he sun is small and light from the sun is not visible all the way across the earth, even though it is flat

So the argument is that the sun fades in and out everyday?

Why do we not see gradients, then? (edit)

If that's true, the sun should be brightest when it's directly overhead then noticeably fade until it's gone, like car lights in fog. But that's not what happens.

Every single day the sun is completely visible (barring clouds) from the moment it rises above the horizon to the moment it sets. The only effect of the atmosphere on visibility is to shift the visible light towards the red side of the spectrum and to reflect small amounts of light when it's barely hidden. If the sun "fades out", sunset should take hours, not minutes.

he sun is small and light from the sun is not visible all the way across the earth, even though it is flat

So the argument is that the sun fades in and out everyday?

Why are there not see gradients, then?

If that's true, the sun should be brightest when it's directly overhead then noticeably fade until it's gone, like car lights in fog. But that's not what happens.

Every single day the sun is completely visible (barring clouds) from the moment it rises above the horizon to the moment it sets. The only effect of the atmosphere on visibility is to shift the visible light towards the red side of the spectrum and to reflect small amounts of light when it's barely hidden. If the sun "fades out", sunset should take hours, not minutes.