It's actually both. It's a brooch, with a hidden bail for a necklace so it can be worn both ways. It was my mother's birthday gift last year, and so she had something a bit unusual with her birthstone.
No, you're not seeing things. It is the sun, moon and a shooting star (to cover the pin back). The only other thing is the undone finish on it is intentional, it's supposed to be rough still from the casting for the moon rock.