Refuting the Flat-Earth theory

[FlatAssembler]

Here is how Flat-Earthers explain away the constant size of the Sun: https://theflatearthsociety.org/tiki/tik...+at+Sunset

do airplanes also stay of a constant visual size as they move from the zenith to the horizon?    or does it require the sun-ness of the light to affect this extremely convenient phenomenon?

The apparent sizes of airplanes are almost always so small you cannot see them changing size. Flock of birds also don't change their apparent sizes much as they approach the horizon. So I don't understand your question.