Well, this is a problem with the Flat Earth model that has been raised more than once in different forms, but here is my attempt to summarize it.
First let me describe the situation from a RE-ers point of view. On the days of the Spring and Autumn Equinox, the Earth’s axis is perpendicular to the ecliptic. This causes 3 important effects:
1. Exactly half of the globe is illuminated and the other half is in darkness and day and night last equally;
2. the Sun appears exactly at the zenith for an observer situated right on the Equator at noon;
3. The Sun appears to rotate exactly on the horizon in a clockwise or counterclockwise direction for observers situated exactly on the (geographic) North and South Poles, respectively.
This is depicted in the following figure:
On the other hand, the analogous situation on a FE is depicted in the following figure:
The Sun rotates directly above the Equator, so that an observer situated on the Equator would see the Sun at the zenith at noon. The light rays do not undergo aberration because of their perpendicular incidence.
But, you can clearly see that the line of sight from an observer situated on the (geographic) North Pole on the FE builds a non–zero angle with the horizontal. Two solutions are possible:
1. The actual situation is not like it was described;
2. The situation is like it was described, but the connecting line observer – Sun is not identical to the path of the light rays.
I choose not to believe the first one, unless proven otherwise, since it is in direct contradiction to the observations made by every previous generation of observers. So, the second one is our only option (or is it?).
My question is the following: How is the refraction index of the atmolayer to change with altitude so that the tangent to the light ray at the North Pole is horizontal? Note that this must mean the index is smaller at lower altitudes where the density of the air is greater and this is not a regular occurrence. Also, does this explain the day-night pattern depicted on the FE figure?