Very nice, though the main planet has some odd black dots scattered on it and the moons don't have the lighting colorations as the main planet does. I also wonder whether or not the moons should only be lit up on one side because one or both may be behind the planet in relation to that other sun.
I personally like your starfields better than the planets you have here, because they're of a less common and more unique style than the planet theme is. They're more fantasy-like while the planets are photographic-style (which is good too). But I personally think fantasy space scenes have been done less than photographic and that the duo-planet lit scene although good practice could be a bit more original
Keep up the good work though o/ and I hope my advice helps.