im pretty sure it means that romeo is comparing juliet to the sun and at the same time to "the moon's handmaiden". he's saying that juliet is "far more fair" than the moon, regardless of it being nighttime or daylight. Thats why he compared her to the sun. when he says "arise fair sun" he is referring to both juliet like i said before, and to the actual sun (because in daytime is when juliet usually would get out and stand in her balcony.) so he wants for the sun to rise and the moon to go down basically
