Spell description doesn't seem to mention it.
To what extent? Are you asking if there will be some sort of indication that you have been surrounded by a hemisphere of some sort?
Well, if the enemy has spellcraft they're likely to identify it while you cast it.
Beyond that, I would assume there is some sort of visibility to the barrier, probably a semi-transparent or translucent in nature. It should not hinder sight of or for the creature in any significant way.