Awesome, thanks!
I've used the same technique (except I haven't used the crater thing just yet) and the ground is lighting the clouds but I don't get any light in the ground. Even when the luminosity is set to 100.
Another method I used (before I read this) was to create 6 pretty large light sources, set the colour of them to R:255 G:000 B:000 and then set the moon colour to R:000 G:000 B:255, turn off the atmosphere and GI, then used Nuke to colour correct them using the RGB channels.