Thanks, that’s very helpful! What I don’t fully understand is the atmosphere. I assume it is a sphere with a slightly larger radius than the surface? If so, I don’t get how the color ramp in the atmosphere shader works, or more precisely, how it produces a soft density gradient only above the earth. If I understand it correctly, the gradient would fall off over the whole radius of the sphere, having almost no effect over the range of the visible object outside the surface. Can you tell me what I miss here? I’m trying to get realistic atmospheres, too, but progress is very slow due to the high render times on my machine (which is why I tried work-arounds like this https://blenderartists.org/forum/showthread.php?376856-Reflection-angle-for-materials&p=2911664&viewfull=1#post2911664 ).
Well done …
The colour ramp node has got nothing to do with it. I just added it as an extra layer of control and I would advise against using it. The effect you’re talking about is the result of the multiply node. Multiplying the output from the gradient texture hardens the edge of the volume as well as scaling up the entire volume. One problems you might face when playing around with the multiply node is that the volume could become larger than the sphere itself and be cut off. The way I got around this was by using a separate empty object (the “Earth atm transform” object) to control the size of the volume. And even if you somehow don’t face this issue I would still use the extra empty as a nice way to control the height of the atmosphere.
Thank you Luftraum 
Thanks for the clear explanation! Very helpful!
Hey Robsorb can you upload the blend file please?
Thank you.