Shape of the mirrored objectAll lines of sight and lines of perspective converge at the horizon. Depending on our height we cannot see further then the visible horizon. But behind the visible horizon the lines of perspective do continu. As there is to much information aka colours behind the visible horizon there will be mirroring. Normally you will see the sky mirrored on that plane. From our point of view this mirror extends endlessly but will appear as a very small area above the visible horizon. In this mirror ships are visible for a short time, until they disappear from the bottom up due to our "mirrored" line of sight. The most interesting thing about the Sun is that it actually shows how far the mirror extends above the visible horizon. The Sun is mirrored but due to our mirrored line of sight. How this works, you can read in "calculating how long ships are visible cruising over the horizon". As the Sun is mirrored over a great distance and is cut by our line of sight, at the visible horizon it appears smaller. At the moment that the Sun sets in perspective, then it crosses our mirrored line of sight.
Dimensions of Sun and mirrored Sun
When enhancing the Sun at the horizon you can see the mirrored shape just above the visible horizon. It is a very small area but seems to go outward a little bit as it approches our visible horizon. When you measure this it has a ratio of 5,3 at the visible horizon where as the Sun measures 6,8. As in another article on calculating the distance to the Sun, moon and planets I stated that the Sun on a flat earth model would be at a distance of 6207 km with a radius of 28,8 km. This is a diameter of 57,6 km. This would mean that the mirrored Sun at our visible horizon appears to be 57,6/6,8*5,3 = 44,9 km. So over the length of the mirror our mirrored line of sight reduces the size by 57,6-44,9=12,7 km. If you look at one sight of the Sun for triangular calculation it means a reduction of 6,35 km over the distance.
Distance to the Sun
Looking at the photo it appears to be taken just above the waterlevel. So assuming it was taken at eyelevel it was taken at approximately 1,75 m. Assuming also that the visible horizon is at about 5600 m then the distance to the Sun over our line of sight would be 6,35/(tan(tan-1(2/5600))) = 17780 km. I know this method has several vaiables and therefor the answer can be various also. But the point of this method of calculation is that it shows the order of magnitude on how far the Sun would be based on our line of sight. With an average speed of the Sun of 2617 km/hour (spring/autumn) in six hours the sun would travel approximately 15702 km (summer = 1950*8=15600 km). So the forgoing method of calculation actually is a good approximation on how far the Sun is at when crossing the horizon based on our line of sight.
How far is the visible horizon?So if the Sun sets it is at an approximate distance of 15650 km. Based on a eye-height of 2 m how far would actually the visible horizon be? This would result in the following distance to the visible horizon: 2/(tan(tan-1(6,35/15650)) = 4,93 km. This can also be simplified saying distance to the horizon dh=ht/0,40575 with ht is heigt eye in m and dh in km.
PS: this kind of mirroring is only posible on a flat earth model as the plane continu's and continu's as on a globe it would be blocked by the curvature of the earth.
Flat earth or hollow
I do realise that there is one problem with the forgoing theory. There are many many video's in which you actually can see very far over a watersurface using a strong telescope. For instance if you set up a telescope at 0,6 m above waterlevel then based on that on a globe you would see the visible horizon at 2,76 km and on a flat earth model at 1,47 km. Both answer actually don't fit with what we see. There are many video's in which you can see much further than that. If both of these answers are wrong and we can see much further, then this would suggest a hollow earth model with us already on the inside. In that model the sun would also be at the centre of the universe and revolving in 24 hour cirlcles. At the horizon you still would have a small band working as stated as a mirror, after which our line of sight is mirrored even more steep.
Photo: Rijkswaterstaat / Harry van Reeken, https://beeldbank.rws.nl