I am incredibly happy with this one!
I've learned so much just in the last few days of making these space pictures.
Edit: I liked the way the main planet came out so much I didn't want to cover it up with shadow, so I used some artist's license and made it visible.
I'm going to say that this is a dual star system and the other star illuminating the main planet is off screen. This may be a cop-out but whatever, it works for me. XD