You make everything by hand? I'm guessing the sun is just a lens flare, but I have
confidence that I couldn't do any real lighting effects with the flare, nor make
a fairly spherical planet. Nice work for a first project, mate.
Edit: To make the star look better, try going back to the original larger picture, and
when you shrink it, try 'contraining proportions' under Image -> Image Size properties.
It downsizes it proportionally, and should make the smaller actually look nicer and sharper.
See if it helps.