<P> Hesiod, who wrote in the early 7th century BC, adds the star Arcturus to this list in his poetic calendar Works and Days . Though neither Homer nor Hesiod set out to write a scientific work, they hint at a rudimentary cosmology of a flat earth surrounded by an "Ocean River ." Some stars rise and set (disappear into the ocean, from the viewpoint of the Greeks); others are ever - visible . At certain times of the year, certain stars will rise or set at sunrise or sunset . </P> <P> Speculation about the cosmos was common in Pre-Socratic philosophy in the 6th and 5th centuries BC . Anaximander (c. 610 BC--c. 546 BC) described a cyclical earth suspended in the center of the cosmos, surrounded by rings of fire . Philolaus (c. 480 BC--c. 405 BC) the Pythagorean described a cosmos with the stars, planets, Sun, Moon, Earth, and a counter-Earth (Antichthon)--ten bodies in all--circling an unseen central fire . Such reports show that Greeks of the 6th and 5th centuries BC were aware of the planets and speculated about the structure of the cosmos . Also, a more detailed description about the cosmos, Stars, Sun, Moon and the Earth can be found in the Orphism, which dates back to the end of the 5th century BC, and it is probably even older . Within the lyrics of the Orphic poems we can find remarkable information such as that the Earth is round, it has an axis and it moves around it in one day, it has three climate zones and that the Sun magnetizes the Stars and planets . </P> <P> The name "planet" comes from the Greek term πλανήτης (planētēs), meaning "wanderer", as ancient astronomers noted how certain lights moved across the sky in relation to the other stars . Five planets can be seen with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn, the Greek names being Hermes, Aphrodite, Ares, Zeus and Cronus . Sometimes the luminaries, the Sun and Moon, are added to the list of naked eye planets to make a total of seven . Since the planets disappear from time to time when they approach the Sun, careful attention is required to identify all five . Observations of Venus are not straightforward . Early Greeks thought that the evening and morning appearances of Venus represented two different objects, calling it Hesperus ("evening star") when it appeared in the western evening sky and Phosphorus ("light - bringer") when it appeared in the eastern morning sky . They eventually came to recognize that both objects were the same planet . Pythagoras is given credit for this realization . </P> <P> In classical Greece, astronomy was a branch of mathematics; astronomers sought to create geometrical models that could imitate the appearances of celestial motions . This tradition began with the Pythagoreans, who placed astronomy among the four mathematical arts (along with arithmetic, geometry, and music). The study of number comprising the four arts was later called the Quadrivium . </P>

Who had the knowledge of 5 planets mercury venus mars jupiter and saturn
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