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Theories of Planetary Motion Part 1: Geocentric Theory.

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Presentation on theme: "Theories of Planetary Motion Part 1: Geocentric Theory."— Presentation transcript:

1 Theories of Planetary Motion Part 1: Geocentric Theory

2 Why should they study Astronomy One main reason… Survival Prepare for climate changes Prepare for climate changes Know when to plant crops Know when to plant crops Know when to harvest crops Know when to harvest crops

3 Geocentric Model Plato: 400 BC Created idea of a “Celestial Sphere” Created idea of a “Celestial Sphere” Sun, Moon, & Planets on separate spheres (26 total) Sun, Moon, & Planets on separate spheres (26 total) Earth is center of all spheres (center of universe) Earth is center of all spheres (center of universe)

4 Geocentric Model Plato (cont.): (Geocentric Acceptance) Earth wasn’t part of the heavens Earth wasn’t part of the heavens Earth wasn’t bright Earth wasn’t bright Little change is the sky night after night Little change is the sky night after night Our senses say we aren’t moving (no wind, objects not left behind, nothing flies off) Our senses say we aren’t moving (no wind, objects not left behind, nothing flies off)

5 Geocentric Model Aristotle: 300 BC Supported Geocentric Model Supported Geocentric Model Added 29 more “Celestial Spheres” Added 29 more “Celestial Spheres”

6 Geocentric Model Aristarchus: 300 BC Student of Plato – proposed idea of the Sun as center of universe. Student of Plato – proposed idea of the Sun as center of universe. Not accepted because: Not accepted because: It violated common senseIt violated common sense Went against religious beliefsWent against religious beliefs He couldn’t explain lack of parallax (shift / movement of an object due to a position change)He couldn’t explain lack of parallax (shift / movement of an object due to a position change)

7 Geocentric Model Ptolemy: 85 – 165 AD Provided theories (mathematically based) to support Geo. Theory Provided theories (mathematically based) to support Geo. Theory Most importantly, he explained retrograde motion Most importantly, he explained retrograde motion -retrograde motion = the apparent backward motion of a planet in the sky.

8 Geocentric Model Ptolemy (cont.) 3 new theories to explain retrograde motion 3 new theories to explain retrograde motion Epicycle= rotational path of planet while circling around earthEpicycle= rotational path of planet while circling around earth Equant= center of deferent (not earth, earth slightly to the side), earth is eccentric (off center)Equant= center of deferent (not earth, earth slightly to the side), earth is eccentric (off center) Deferent= circular path around earthDeferent= circular path around earth

9 Ptolemy’s Theory

10 Ptolemy’s Theory (cont.) Retrograde Motion explained by Ptolemy: Retrograde Motion explained by Ptolemy: Retrograde Motion Animation Retrograde Motion Animation


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