When Romeo sneaks into the garden beneath Juliet's balcony, he says,
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.
Be not her maid since she is envious.
Her vestal livery is but sick and green,
And none but fools do wear it. (2.2.2-9)
Here, Romeo uses a metaphor to compare Juliet's window to the east, where the sun rises, and he develops this metaphor into another metaphor, by which he compares Juliet to the sun itself. He, likewise, personifies the moon, saying that she feels grief and envy of Juliet, the sun, because Juliet is more beautiful than she, the moon. He expresses his feelings for Juliet, especially concerning her beauty, with these comparisons. Romeo uses apostrophe, speaking to Juliet although she cannot hear him or respond yet, telling her to refuse to be a servant of the moon. He describes the dress of those maids who serve the moon as being a sickly green color and declares that Juliet ought never to wear it.
Romeo goes on to describe Juliet more, saying,
Two of the fairest stars in all the heaven,
Having some business, do entreat her eyes
To twinkle in their spheres till they return.
What if her eyes were there, they in her head?
The brightness of her cheek would shame those
As daylight doth a lamp . . . (2.2.15-21)
Now, he personifies the stars, suggesting that they have some business to which they must attend, and so they ask Juliet's eyes, also personified as something which can understand and respond to questions, to take their places in the sky. He wonders if Juliet's eyes and those stars have actually switched places, emphasizing how brightly her eyes seem to shine. He uses a simile to suggest that Juliet's cheeks are so bright that they shame the stars, just like the daylight shames a lamp because it is so very much brighter than the lamp could ever be. In this simile, the lamp is also personified as something which could feel shame.