How is Romeo mesmerized by the beauty of Juliet?

When Romeo first lays eyes on Juliet at the Capulet ball, he's immediately transfixed. If there was ever a case of love at first sight, this is it. More than anything, Romeo is drawn to Juliet's incredible beauty, which he expresses in appropriately sensuous language:

Oh, she doth teach the torches to burn bright! It seems she hangs upon the cheek of night Like a rich jewel in an Ethiope’s ear, Beauty too rich for use, for earth too dear (act I, Scene v).

There's something ethereal, almost transcendent, about Juliet's extraordinary beauty, a beauty too good for this world. She outshines all the other women at the ball with her glowing radiance, like "a snowy dove trooping with crows."
Rosaline was just an infatuation for Romeo. But Juliet is (at least according to him) the real thing. Romeo now realizes that he's never truly loved before, and before this fateful night, he'd never seen true beauty either. At this early stage in the play, we're still entitled to regard Romeo's sudden outburst of passion as a sign of youthful immaturity. But subsequent events will confirm the veracity of his emotions and of the extraordinarily powerful effect that Juliet's remarkable beauty has upon him.