But soft, what light through yonder window breaks?
It is the east, and Juliet is the sun.
— Romeo, Romeo and Juliet · William Shakespeare
Wait — what light is that in the window? It rises like the sun, and the sun is Juliet.
Seeing Juliet at her window, Romeo turns her into daylight itself. The metaphor measures how completely she has become his whole world — and, in a play so full of night, sets his love against a darkness that will finally swallow it.