Front Horizon (desert, buildings, etc) Approximately 800 pixels wide, 200ish tall
Cloudy sky which gets darker as it goes up (I made this by combining 3 images) About 2000 pixels tall, 850 wide
Moon
All four of these are too fast; just for example....The horizon gets darker throughout. The moon travels independently of the sky (so it can start and end whenever you'd want) the whole thing can take 1 second, 20 minutes, etc. The animation will get smoother as the time gets longer.
Let me know if you can use my help. This took me about an hour to build.
Kade