ok, honestly my first thought was round, but if you think about it, what else in the game is round.. maybe just the tops of trees? well anyways, next point - the clouds are square, youd have to make clouds rounded and what not if you did the sun and the moon and then what next? - next point - you can mod in a round moon/sun if you really want a round sun or moon - my buddy has a realistic sun and the majoras mask moon in his.. looks pretty sweet, anyways point is, you can mod it. im going to have to go with square to keep minecraft from becoming a jumble of patchwork styles.