Well, if you placed your starfield texture on a huge sphere, with the normals facing inwards, that’d give a good result (assuming your shader is up to par).
As for the moon, you could potentially also build it as a piece of geometry, instead of using a moon disc. That way, it could be inside the radius of your star-sphere, meaning it’d occlude the stars correctly.
This is how I have my day/night sky set up, and seems to work pretty well. (Pics TBA)