I came up with a pretty super easy way to do it with splats.  No other software required but C either (coolness!).

I'll build a tutorial and post a scene to the free stuff.

Great, theres a video at Youtube using image as backdrops. Splats are a great thing since it point to camera always, but we cant see the preview for it.

 Nice!

Well, maybe I'm a little out of date here using the term "splat".  I'm simply using a single square poly with a texture mapped to it.  I'm calling it a "splat".  When I post the tutorial, it will all be straight forward.

Great! Looking forward to it

Very effective use of "splats". Looks great.

Well Carrara have splat as primitive objects.

so it's like an APS background layer behind the sky, excepting the sky itself has no transparency
after exporting the tiff from carrara, hence one couldn't use those planet images in APS.

Here's a screen capture of the scene.  You can see my "splats" as dark gray squares.

Thank you Kixum!

You can go and get the files in the freestuff section (that's been approved).  I'm still waiting for the approval on the tutorial.

There are two files.  One for generating the image for the "splat".  The other is just a scene where the splat is hung in the sky.

And now the tutorial is approved in the tutorial section.

Go and hang the moons and planets to your hearts desire!