Rowbotham has a diagram of the sun projecting on the atmolayer on
Chapter 10 here:
Line AB is where the sun projects onto the atmolayer. It seems like it might also be interpreted as a "dome" of atmosphere rather than an line of atmolayer, since the opacity of the atmolayer is all around us in three dimensions.
We should probably make an article about question number 2, "Why can't we see the sun at all times," specifically.
My interpretation of the larger scene would be a large circle representing the circle of the earth, with a smaller circle or oval of the sun's area of light pivoting around its center. The observer's vision is pretty limited, we can only see maybe 25 miles away depending on conditions? Basically a dot. When the border of the sun's area of light intersects the observer's circle of vision sunrise occurs.
Visualization ideas are appreciated.