Land is too smooth.more islands and rough edges
Now I know you can't make clouds like that in PDN. What'd you use to make them?also the grass on the terrain looks a bit too low res, I think it'd scale better if it was a bit sharper.
I fixed this. First you select gray and black color. Render the clouds, and make them not too sharp (Effects -> Render -> Clouds). Then you click on the layer where you rendered the cloud -> layer properties -> select mode: screen -> done.
Is that moon bigger than the planet itself?
Perspective I think.But even still the moon is far too close to the planet
The picture is a close-up of the moon, with planet Terra in the distance.
I know that. Taking that into account, if you're going for any amount of realism, the moon is still far too close or it's really really small.
You might wanna use images to construct the planet texture if you're aiming for realism.