This is very descriptive and has a lot of meaning. It tells us what Romeo thinks of Juliet and strengthens the idea of Romeo being infatuated by her. He feels that she is unique like the sun and he will never love any other. It is effective as Juliet is on the balcony, which would be the position of the sun. Romeo feels that the brightness of Juliet, the sun, brightens his negative dark life. Romeo also has a fascination with eyes as he keeps talking about Juliet's eyes. I think Shakespeare has done this as the eyes show what the person is emotionally feeling. People's pupils also dilate when they feel attracted to the person they are looking at.
When Juliet appears Romeo says. "It is my lady, O it is my love: O that she knew she were!" and later " O that I were a glove upon that hand, that I might touch that cheek". This hyperbole shows Romeo's obsession with Juliet. Romeo uses romantic language. "Two fairest stars in all the heaven". This shows that he thinks he is in love although the audience are hesitant due to Romeo's relationship with Rosaline, where one minute he loved her and the next he loved Juliet.
Juliet comes out on the balcony and says "Ay me!" Many people are not sure why she says this. I think she yawns as it is quite late after the party and she is tired. Later she says "O Romeo, Romeo wherefore art thou Romeo?" Meaning, "Why are you called Romeo?" This is very plain factual language telling the audience that she is very down to earth. Although she is very practical she says ". Be but sworn my love, and I"ll no longer be a Capulet". This tells the audience that Juliet is interested in Romeo. This is done so that the audience know that this is not just going to be another heartbreak for Romeo.
Juliet doesn't uses imagery very often in this scene but when she does it is very effective for example, " What's in a name? That we call a rose by any other word would smell as sweet".