So here is my (raw) result:

extra space comet

Finally I've finished the PS part now it's time for some hand painting and Adjustments. I have used basic round brush with flow settings from 30% to 10 % with different blending modes (mostly Vivid Light and Screen).

+ Overall layer Mode is SET TO Linear DODGE.

And here is the result.
DIFFERENCE: Normal < ?> Linear DODGE ? you choose which is better.

extra space comet



extra space comet
   


It all seems to look Unrealistic ? so let's paint a little bit of atmosphere. For this purpose I suggest to use SOFT round brush (+ a new separate layer).

I used basic (hard and Soft brushes with this parameters to create this. + a have also set flow to 1%-7% and here is our result. The illustration is finished.

extra space comet



extra space comet