I want to create a moon and some moonlight being scattered by the clouds. The moon i would guess is just a second planet but i have no idea how to get the light :/
You might find something someone did already in the File Sharing. But, you can make the planet glow different ways. You can turn change the planet's surface shader a number of way, one of which is the Lambert Shader and then experiment. Just try different shaders, even using the image map.
Consider downloading the 'Night Background' here from the forum - do a search for it. It comes with a moon. Overlay the moon over your sun. The visible disc of the sun must be unchecked. This should give you what you are looking for.
Theres a nice moon tgo over at Ashunder in the downloads section