first of all - i love it.... and as i'm a bit into astronomy, i love it even more
second - i'm not pro... i'm not even amateur, so my opinion isn't worth even those 2 cents...
all right, my critique:
1) the first thing that struck my eye is the "curve of the motion" - the 4th moon from the left (the "smallest piece") is moved too much to the bottom-right, and that's both optically and also in real (if you take a ruller and make a line between the "tops" of the 2 surrounding moons, this one's below this line, while (if i got it right) should be above)
2) the spaces between the successive moons are not uniform - those moons on the left seem closer to each other than those on the right
3) first 3 moons have each different colour - don't know if it's some atmospheric effect or something, but i think it'd look better if all 3 were "b&w", or in the same colour tone
4) the "curve of motion" seems to me steeper on the left than on the right... i guess that alignment to perfect circular arc would look better...
hope it's helpful, and that my crappy english doesn't ruin everything...
can't wait to see full version
cheers