a half to thirteen
He is 31,000 miles in diameter , and somewhat heavier , bulk for bulk , than water . Four satellites revolve round him , the nearest , Ariel , being 103,500 , and the farthest , Oberon , 347,500 miles distant . Unlike the orbits of the foregoing satellites , which are nearly in the same plane as the orbits of their primaries , those of the satellites of Uranus are almost perpendicular to his own . They are travelled in periods of two and a half to thirteen and a half days . `` Neptune , invisible to the naked eye , but seen as a pale blue star in the telescope , is 2,780 million miles from the sun , and makes a revolution in 165 years . His diameter is about 35,000 miles , and his density rather less than that of water . `` Neptune has one satellite , at a distance of 202,000 miles , which , like those of Uranus , revolves about its primary in an orbit at a considerable angle to his own in five days twenty-one hours .