I can't really test this, but was curious if the path tracer could handle a realistic moon?
A moon, which uses a reflection shader as a child of a surface layer, which is masked by a adjusted grayscale colour of the moon texture with a wide (like 1.5-2) specular spread and a highlight intensity of 10 or something. Very light moon atmosphere with high height limit as a moon glow..
A planet surface with a subtle reflection surface and maybe a lake..
I wonder if you could get a glowing moon all by using the sun, where the moon can actually bounce some light to the planet surface.