If Celestia controlled the moon, and Luna controlled the sun. I tried to make it more interesting than just a straight palette- and cutie mark-swap, dunno how well I succeeded with that. Oh well!
A while ago I realized my headcanon personalities for Celestia and Luna are, like, almost exactly the opposite of what everyone else seems to think.
So somehow that led to this, idk. I think Moonlestia would be called Aurora, but I can't think of a name for Sunluna! Somebody more creative can come up with one.