1000 years before FiM began, Princess Luna grew jealous of Princess Celestia, and so she refused to let the sun shine. She was stopped by Princess Celestia and imprisoned in the moon, but is that the whole story? Isn't it likely that the Elements of Harmony imprisoned Nightmare Moon in stone, like what happened to Discord?

I've heard many people joke about Celestia's overkill in sending her sister to the moon for 1000 years, but given the possible circumstances, I think there might be another reason she did what she did. After all, what sort of punishment do you think the other pony tribes called for for Nightmare Moon's crimes?

(Note: If anyone can suggest a good picture for this, I'd love to look through them.)