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Title:Planet of the Month – SaturnDate:2011-4-19
 
Whenever I take the telescopes out to show folks at Star Parties, Sidewalk Astronomy or just those who are interested enough to have a look through – one sight never fails to excite and astound. A person’s first view of the 6th Planet with its amazing ting system – Saturn – never fails to impress.
Saturn, the golden planet of the rings is up in mid-evening every night in March, 2011. It’s nearly at its best for the year – that actually comes next month in April
If you’re not sure how to identify it, watch the eastern sky from 8pm local Australian Eastern Summer Time this month and it will be the yellowish stellar like body that rises first followed closely behind and to the south the bright “disco like” star is Spica.
Just to answer a couple of quick questions – Can you see the rings of Saturn if you look with the eye alone? No, you need a small telescope to see the rings. But, to the unaided eye, Saturn will appear as a bright golden “star” and unlike the twinkling stars, Saturn will shine with a steady light. That might help you identify it.
In ancient Roman mythology, Saturn is the god of agriculture. Saturn is the root of the English word “Saturday”.
Saturn has been known since prehistoric times. Galileo was the first to observe it with a telescope in 1610; he noted its odd appearance but was confused by it. Early observations of Saturn were complicated by the fact that the Earth passes through the plane of Saturn’s rings every few years as Saturn moves in its orbit. A low resolution image of Saturn therefore changes drastically. It was not until 1659 that Christiaan Huygens correctly inferred the geometry of the rings. Saturn’s rings remained unique in the known solar system until 1977 when very faint rings were discovered around Uranus.
Saturn was first visited by NASA’s Pioneer 11 in 1979 and later by Voyager 1 and Voyager 2. Cassini (a joint NASA / ESA project) arrived on July 1, 2004.
Saturn is the least dense of the planets; its specific gravity (0.7) is less than that of water.
Saturn is about 75% hydrogen and 25% helium with traces of water, methane, ammonia and “rock”, similar to the composition of the primordial Solar Nebula from which the solar system was formed.
Saturn’s interior consists of a rocky core, a liquid metallic hydrogen layer and a molecular hydrogen layer. Traces of various ices are also present.
Two prominent rings (A and B) and one faint ring (C) can be seen from the Earth. The gap between the A and B rings is known as the Cassini division.
Though they look continuous from the Earth, the rings are actually composed of innumerable small particles each in an independent orbit. They range in size from a centimetre or so to several meters. A few kilometre-sized objects are also likely.
Saturn’s rings are extraordinarily thin: though they’re 250,000 km or more in diameter they’re less than one kilometre thick. Despite their impressive appearance, there’s really very little material in the rings — if the rings were compressed into a single body it would be no more than 100 km across.
The ring particles seem to be composed primarily of water ice, but they may also include rocky particles with icy coatings.
Saturn’s outermost ring, the F-ring, is a complex structure made up of several smaller rings along which “knots” are visible.
There are complex tidal resonances between some of Saturn’s moons and the ring system: some of the moons, the so-called “shepherding satellites” (i.e. Atlas, Prometheus and Pandora) are clearly important in keeping the rings in place; Mimas seems to be responsible for the paucity of material in the Cassini division, which seems to be similar to the Kirkwood gaps in the asteroid belt; Pan is located inside the Encke Division and S/2005 S1 is in the center of the Keeler Gap. The whole system is very complex and as yet poorly understood.
The origin of the rings of Saturn is unknown. Though they may have had rings since their formation, the ring systems are not stable and must be regenerated by ongoing processes, perhaps the breakup of larger satellites. The current set of rings may be only a few hundred million years old.
 
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