... Star Trails in Northern Skies . ... As the Earth spins on its axis, the sky seems to rotate around us. ... Aurora Astern . ... Well, probably not ... but it is the most active volcanic moon. Active volcanoes on Jupiter's moon Io were a surprise discovery of the Voyager missions of the late 1970s. Comet-like Clouds in the Cartwheel Galaxy . ... In a cartwheel-shaped galaxy far, far away, huge comet-shaped clouds of gas have been discovered racing through the nucleus at about 700,000 miles per hour. ...