<P> Some of the moons of Saturn, including Pandora and Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out . Pan and Atlas cause weak, linear density waves in Saturn's rings that have yielded more reliable calculations of their masses . </P> <P> The observation and exploration of Saturn can be divided into three main phases . The first era was ancient observations (such as with the naked eye), before the invention of the modern telescopes . Starting in the 17th century, progressively more advanced telescopic observations from Earth have been made . The third phase is visitation by space probes, by either orbiting or flyby . In the 21st century, observations continue from Earth (including Earth - orbiting observatories like the Hubble Space Telescope) and, until its 2017 retirement, from the Cassini orbiter around Saturn . </P> <P> Saturn has been known since prehistoric times and in early recorded history it was a major character in various mythologies . Babylonian astronomers systematically observed and recorded the movements of Saturn . In ancient Roman mythology, the god Saturnus, from which the planet takes its name, was the god of agriculture . The Romans considered Saturnus the equivalent of the Greek god Cronus . The Greeks had made the outermost planet sacred to Cronus, and the Romans followed suit . (In modern Greek, the planet retains its ancient name Cronus--Κρόνος: Kronos .) </P> <P> The Greek scientist Ptolemy based his calculations of Saturn's orbit on observations he made while it was in opposition . In Hindu astrology, there are nine astrological objects, known as Navagrahas . Saturn is known as "Shani" and judges everyone based on the good and bad deeds performed in life . Ancient Chinese and Japanese culture designated the planet Saturn as the "earth star" (土星). This was based on Five Elements which were traditionally used to classify natural elements . </P>

Who discovered saturn and when was it discovered
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