When Romeo is in Juliet's garden and she speaks from her balcony (not yet knowing he's there), he says she should speak again because she is "As glorious to this night" as is "a winged messenger of heaven." His imagery here compares her to an angel. He pursues this conceit: the angel is glorious "Unto the white-upturned wondering eyes / Of mortals that fall back to gaze on him." She is an angel above, and mortals look upon her with "wondering" (awestruck) eyes, as they are unworthy to look upon her. 

He also uses the "her eyes are like stars!" simile, but he's a bit more creative in how he presents it: 

Two of the fairest stars in all the heaven,
Having some business, do entreat her eyes
To twinkle in their spheres till they return.

That is, two actual stars had business elsewhere, so they asked her eyes to stand in for them while they were gone. 

There are multiple options to choose from in this scene. Imagery can be defined as vivid and descriptive language that appeals to the reader's senses. In Act 2, scene 2, Romeo spies on Juliet from her garden as she stands on her balcony. The party has just ended and the lovers have realized each other's true identity. Smitten, Romeo has resorted to stalker tactics and Juliet has isolated herself to mourn her new crush. 

Romeo begins Act 2, scene 2, by using light and dark imagery to compare Juliet's beauty to that of the sun's brilliance in the morning. He mentions the moon as a pale imitation to the sun and notes that others must be jealous of how beautiful Juliet is.

He continues to use the light/dark imagery as he compares the twinkling of Juliet's eyes to the stars in the skies and how her cheek's brightness could shame the real stars to dim.