The sun is simple in a different direction.
If it were visible in the shot, then we would be seeing the shaded side of the ships.
It's not the atmosphere that blocks the stars, but the fact that the Earth and ships are just
too bright and obscure the stars. In fact, in real life even photos taken by Cassini of
Saturn and its moons have too little exposure to see stars (except when the photograph is overexposed).
We're just used to seeing stars in every space-themed piece of artwork we see.
(That, and artistically it's boring to have nothing but black as the background.)
Edit: Slight tweaking. I think it's nearing completion.
As far as text goes - the bottom left corner is very light, and there's nothing but black in the top right.
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