What is romeo comparing juliet to? And why is the moon envious?

The love that Romeo and Juliet share is the opposite of the selfish love that Shakespeare references in the opening acts of the play. Shakespeare compares Juliet to the sun, and she is one of the most generous characters in the play. She reveals her selflessness when she declares, "My bounty is as boundless as the sea, / My love as deep. The more I give thee / The more I have, for both are infinite" (2.1.175-177). Rosaline, on the other hand, prefers to keep her beauty to herself. Shakespeare heightens this contrast when Romeo describes Rosaline as a Diana (the goddess of the moon) and tells Juliet, "Arise, fair sun, and kill the envious moon" (2.1.46).