[Quite simply, lovesick Romeo is spying on a lovesick Juliet.  Romeo uses numerous metaphors to describe Juliet's beauty here.  Answering this question reminds me, once again, what a master Shakespeare is at his craft, for my paraphrase is no where near as romantic and amazing as the original!  A paraphrase, of course, is a rewording of the original passage.  This being said, here is my true paraphrase beginning from line 2-28:]

Romeo.  Juliet, you are as beautiful and as bright as the sun.  You are so beautiful that you make the moon jealous!  Oh, how I wish Juliet knew that I loved her so much!  I'm down here spying on her, but she's not saying anything!  I wonder why?  She's just standing there with stars in her eyes.  Her beauty is so much more bright than the real stars in the sky that she's staring at.  In fact, if she were in heaven, the birds would think it were day and not night!  That's how bright her beauty is!  Now she's leaning her cheek upon her hand, still looking up in the sky.  I wish I could be a glove on her hand, so that I could touch her cheek!  [Juliet sighs.] She's finally saying something!  Say more!