Geocentric Model

Physical Science

1. GEOCENTRIC MODEL Alfredo Meneses III

2. THE PYTHAGOREAN MODEL

3. THE PYTHAGOREAN MODEL In his model, Earth is at rest at the center of the universe and everything rotates around it.

4. Plato’s “Saving the Appearances” Plato adopted the Pythagorean view of the motion of the heavenly bodies as combinations of circular motion about the earth. He assumed that all motions in the universe are perfectly circular and all heavenly bodies are ethereal or perfect.

5. Plato’s “Saving the Appearances” Most of the time, planets move from west to east as predicted. But occasionally, they backtrack for a while; that is, they move westward before resuming their eastward motion or called retrograde motion.

6. EUDOXUS’ MODEL

7. EUDOXUS’ MODEL Eudoxus was the first to “save the appearances” that Plato referred to, using a series of 27 concentric spheres on which the sun, the moon and the planets moved in perfect circular motion.

8. EUDOXUS’ MODEL The breakdown of the 27 spheres is as follows: one sphere for fixed stars, three spheres for the sun, three spheres for the moon, and four spheres each of the five known planets at the time – Mercury, Venus, Mars, Saturn, and Jupiter.

9. ARISTOTLE’S MODEL

10. ARISTOTLE’S MODEL Aristotelian model also used the 27 celestial spheres of Euxodus . In addition, Aristotle used 27 “buffering” spheres between the celestial spheres of Eudoxus and an outermost sphere that was the domain of what he called the Prime Mover. Prime Mover rotated this outermost sphere with constant angular speed, causing the other spheres to rotate as well.

11. ARISTOTLE’S MODEL ~Aristotle divided the universe into two realms-the terrestrial and the celestial-with the orbit of the moon as the boundary.

12. ARISTOTLE’S MODEL Earth is a sphere, he based this proposition on several observations. First, it is only at the surface of a sphere that all objects fall straight down. Second, the view of the constellations changes as one travels from north to south. Lastly the shadow of Earth on the Moon during a lunar eclipse was round.

13. PTOLEMY’S MODEL

14. PTOLEMY’S MODEL The Greek mathematician Apollonius, known in his time as the “The GreatGeometer ,” introduced the idea of an epicycle to explain planetary motion. Apollonius

15. PTOLEMY’S MODEL An epicycle is a circle on which a planet moves. The center of this small circle in turn moves around Earth along a bigger circular path called the deferent. To account for the variation in the speed of the sun during its annual motion.

16. PTOLEMY’S MODEL Greek astronomer Hipparchus refined this model by considering that Earth was off-center or eccentric in the deferent where the sun moved.

17. PTOLEMY’S MODEL Around 140 AD, Ptolemy devised a more complex epicyclic model. He defined a point on the other side of the deferent’s center and called it the equant. The equant and the center of the Earth are equidistant from the center of the deferent.

18. PTOLEMY’S MODEL Ptolemy’s model of the universe survived for more than 14 centuries. The Greeks not only knew that the Earth was round. They also knew the circumference of Earth to be 25 000 miles. Eratosthenes measured it in 235 BCE using trigonometry and the knowledge of the angle of elevation of the sun at noon in Alexandria and Syene (now Aswan, Egypt).