Alone in the universe

First, a bit of critique. I think the planet could have used a bit more work. You seem to use the same planet texture in all of your pieces, and the fact that it's the Earth makes it a bit too "in your face." There are some really great tutorials for creating planet textures on your own, as well as many fantastic stock planets that you should really take advantage of. I also think you could have spent a bit more time on the atmospheric glow; I like to create multiple layers underneath the planet for the outer glow by gaussian blurring a white circle of the same size as the planet to different extents. That helps to give the glow a nice falloff effect. For the atmospheric glow visible over the surface of the planet I use a combination of inner glow, inner shadow, and a couple of additional layers set to overlay, linear dodge, and/or color dodge.

Now, I have to say that this image, at the display size, is absolutely beautiful. The angle of the lighting on the planet seems spot-on, and your muted color palette is very soothing. The understated flare works very nicely, as does the very subtle background. I particularly love the dark side of the planet, and the soft city lights.

The detail isn't there for me to set this as my wallpaper, but I spent a good few minutes looking at it, which says a lot (for me). Great work!