Very nice work, and I'm more-so impressed that you can do this by hand! I'm usually one to use GIMP and add a bevel and multiple masks to get the desired effect for depth of a planet's terrain and the "mist"-like appearance of the atmosphere of a planet.

Though I would make the suggestion (and this is totally up to you), the atmosphere should have a bit less in width, ending closer to the planet itself due to the positioning of the star in the picture. And for the moon, I would increase the size of the light reflection from the star, it would be the same concept as a crescent moon or even a solar eclipse as a usual moons surface is covered in a reflective dust. I usually use images of earth and our moon for reference guides when designing an alien world; however, it totally depends on the type of planet you're designing and the designer's point of view such as when comparing our earth atmosphere to a world that has never been touched by industry, I would assume that the atmosphere would be more thick in a horizon picture like yours.

Either way, it looks wonderful!

Thank you very much for the comment and advice, I shall definitely be taking this in consideration, and amazing advice it was. I always had that feeling that something was a little off about the detailing and such. Thank you again!

You're welcome