Romeo is of course speaking metaphorically here; Juliet is not the sun, and it is still night in the orchard. But Romeo states the comparison with such devotion that it should be clear to the audience that, for him, it is no simple metaphor. For Romeo, Juliet is the sun, and it is no longer night. Here is an example of the power of language to briefly transform the world, in the service of love.
And yet, in the same speech, Romeo and Juliet also question the power of language. Wishing that Romeo were not the son of her father’s enemy, Juliet says:
’Tis but thy name that is my enemy.
Thou art thyself, though not a Montague.
What’s Montague? It is nor hand, nor foot,
Nor arm, nor face, nor any other part
Belonging to a man. O, be some other name!
What’s in a name? That which we call a rose
By any other word would smell as sweet.
Here Juliet questions why Romeo must be her enemy. She refuses to believe that Romeo is defined by being a Montague, and therefore implies that the two of them can love each other without fear of the social repercussions. But language as an expression of social institutions such as family, politics, or religion cannot be dismissed so easily because no other character in the play is willing to dismiss them. Juliet loves Romeo because he is Romeo, but the power of her love cannot remove from him his last name of Montague or all that it stands for. In the privacy of the garden the language of love is triumphant. But in the social world, the language of society holds sway. This battle of language, in which Romeo and Juliet try to remake the world so that it would allow for their love, is one to keep an eye on.