Flat-earthers like to argue that one can see things further away than one would on a round Earth.  The problem is usually faulty calculations of what one would be able to see.  They don’t consider the height of the observer or the height of what is seen.  The higher up one comes the further one can see.  In addition, higher things can be seen further away.  One has to take into account both.

Otherwise, the plausibility of the claims varies enormously.  Some are counter-intuitive but true while others are true in some cases.  The later only applies under certain specific conditions.  Some are patently absurd and are likely built on misunderstandings if not pure bragging.  Examples form the different categories are:

• You can see Africa from Spain!

Yes, you can see Morocco’s northern tip from the southern tip of Spain.  They are not as far from each other as one might think.  Moreover, there are high cliffs on both sides of the strait.

• You can see Polaris from south of the Equator!

Yes, if you are on the top of Kilimanjaro.  The combination of the mountain’s height and its low latitude makes it possible.  The Tanzanians also maintain it to be the world’s tallest free-standing mountain.  So the view is not hidden by so much more than the Earth’s own bulge.

• You can see the Strasbourg cathedral from the sea!

This would not have been possible even on a flat Earth.  Strasbourg is near the middle of the Western European landmass.  So there would have been too many hills in the way.

In addition, many things are only partially visible.  If the Earth would be flat, why can’t one see all of them?  Perspective can’t hide anything unless there is something else in the way.  In the case of ocean and lake horizons it is about the bulge of the Earth.  Same applies to salt pans which can be markedly smooth.  In all cases one can see more of a mountain or cliff the closer one comes.  However, this can most easily be show on a salt pan.

So why can one see different amounts at different point in time?  Other than the degree of haze and fog there is something called refraction.  Light can bend a little depending on the air it goes through being warmer or colder.  This don’t happen arbitrarily but follows well-documented rules.  Usually this makes things look as if they were higher up.  In some parts of the world a relatively high degree of this is common.  This makes it possible to see islands which would otherwise be beyond the horizon.

Sometimes refraction can make thing look lower instead.  But this requires certain weather conditions which can’t be presupposed every time.  Refraction can't as such explain what the horizon consists of.  Moreover, refraction decreases the higher in the sky one gets.  For more than 30 degrees over the horizon refraction is negligible.  So one does not have to consider this when something is this high up in the sky.

Things can also look to small for us to discern them.  Our eyes have a limited resolution which one has to take into account.  Telescopes and binoculars take light from a small part of one’s field of view and spread it out.  Same applies to the zoom function found in present-day cameras.  They have no upper limit to how far away they can see.  In contrast, they have an upper limit to how much they can enlarge.

Finally, the contrast between light and darkness matters.  A light source can be seen in the dark of night even if the thing the light source sits on can’t be discerned in daylight.  The same effect makes it possible to see the stars at night.  Although larger stars glow brighter their size is not important in and of itself.  Instead, it is how bright they glow and how near they are.  Light does not disappear in space if it does not hit something.  It just spreads out more the further away something is.  So the likelihood of discovering it decreases.

 

Uploaded on the 11th of October 2023.