well, is a nice concept, some people might actually make use of this one, the night skyboxes are pretty scarce.

However the resolution is extremely low, as if it wasn´t meant to be used in source, the stars are too big, and the moon looks like a sun, this is more for cs 1.6 and still, there are a lot better detailed skyboxes for gldsource.

In source you can have a texture in any resoltion, so you can edit this in photoshop to fix it up, create a new work sheet with decent resoltuion parameters (1024x1024 is a good size) and now you can remake this, create the dark blueish background, with the paintbrush, draw some nice clouds and simply paint small dots for the stars, redraw the mountains too, is quite simple. As for the moon, google some images of the full moon and use them.

You can make this a lot better, check Komaokc to see top quality source skyboxes.