The name given Saturn, the last of the planets visible to the naked eye to be acknowledged as a planet, is a puzzle. In mythology, Saturn was the god of agriculture; the connection between that entity and the planet Saturn remains obscure, unlike the connection between Mars, the god of war, for example, and the so-called Red Planet, Mars. A clue to Saturn's name may lie in the Assyrian word for Saturn: lubadsagush, which translates to oldest of the old sheep, possibly a reference to Saturn's slow movement through the sky. The Latin name may reflect an association between the planet's slow pace and that of grazing or plowing farm animals.
Italian Jesuit Francesco Maria Grimaldi first noted a key characteristic of the planet in 1645 when he estimated the difference between the planet's polar and equatorial diameters. Saturn is a flattened appearance, and Grimaldi's ratio reflected this: the ratio of Saturn's polar diameter to its equatorial diameter was about 8:9. That calculation meant the planet was indeed flattened, which indicated a rapid rotation about its axis. In 1794 William Herschel tried to determine the planet's rotation by observing a particular point in the cloud belts to see when it returned to the center of the planet. Using this method, he concluded that Saturn had a period of rotation of ten hours, sixteen minutes, and fifty-one seconds. Unfortunately, Herschel also spurred controversy by reporting that Saturn had a square appearance, like that of a bulging cylinder. It was not until 1932 that astronomers proved that the planet's cylindrical appearance was an optical illusion caused by its striking rings, the brightness of the equatorial zone of Saturn, and the shading of the polar areas.
The study of the planet over the last hundred years has paralleled that of Jupiter. Hermann Carl Vogel (1841-1907) analyzed Saturn's spectrum, as he did for Jupiter. Both planets appeared to be made of the same material, and both were thought to have very hot interiors that generated clouds of heated vapors. Christiaan Huygens discovered the first moon of Saturn in 1655, tracking it for several months before concluding it was a moon that traveled around Saturn every sixteen days. Huygens's discovery later became known as Titan; once thought to be the solar system's largest moon, it was been supplanted by Ganymede, a moon of Jupiter, following the Voyager expeditions of the l980s. Discoveries of other moons followed, four by Giovanni Cassini, who at one time pointed out to Louis XIV of France that there were now fourteen objects going around the sun. The king was so impressed with this piece of trivia that he had a commemorative medal struck.
A major difficulty in studying Saturn's moons was numbering them, as astronomers had those in Jupiter's system, since they continued to discover new moons between the orbits of the old. These discoveries periodically necessitated the confused renumbering of Saturn's moons. In 1858 John Herschel (1792-1871) proposed naming the moons after mythological Titans. Titan, the first, has intrigued astronomers because of its large size. In 1944 Gerard Kuiper (1905-1973) determined that Titan possessed an atmosphere; based upon current knowledge, Titan remains the only moon in the solar system to have a substantial one. Nitrogen is the chief component, with methane and possibly argon following.
The Voyager mission to photograph the solar system revealed that Saturn had three additional moons, of which it relayed photos. Titan itself was found to have seas of liquid nitrogen and freezing hydrocarbons.
On three occasions between May 1995 and February 1996, Saturn's rings appeared perfectly edge-on as seen from Earth. This happens only once every thirteen years, and it allows astronomers to take a unique look at the ringed planet. In May 1995, astronomers Amanda Bosh and Andrew Rivkin discovered four new moons orbiting Saturn by observing the planet just at the moment of a ring plane crossing. Because the glare from the bright rings disappears during a crossing, faint objects such as small moons are more easily visible.
Saturn's characteristic rings, like its numerous moons, have long perplexed astromoners, Galileo Galilei among them. His poor-quality telescope revealed a planet flanked on either side by two smaller spheres that he assumed were satellites revolving around the planet. In 1612, however, he viewed Saturn again--this time without its two companions. Cassini had recorded the rings in one of his drawings, but he apparently had only a faint impression of them; other astronomers also noted the dark belts, and William Herschel concluded they were an atmospheric phenomena. Today we know that the rings that looked to Galileo like two spheres on each side of Saturn are visible at different tilted positions as the planet moves relative to the earth. At times they are seen edge-on, nearly disappearing in the process.
Christiaan Huygens was the first to understand the nature of the rings. Using an effective telescope he had constructed himself, he predicted when the rings would next disappear and lived to see those predictions come true. In 1675 Cassini noticed a dark line that split the ring into two concentric portions-- Cassini's Division --which still can be seen today, even with small telescopes. Cassini also offered the first accurate assessment of the ring's composition when he identified it as probably being made up of small particles. In 1980 Voyager 1 revealed a system of over a thousand separate rings, including one seemingly braided ring fifty thousand miles above the planet's surface. Other oddities included lopsided rings, rings with rings and ringlets fanning out from Saturn's surface like a record's grooves, and dark spokes radiating from the planet through its brightest ring. The rings probably average a mile in thickness.
On October 17, 1997, the most ambitious mission to Saturn yet implemented was lauched. Called Cassini, the spacecraft carries an impressive array of experiments designed to probe the atmospheres of Saturn and Titan, as well as to return pictures of unprecendented detail. Unlike Voyager, which sailed through the Saturnian system in one quick pass, Cassini will settle permenantly into orbit amround the ringed planet and its enigmatic moons, giving us a much longer-term look that was possible with Voyager. Cassini will arrive at Saturn in 2004.
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