Saturn (1610–1656): Of the nine planets, four are visible in the night sky without the use of a telescope. Venus, Mars, Jupiter, and Saturn were collectively called the wanderers by the ancient Greeks owing to their sometimes-erratic motions in the night sky. Since these motions were distinct from the predictable patterns of the moon, sun, and stars, these planets were considered to be representatives of the gods. As such they became the foundations for mythology. The faintest of the planets, Saturn, represented the god of agriculture by the ancient Greek, and later the Roman, civilizations.
For most of recorded time the known universe was considered to consist of stars and six heavenly bodies—the sun and moon and the four planets. The invention of the telescope in the 17th century (see TELESCOPE) gave astronomers the ability to observe these objects in greater detail. While Jupiter and Mars would serve as a testing ground for emerging theories on the physical structure of the solar system (see JUPITER; KEPLER’S THEORY OF PLANETARY MOTION; MARS), the dimness and slow-moving nature of Saturn would confine its discoveries primarily to the field of observational astronomy. Galileo was one of the first to observe Saturn using one of the early refracting telescopes. When Galileo first turned his attention to Saturn in 1610, he noticed that the normal spherical planetary disk was marred by small projections on either side. The primitive nature of the early telescopes inhibited Galileo from making more detailed observations, but Galileo proposed that what had historically been considered the planet Saturn was actually a planetary system consisting of three planet-like objects in close proximity to one another. However, unlike the other planets, the shape of Saturn appeared to change over time. In 1612