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As Saturn's rings^[1] are the brightest they are considered the jewel of the solar system. Even veteran astronomers can't help but gasp when they see her through a small telescope^[2].

The total number of rings is seven and along their discovery each one was given a letter between A and G for its name. Only three of them are visible from Earth with a telescope and these are A, B and C rings.

1610 is the year when Galileo Galilei became the very first person to observe Saturn's rings, though he could not see them well enough to discern their true nature. In 1655, the astronomer Christiaan Huygens was the first person to describe them as a disk surrounding Saturn. Using a 50 power refractor that he designed himself, Huygens also discovers the first Saturn moon, Titan.

He was also first to observe that every 14 to 15 years the Earth passes through the plane of Saturn's ring and he explains this phenomena in his book, Systema Saturnium, published in 1659.

In 1664 Giuseppe Campani observes that the outer half of Saturn's ring is less bright than the inner half, but fails to recognize this as being two separate rings.

After 17 years when the first Saturn moon was discovered, Giovanni Cassini discovers two new Saturn moons, Iapetus and Rhea, during the ring plane crossings of 1671-1672. Cassini first observed Iapetus in 1671 on the west side of Saturn, but failed to observe it on the east side in 1672 even though he knew it was there. He correctly postulated that Iapetus had light and dark sides, and it always kept the same face turned to Saturn.

Later, in 1676 Giovanni Cassini discovers a gap in the rings which would later be named the Cassini Division. The outer ring would be called the A Ring and the brighter inner ring would be called the B Ring.

Giovanni Cassini discovers two more Saturn moons in 1684, Tethys and Dione, just prior to the ring plane crossing of 1685. It would be over 100 years until the next Saturn moon would be discovered.

Henry Kater reports seeing three gaps in the A Ring in 1825, but no one else could verify Kater's claim for several years. Then in 1837 Johann Encke observes a dark band in the middle of the A Ring^[3] that matches one of the gaps that Kater observed in 1825. This dark band in the A Ring would be later known as Encke's Gap, even though Encke never really observed it as a gap in the rings. Only in 1888 James Keeler becomes the first person to clearly observe the Encke Gap, which Johann Encke saw only as a dark band.

In 1850 William Bond and George Bond observe a dark band across Saturn immediately adjacent to the interior edge of the B Ring^[4]. Charles Tuttle suggests that this might be caused by a dusky ring inside the B Ring. This ring was initially known as the “crepe ring”, because it seemed to be composed of darker material than the brighter A and B Rings. But later it officially became the C Ring. Here is the structure within the C Ring:

Outside rings A, B, C, and D, but lying actually quite close to the A ring, is the narrow F ring. It was discovered by Pioneer 11 in 1979. It was theorized that a thin, narrow ring could be held together by so-called "shepherd moons" -- one orbiting inside the ring and one orbiting outside. Voyager 1 discovered the F ring's shepherds, Prometheus and Pandora, in 1980.

In 1969 Pierre Guerin finds evidence of a possible D Ring.

Outside the D, C, B, A, and F rings are two more rings of a very different character. The G ring (closer to Saturn) and the E ring (farther away) spread out over a much larger vertical distance than the super-flat inner rings. They are also many times more tenuous and transparent than the inner rings.

The E ring was first discovered telescopically in 1967, and its presence was confirmed by the Pioneer 11 flyby in 1979. It is a thick disk of very fine icy or dusty material, with the individual particles only one micron (a millionth of a meter) across. Five of Saturn's seven largest moons are embedded within it: Mimas, Enceladus, Tethys, Dione, and Rhea.

The G ring was discovered by the Voyager 1 spacecraft in 1980. It is extremely thin, but unlike the E ring it is probably made of "macroscopic" particles (that is, particles that you can see without a microscope). Consequently it would be much more dangerous for a spacecraft to fly through the G ring than through the E ring.

Recently around the world, amateur astronomers have noticed that Saturn’s rings are vanishing, they are rapidly narrowing into a thin line.

"The rings have narrowed considerably in the last year," Efrain Morales Rivera reports. "The Cassini division (a dark gap in the rings) is getting hard to see."

Four hundred years ago, the same phenomenon puzzled Galileo. Peering through a primitive spy glass, he discovered Saturn's rings in 1610 and immediately wrote to his Medici patrons: "I found another very strange wonder, which I should like to make known to their Highnesses…." He was dumbfounded, however, when the rings winked out little more than a year later. So what happened?

The same thing that's happening now: a "ring plane crossing." As Saturn goes around the sun, it periodically turns its rings edge-on to Earth—once every 14-to-15 years. Because the rings are so thin, they can actually disappear when viewed through a small telescope.

In the months ahead, Saturn's rings will become thinner and thinner until, on Sept. 4, 2009, they vanish. When this happened to Galileo in 1612, he briefly abandoned his study of the planet. Big mistake: ring plane crossings are good times to discover new Saturnian moons and faint outer rings.

It's also a good time to behold Saturn's curiously blue north pole. In 2005 the Cassini spacecraft flew over Saturn's northern hemisphere and found the skies there as azure as Earth itself. Saturn is a planet of golden clouds, but for some reason clouds at high northern latitudes have cleared, revealing a dome of surprising blue.

For years, only Cassini has enjoyed this view because from Earth, the blue top of Saturn was hidden behind the rings. No more: "Now that Saturn's rings are only open 8 degrees, we can finally view its northern hemisphere's beautiful teal blue colored belts and zones, which really did look blue through my 10-inch telescope," reports Dan Petersen of Racine, Wisconsin, who took this picture on Feb. 24, 2008.

Galileo never understood the true nature of Saturn's rings. He didn't know that they were a disk-shaped swarm of orbiting moonlets ranging in size from microscopic dust to tumbling houses. He didn't even know the rings were rings. Through his 17th-century telescope, they looked more like ears or planetary lobes of some kind.

Yet, somehow, his intuition guided him to make a correct prediction: "they'll be back," or Italian words to that effect. And he was right. Saturn's rings opened up again and scientists resumed their study. In 1659, Christaan Huygens correctly explained the periodic disappearances as ring plane crossings. In 1660, Jean Chapelain argued that Saturn's rings were not solid, but made instead of many small particles independently orbiting Saturn. His correct suggestion was not widely accepted for nearly two hundred years.

Almost 27 ring plane crossings later, we still marvel at Saturn. Even with rings diminished, she is still a breathtaking sight through the meanest of telescopes. Indeed, this is a good week to look. On Tuesday, March 18th, and Wednesday, March 19th, the nearly-full Moon and Saturn will be lined up in the same part of the evening sky. That makes Saturn unusually easy to find: Go outside after sunset and look around for the Moon; Saturn is the bright golden "star" nearby.

NOTES: 1) The rings of Saturn are a system of planetary rings around the planet Saturn. They consist of countless small particles, ranging in size from microns to meters, which form clumps that in turn orbit about Saturn. The ring particles are made almost entirely of water ice, with some contamination from dust and other chemicals.

2)A telescope is an instrument designed for the observation of remote objects and the collection of electromagnetic radiation. "Telescope" (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') was a name given to Galileo Galilei's instrument for viewing distant objects. The name was invented by an unidentified Greek poet/theologian, present at a banquet held in 1611 by Prince Federico Cesi to make Galileo Galilei a member of the Accademia dei Lincei. "Telescope" can refer to a whole range of instruments operating in most regions of the electromagnetic spectrum.

3) The A Ring is the outermost of the large, bright rings. A tiny moon, Atlas, orbits just outside the outer edge of the A ring, which may be why the outer edge of the ring is so sharp. Its inner boundary is the Cassini Division. The A Ring is interrupted at a location 22% of the ring width from its outer edge by the Encke Gap. A narrower gap 2% of the ring width from the outer edge is called the Keeler Gap.The thickness of the A Ring is estimated as 10 to 30 metres, its mass as 6.2×1018 kg (about the mass of Hyperion), and its optical depth varies from 0.4 to 1.0.

4) The B Ring is the inner of Saturn's two brightest rings. Unlike the A ring, which permits some light to pass through it, the B ring is dense enough to be opaque to light. It is so dense that its particles cannot avoid touching each other, and behave more like a fluid than they do like individual particles. The particles appear to be organized into uncountable ringlets, many of which are eccentric (not circular). Many of these ringlets are actually all part of one spiral structure wrapping tightly around and around Saturn, though the B Ring does not contain any gaps.