Mohawk Valley Astronomical Society

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Midnight Jewel

by Perry Pezzolanella

The most beautiful sight in a telescope has to be Saturn. It brings awe and wonder to all who see it for the first time and never ceases to amaze the most seasoned observer. The golden globe surrounded by the razor sharp icy white rings is unique and very satisfying, but there is much more that can be seen.

Saturn’s globe is noticeably flattened at the poles due to its low density (less than water) and a rapid rotation of 10 hours and 38 minutes. Saturn is a completely cloudy world with no visible solid surface and only subtle cloud details. The most prominent features are the equatorial zone, equatorial belts, and polar hoods. The belts are areas of sinking atmospheric air that is warming up and drying out revealing a view into the darker depths. The darker clouds are composed primarily of sulfur compounds and water droplets. The zones are areas of rising air that create billowing whitish clouds consisting primarily of ammonia ice. Saturn’s rapid rotation and strong winds over 1000 miles per hour stretch the clouds out into long bands that wrap completely around the planet. The equatorial zone, a wide, bright whitish band that wraps around the equator, is usually partially obstructed from view by the rings, but fully visible when the rings are edge-on. The equatorial belts are the darkest feature that usually appears tan against the golden globe. These are the easiest feature to see with a small telescope but usually only one belt is visible as the rings hide the other. The polar hoods are dusky tan and grade to nearly brown at the poles.

Larger telescopes may reveal delicate streaks within the zones and belts along with brighter oval and darker spots. White spots are subtle but once in a rare while they can be seen in small telescopes. The Great White Spot erupted in 1933 and again in 1990 and 2010. These were temporary as they rapidly elongated wrapping themselves completely around the planet. The huge white spots were bright enough to rival the polar ice caps of Mars in apparent brightness. They are huge, powerful thunderstorm complexes that erupt and billow high into the atmosphere. Ammonia gas rising from the warmer depths freezes out into brilliant white ice crystals higher up.

The rings define Saturn and are an icon as they are the most beautiful feature in the Solar System. They are large but thin, less than a mile thick, and when they are edge-on they seem to disappear. When they are wide open, the dark Cassini Division (or Gap) is easiest to see as a thin, dark line within the rings. The outer ring is not as bright as the inner ring. The shadow of the rings on the globe can often be seen along with the shadow of the globe on the rings, which creates a true 3-D effect!

Up to six moons can be seen with Titan being the most obvious shining around magnitude +8. It orbits Saturn once in about 16 days making it a fun project to plot its motion, especially during a long streak of clear weather. Iapetus is a strange moon orbiting much farther out than Titan with one side as bright as snow and the other as dark as coal. It is easier to see on one side of Saturn than the other as it ranges in magnitude from +10 to +12. Rhea is closer to Saturn than Titan and easier to see and locate than Iapetus as it shines consistently around magnitude +10. Even closer is Dione followed by Tethys with both being a little dimmer than Rhea. The closest moon that can possibly be seen is Enceladus, though a challenge in the glare of Saturn, as it shines at magnitude +11.

Saturn will provide hours of observing pleasure as there is always something changing and worth looking for. Whether it is at a casual star party showing it off to the public, or an intense night of imaging delicate detail in the clouds and rings, Saturn will always satisfy.