IIRC, the error in considering the extended source as an equivalent point source about the order of (d/D)^2 where d is the diameter of the source, and D the distance you’re viewing it from?
If so, grossly, as the sun’s something like 100 times as far from us as it is wide, so the error, for us globeheads, is not far from 0.01%. So not worth worrying about, idealised averaged point sources are “good enough”.
Of course, in the absence of a concrete model – with numbers – from the globefree ... Read even more
