Wall of text approaching:
This has the same problem as the Hoth candidate; the lighting is unrealistic to the point of distractiong.
As a piece of art, it's fine. As a background in a 3D space sim where models are otherwise correctly lit, it would look out of place.
There are several ways of creating more realistic border of light and darkness, many of which are found in the Celestial Objects thread in Fan Fiction and Art forum.
Another thing. Consider things like how big that atmosphere is. Endor is most assumedly a gas giant. That means it's likely to be at least 3-4 times larger than Earth in diameter and possibly, even probably much larger considering the observations of exoplanets so far. That means radius in excess of 3x6400km = ~20000 km.
In your image, the distance from center to the edge of the planet itself is 427 pixels, and the atmospheric glow is 53 pixels thick. That means that if the planet has a radius of approximately 20000 km, the atmosphere would be approximately 2500 kilometres thick
for the visible part. The invisible parts would reach even further, so some semblance of realism check could be applied, yes?
This could not happen because the planet's mass would be so large that it would compress into a layer that would have imperceptible thickness from any significant distance, which means that unless you're going for a very, VERY low orbit skybox, you should in my opinion just make the planet's edge crisp but anti-aliased. Observe any available photograph of gas giants from Voyager/Pioneer missions to confirm this if you wish.
Another thing to consider is the curvature of the surface. Currently, the band lines are seen as uniformly aligned, which means the image would be correct if taken from optically infinite distance with a very low field of view. However, as the planet is a sphere, and if you plan on using resolutions like 2048^2, that means you should have the planet fill at least quarter of the sky, at field of view of 90 degrees. And at that distance, you would notice fairly clear spherical effects on the directions of the bands, as well as with any other surface of the sphere. Of course, the curvature effects depend on the angular diameter of the planet, which further depends on the size of the planet and the intended distance from it.
The easiest way to get these things correct is to render the planet to a skybox background in 3D modelling program. In fact I have almost completely migrated to using Blender for the rendering phase of my planets, I just do the texture work in GIMP.
Also one more thing regarding handling of images. Use things like hue/saturation/lightness, brightness/contrast and levels sparingly. 32-bit images have their limitations on how many edits they can take; every edit you take will incur rounding errors into the pixel values, and the effect accumulates very, very fast. This creates effects like banding, which can be seen on especially low lightness, low saturation areas like the blended border of light and dark in that latest posted image. It has some fairly noticeable banding going on in it; similarly the outer edge of the atmosphere is rather sharply defined now as a result of increased contrast.
I can also tell you in advance that if you convert that kind of image into dxt5 it will look rather horrible due to the high amount of large, soft gradients all over the image. This kind of image is very prone to showing dxt compression artefacts and not in a good way. You can try, but you'll notice that it is likely better to use u8888 file format for this kind of planet, no matter how big the image will end up.
Addendum: If this post appears arrogant or deprecating, that is not the intention. I simply have a strong opinion regarding backgrounds and how they should be made, and I sometimes lose the sight of people being new to the craft. I dare say I have a fair bit of practical experience to say what will look good, though, so I feel I can offer some tricks and techniques that can improve the work of people. I don't want to piledrive my own opinions into other people's visions, but I do have a strong interest in seeing geometrically realistic backgrounds in SWC simply because I think that's the way to do things, and will offer the best results in the end...
TL;DR; it's a fine piece of art, but stands improvement in my opinion, and I wouldn't want to see that in SWC simply because I have never seen a planet look like that in Star Wars.
