1. Model of the Solar System

2. Who is This Greek Guy?

3. Two models of the Solar System
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’

4. Geocentric Model Problem:
-Retrograde motion: the apparent backwards motion of planets as a faster orbiting planet passes it.
How did we overcome this??

5. 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
But there was a problem with Ptolemy’s epicycles:
-very complicated; still not accurate in predicting planet positions

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

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