"Ears," Rings and Cassini's Gap

No one can say what keen-eyed observer in the dawn of history first picked out Saturn as a planet, or heavenly wanderer, from the dizzying background of myriad fixed stars. Probably the first stargazers to leave a record of Saturn's appearance in different parts of the night sky were the Sumerians.

They lived in southern Mesopotamia about 5,000 years ago and, according to George Michanowsky, a scholar of cuneiform writing, they called the planet Sag-Ush, regarding it as a male fertility symbol. The Babylonians, who eventually ruled over that part of Mesopotamia, watched the heavens from the tops of their ziggurats. To them Saturn was known as Kaiamanu (the steadfast one), possibly because, in contrast to nearer planets, it moved so slowly across the skies. Kaiamanu was generally associated with the death of cattle, and other calamities. Perhaps in hopes of better luck, one of the names the Egyptians later gave Saturn was Horus the Bull.

The fiery imagination of the Greeks created more elaborate tales about the golden planet. The Greeks called it Cronus, after the evil-tempered son of Earth and Heaven, who married his sister Rhea and devoured five of his own children because he feared them as rivals. Finally, when Zeus, the sixth, was born, Rhea tricked Cronus into swallowing a stone instead. After he was dethroned by Zeus (who became the king of the gods), Cronus went off to rule another kingdom, where he reformed his ways and taught people the secrets of planting. The Romans knew Cronus as Saturn, and as a god of fertility and planting. Every Dec. 17 they staged the Saturnalia in his honor. At this time there was gift giving, drinking and wenching and suspension of punishment for criminals.

Some ancients also watched the planets out of sheer intellectual curiosity. Ptolemy, one of the greatest of the Greek astronomers, wanted nothing more than to explain the eccentric wanderings of the five known planets: Mercury, Venus, Mars, Jupiter and Saturn. Why, for example, did Saturn seem at times to forge ahead of Jupiter in the sky, and at other times lag behind it? To fit this movement into the prevailing earth-centered view of his day, Ptolemy assembled meticulous records of planetary movements. In A.D. 140, he made a good guess about Saturn. Because of its slow pace, he deduced that it lay in the most distant of the heavenly spheres. Thus astrology gave way to astronomy.

It took another 1,400 years, and the invention of the telescope, before Saturn was really established as a planet. In July of 1610, Italian Astronomer Galileo Galilei contemplated Saturn through a new, 8-power spyglass. He was stunned. The familiar planet seemed to have sprouted ears or handles. Galileo assumed that Saturn's ears were moons like those of Jupiter, which he had discovered only a few months earlier. But when he looked again, some time later, he got another surprise: the moons had vanished. Whimsically, he asked: "Has Saturn, perhaps, devoured his own children?"

Half a century passed before Galileo's question was answered. In a 1659 treatise, Systema Saturnium. Dutch Astronomer Christiaan Huygens correctly deduced the the ears of Saturn were a distinct ring, disconnected from the parent planet and slightly tilted as observed from the earth. From a terrestrial perspective the ears would periodically vanish because the angle of vision changed during Saturn's voyage around the sun. A superb telescope-maker, Huygens also discovered Saturn's largest moon, Titan, and calculated the time it took the ringed planet Huygens make a single journey around the sun (nearly 30 years). Wryly, Huygens speculated about the people who might inhabit these cold distant worlds: "It is impossible but that their way of living must be very different from ours," he wrote, "having such tedious winters."

The other great pioneer among Saturn watchers was the 17th century Italian-French more Jean Dominique Cassini. He located and named four more satellites (Iapetus, Rhea, Dione and Tethys). But Cassini's place in the heavens, and in was history of astronomy, rests on the discovery of a gap in what was then presumed to be a solid, opaque ring around Saturn. Other moons, as well as rings, were up in the intervening centuries, bringing the number up to a dozen. It took Voyager 1 to reveal that the "Cassini division" was not a gap, but many more rings.

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