Retrograde Motion Essay

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Have you ever looked into the night sky every day for a month to notice that Mars has moved from west to east to west again, that’s retrograde motion. Retrograde motion is a natural occurrence that appears to happen to other planets in our solar system from earth. Retrograde motion is what happens when a planet (we will use Mars as an example) looks as if it is reversing. This occurs when the Earth passes the planet. Direct motion and retrograde motion both occur with Mars, direct motion is when the planet seems to be going forward, and retrograde is when it seems to be going backwards. Many astronomers have noticed this and have tried to come to a solution as to why it occurs. Eudoxus of Cnidus Eudoxus of Cnidus came up with the first theory as to why retrograde motion occurs. He thought that there was a system of spheres, a small sphere in the middle on one axis and a larger sphere on another axis; both of the axis’ are offset. The axis of the smaller middle sphere is embedded in the outer sphere so they share the same motion. Although Eudoxus had come up with an idea people did not agree, one of those people was Cladius Ptolemy. Cladius Ptolemy was the first person to come up with a reason as to why planets have retrograde motion. Cladius Ptolemy was a roman citizen of Egypt who wrote in Greek, he was also a mathematician, astronomer, geographer, astrologer, and a poet. Cladius used the term epicycle to help describe retrograde motion. His model was called epicycle on deferent. In his explanation, the earth is stationary and the planets, moon, and sun rotate and orbit around it. So the line of sight makes it seems as though the planet has stopped and reversed. An astronomer names Nicolaus Copernicus the proved Cladius’ theory incorrect. Nicolaus Copernicus proved Cladius’ theory incorrect. Nicolaus Copernicus was a Renaissance astronomer, mathematician,

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