Saturn

Saturn is the sixth planet from the Sun and the second largest: It is 1,429,400,000 km (9.54 AU) from the Sun, with an equatorial diameter of 120,536 km.

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 (and shortly thereafter around Jupiter and Neptune).

Saturn is an oblate spheroid, i.e. it is flattened at the poles and bulges at the equator; its equatorial and polar diameters vary by almost 10% (120,536 km vs. 108,728 km). This is the result of its rapid rotation and fluid state . The other gas planets are also oblate, but to a lesser degree. Saturn is the only one of the Solar System's planets that is less dense than water, with an average specific density of 0.69. This is a mean value; Saturn's upper atmosphere is less dense and its core is considerably more dense than water.

Saturn's atmosphere exhibits a banded pattern similar to Jupiter's, but Saturn's bands are much fainter and are also much wider near the equator. Saturn's winds are among the Solar System's fastest; Voyager data indicates peak easterly winds of 500 m/s (1116 mph).

Saturn's finer cloud patterns were not observed until the Voyager flybys. Since then, however, Earth-based telescopy has improved to the point where regular observations can be made. Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter.