be able to see anything shorter than 169 meters, however he was able to see everything
I suspect it has something to do with light refraction but i don't know how since he is high enough from sea level, so i hope i find a good explanation
this is the link of the video he made by the way it's just 40 seconds
 A: First of all, if your friend really thinks the earth is flat, then it's going to be very difficult for you to explain this.
Atmospheric refraction can cause light to bend in such a way that you can see things that are physically obstructed by the earth’s surface. When doing calculations as your friend did, it is always important to control for other variables, and refraction is a significant one.
Due to changes in air density in the atmosphere, the speed of light changes and you get refraction. This can mean that images of objects beyond the physical horizon can be raised into view.
On days with minimal refraction, objects that appear to be out of sight can reappear on days where refraction is significant.

Image obtained from Wikipedia - link above.
This image here is an example of such refraction and shows an observer $O$ who can still see the sun appearing to be at position $S'$ even after it has dropped below the horizon (blue line) and is physically located at position $S$.
A: Failure to account for atmospheric refraction has a long history in flat Earther arguments. In the mid 19th century they claimed observations at Bedford Level were proof that the world was not spherical.
Generally atmospheric density and hence refractive index decreases with altitude in the troposphere. Therefore, light rays at a small angle above the horizontal will be bent towards the horizontal. This enables observation of objects physically located below the horizon, which would not be possible without refraction. The image from Wikipedia below shows how this effect leads to the sun apparently setting after it has actually gone below the horizon.

