Thanks Ulco
The moon is just an object about 50.000 high without atmosphere.
Sun is behind the moon for the correct scene illumination (direction).
Moon is additionally lit by a spotlight to get the half moon (fortunately I got no illumination effect of the sun onto the moon object).
In another scene (directly at the pool) I had to place the sun above the moon outside the picture to avoid atmospheric glow and shadows of the moon. But here is was not necessary because anyway the trees are almost black shadows themselves.