The nebula is a touch of my own which I will cover in another instructable.
Step 1: The Sky
Create a new layer, and click effects (photo 1)
select gradient overlay, going from #04030e to #140b0b to #1a1515 (photo 2)
Step 2: The Clouds, a Brush.
go to your brush window (photo 1)
select the soft round as your brush (photo 1)
set the brush size to about 500 px (photo 1)
click shape dynamics and follow what I have labeled (photo 2)
Follow the same directions for scattering and transfer (photos 3 and 4)
Uncheck all boxes except shape dynamics, scattering, transfer, and smoothing.
Step 3: The Clouds, the Painting.
Create a new layer, select your brush tool and paint white over the top of your image. (photo 1)
Clouds aren't all white, so create a new layer over your existing cloud layer, and darken your brush, and reduce your flow to about 40. then paint some more clouds near the bottom of the existing ones to act as shadows. (photo 2)
create a clipping mask by holding ALT, or the apple key on a mac, and click between the two layers to make a clipping mask, which should clean up your image nicely (photo 3)
Step 4: The Moon
after you set the moon layer to color dodge, duplicate the layer by selecting the layer, and pressing CTRL+J, or CMD+J on a mac.
Your Document should look like this afterward (photo 3)
Hint: You can move the moon anywhere, and rotate it by pressing CTRL+T on a PC or CMD+T on a mac
Step 5: The Stars, Brush.
follow suit with the rest of the images, but this time include the color dynamics option (photos 2-5)