WORLDS OF ICE
Saturn has some 18 known moons, many being mixtures of ice and rock. Most, however, lie beyond the reach of amateur-size telescopes. The largest is 8th magnitude Titan, visible even in a 3 inch (75 mm) scope. Titan circles Saturn every 16 days, and lying due east or west is about 4 1/2 ring-diameters away from the center planet. This moon is world indeed. At
3,200 miles (5,100 km) it is bigger than the
Mercury. An opaque, atmosphere of nitromethane blankets its
surface, which may feature
lakes of hydrocarbon.
Inside Titan's orbit, other
moons to look for are magnificent 9.9 Rhea, magnitude 10.6 Dione, and magnitude 10.4 Tethys. Careful observation catch the magnitude 11.9 Enceladus.
Be sure not to overloook oddball lapetus. Because its leading side is coated with dark dust, Lapetus is more than twice as bright when it lies west of Saturn than when it lies east of it-ranging from 10th down to 12 magnitude. Lapetus circles otside the orbit of Titan every 79 days at a distance of 13 ring-diameters.