Saturn , sixth planet in order of distance from the Sun, and the second-largest in the solar system. Saturn's most distinctive feature is its ring system, which was first seen in 1610 by Galileo, using one of the first telescopes. He did not understand that the rings were separate from the body of the planet, so he described them as handles (ansae). The Dutch astronomer Christiaan Huygens was the first to describe the rings correctly. In 1655, desiring further time to verify his explanation without losing his claim to priority, Huygens wrote an anagram, the letters of which, when properly rearranged, formed a Latin sentence that read in translation, “It is girdled by a thin flat ring, nowhere touching, inclined to the ecliptic.” The rings are named in order of their discovery, and from the planet outward they are known as the D, C, B, A, F, G, and E rings. They are now known to comprise more than 100,000 individual thin rings, each of which circles the planet.
As seen from Earth, Saturn appears as a yellowish object—one of the brightest in the night sky. Observed through a telescope, the A and B rings are easily visible, whereas only under optimal conditions can the D and E rings be seen. Sensitive ground-based telescopes can detect the brightest of its numerous satellites, and in the haze of Saturn's gaseous envelope, pale belts and zones parallel to the equator can be distinguished.
Three United States spacecraft have enormously increased knowledge of the Saturnian system. The Pioneer 11 probe flew by in September 1979, followed by Voyager 1 in November 1980 and Voyager 2 in August 1981. These spacecraft carried cameras and instruments for analysing the intensities and polarizations of radiation in the visible, ultraviolet, infrared, and radio portions of the electromagnetic spectrum. The spacecraft were also equipped with instruments for studying magnetic fields and for detecting charged particles and interplanetary dust grains.
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