'But soft! what light through yonder window breaks? It is the east, and Juliet is the sun! - Arise, fair sun, and kill the envious moon' - What (or who) does Romeo describe metaphorically in this speech from Shakespeare's Romeo and Juliet?

A metaphor states that one thing is something else. This description, however, is too simple for the way metaphors often work in poetry, literature and speeches. You will often find something being described, or written about, as if it is something else, without the writer ever saying 'x is y' (do you see the mathematical metaphor there?).