1. Model of the Solar System

2. Who is This Greek Guy?

3. Two models of the Solar System 1.Aristotle -Lived more than 2000 years ago in Greece -Geocentric Model: -Earth is the centre of the solar system and all other bodies rotate around it -Earth was stable and motionless -Accepted for over 2000 years -Planets is greek for ‘wanderers’

5. Geocentric Model Problem: -Retrograde motion: the apparent backwards motion of planets as a faster orbiting planet passes it. - Ex. Earth travels around the Sun faster than Mars How did we overcome this??

6. A solution was found by Ptolemy: -Who lived around 140 AD -he proposed the idea of epicycles (small circles) on the planetary orbits and these explained retrograde motion

8. But there was a problem with Ptolemy’s epicycles: -very complicated; still not accurate in predicting planet positions

9. 2.Nicolaus Copernicus (Late 1400’s): - Heliocentric Model: Sun centered model of the solar system

11. Kepler ▫A mathematician ▫Made model more accurate by finding that orbits were ellipses rather than circles Problems: - no knowledge of gravity; still not accurate in predicting planet positions.

12. Clinching Evidence: 1.Galileo (1609) -Developed a telescope -Saw moons orbiting Jupiter 2.Newton (1667) - developed laws of motion and gravity based on Kepler’s work and which are true for earthly and celestial bodies