Informant38

Until very recently anyone looking at the sky would see, in the day, something solidly blue, and at night darkness punctuated by tiny lights. Two bodies wheeling across the sky east to west from horizon to horizon, both exactly the same size, one burning so bright it hurt to look at it, the other cold. Both occupying .5 degrees of the celestial arc.
Except for the differences in color and intensity between the sun and moon, none of these things are true.
The sky isn't blue, you can't go up there and get a piece of it and come back with something blue, and the night sky isn't dark, not in the way it seems.
And of course the sun and the moon aren't the same size at all.
Their functions are mirror opposites. One goes around the earth, the other the earth goes around, one is a source of light, the other only reflects it.
The night sky appears dark, and it's so counterintuitive to think otherwise even people with scientific educations will argue the point, but a simple thought experiment shows it's filled with light, everywhere.
Stand in the desert and look at a star, say Alpha Centauri. Then go stand on the moon and look at it, while someone takes your place on earth and looks at it at the same time.
Now leave someone in your place on the moon and go stand on Mars and look at it, while the other two look at it from the earth and the moon.
Each one sees the light of the same star at the same time, because the light of that star is everywhere around us, as is the light from every other visible star. All around us, anywhere there's line of sight.
So there must be a sphere of light coming from each one. We're bathed in starlight - it may seem like little dots, it may seem like there's only the line of it coming toward you that hits your eye, but like the blue sky and the same size moon and sun that's no more than an illusion.
The most fundamental appearance of what surrounds us is illusion.