The phrase "what light through yonder window breaks" is a line from William Shakespeares play Romeo and Juliet. It is spoken by Romeo in Act 2, Scene 2, as he sees Juliet on her balcony. The line is a poetic way of asking where the light is coming from and is followed by a metaphor comparing Juliet to the sun in the east. The full quote is "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, Who is already sick and pale with grief, That thou her maid art far more fair than she".