Radiance

Albeit seen seemingly infinite times, this piece sets itself off the mass positively, resulting in a moderate placement. I will explain what is causing it to not score higher.

Let us start with the most obvious part, even visible in the thumbnail: the colors. You mentioned yourself that this is a tranquil image, and the cold blue is supporting this perfectly. The vastness and loneliness in here is magnificently captured thus.

However, there arises a problem with it. The great majority of space-images is painted in blue tones; this makes your work not stand out at all. Even contrary, it is being pushed back by lower-quality images that offer highlights. A deep blue for the shadows and a warmer hue for the light would have helped greatly.

Talking about the light, it does have some flaws. The top-left corner of the image is drowned in darkness; not a single light-ray is piercing through it. Why? Nothing would hinder the light to cover this area, too. Even worse, it messes up the shadow of the larger planet, seeing that rays close to it vanish, too. Not to mention that a slight reduction of opacity on the large planet's shadow would have helped accentuate the texture.

The volumetric shadow of the small planet is not accurate either. The shadow-stroke has the same width all the way, while the light-rays are not running parallel to each other at all. A more cone-like shape for the shadow would be physically much more accurate. Speaking of accuracy, the lighting of the planet itself suggests that the light source it located in the middle of the right-hand side. Obviously, this is not the case. Additionally, a less opaque planet would have created a better sense of depth for the scene.

Compositionally, this is not the best placement you can have. Everything, planets and light, is located in the top half, leaving a large empty space at the bottom, thus emphasizing the title of the image unnecessarily. The viewer will have issues to focus on a certain part. It is the task of the artist to guide the viewer's eyes through to picture towards a point of interest. Latter is missing; the viewer will follow the light rays, quickly leave the image, and will not look at it again.

The starfield itself if fairly simple and looks more like a placeholder than a vital element of the scene. Except for three bright spots, this seems rather dull and boring. A few flares would have certainly bumped it up. Faint nebulae could have acted similar. Also, slight color variations of the stars do make a difference.

Hopefully, this will help you on your way as an artist.