Actually I wanted to write music for background ponies, but then I had so many ideas for Celestia...
Well, here you go. The piece uses two themes that aren't mine:
-The fanfare in the very beginning is from "My Little Pony: Friendship Is Magic" and appears in a few episodes, i.e. season 1, episode 23.
-The melody that plays during the second part is a variation of "Luna" by Eurobeat Brony: www.youtube.com/watch?v=bn7uMwXYU9U

Avgailable on Bandcamp: https://naturematthe.bandcamp.com/track/princess-celestia