Thanks a lot, Richard!! Yes, I thought of modeling the rings, but still I wonder, why the shadow of an object is displayed correctly, but leaves this bright area when using an image map in the opacity slot.
And I really like the planet with its atmosphere (I mean the final one in my project. I uploaded only a very simple version)
By the way, in an older thread by you I found a way to use clouds for a planetary ring, but unfortunately the download link is dead. Could you maybe upload it again? I'd love to see, how you managed to use clouds for that.