You have to create two directional lights, and set one of it (the one that will become the Moon) to “Atmosphere Sun Light Index” to 1… or any other number, bigger than zero, as the Index number Zero is usually the sun, or the first directional light. After giving each a different index number, you can control those two lights with this thingie (the second one will crtl + + shift + l +mouse movement), or just set them manually.
Then you alter the second one to a bluegreyish color, intensity to about 0.26 lux (or whatever is good for a dark night, but the docs say this number) and raise the source angle (4 looks quite good for a full moon, especially if you use the Convolution Bloom).
The low Lux number for the Moon is the part, where you need to play with the exposure to prevent a black scene, unless auto exposure does it´s job and adjust it for you.
