Well, they could use a lot of work.
First off, before I rate, are you using any stock photos/resources? If you're using anything not made by yourself, make sure that either it's a resource or you got permission from the original artist/owner.
Now, first sig. The moon thing looks really weird. It has strange glowyness (made-up word of the day) and the edges are kinda sharp. The edges of the terrain near where the moon is seen are blurred/faded, which is no good because land is solid. The stars and stuff in the back aren't bad, a little blur could help em out though. The text is not so great though. The terrain in the foreground could use a little sharpening.
On the second one, same thing. Don't fade the edges of the terrain as it gets to closer to the horizon where that sun-thing is. Also, the sun itself is not so great. It needs some solar flares going on in there, and that random black on the bottom right kills it. Could be more spherical and with some more orange as well. The stars in the back are not good either. There shouldn't be that many of them in view with a sun that close, erase the big ones right behind the sun. And lastly, again, don't like the text.
BTW they're not abstract.