Model of the Solar System

Who is This Greek Guy?

Two models of the Solar System1. 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’

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??

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

2.Nicolaus Copernicus (Late 1400’s):

- Heliocentric Model:Sun centered 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.

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