This is beautiful. My only crit is that the dark clouds seem a bit too much like a slapped on texture in some spots, it doesn't really give the illusion of depth. Everything else is fantastic, I particularly like the lighting on the planets.
This picture has been in my favorites for awhile now; I just thought you'd like to know I used it as a reference when describing the sight of galaxy in fiction story; I credited you and linked back! Here: [link]