When I was arriving into what is now my bustling Happy Street, I tapped the full moon (who was smiling) and it turned into a sad looking crescent moon. Now every night I have a sad moon hanging in my sky. Can I ever make it happy again?
Eventually, the moon will stop being sad all on its own, and return to being a happy full moon.
However, tapping on it to make it sad is how you get moonstone, which is useful for crafting some objects in game.