Sorry for my late answer, didn't have lot of time to play with terragen. Thank you very much for all the answers und tgd files!
I will test it later!
Astaroth
//Edit --> Tested it
@Mr_Lamppost
Okay, it seems that you have used spheres instead of planets. Thank you very much, this solution helps me to get the clouds behind the planet.
But why does this work with spheres and not with planets, and btw whats the difference between them?
Now I get another problem. As you see in my test-renderings, I get lost of the coronas from the suns, when I use spheres, is there any way to get them back?
The pictures gets a bit strange with the spheres :/ It seems that the light goes directly through the spheres...