Early Models of the Solar System: The Movement of Planets

1
Early Models of the Solar SystemThe Movement of
Planets Stars

• Geocentric earth centered models
• Ptolemy (Greek) 150 AD developed his geocentric
  model that the sun, stars, and planets revolve
  around the Earth. His theory lasted 1400 years
  and was adopted by the Roman Catholic Church

2
Ptolemys Model

• a. epicycles- small orbit of a planet

3
Heliocentric Model

• Sun centered model of solar system
• Present day model
• Developed by Nicolaus Copernicus
• (1473-1543)

4
Nicolaus Copernicus (Polish)

• His modeled stated that the Earth traveled around
  the sun in a circular path. Earth was the third
  planet from the Sun
• Model included
• Planets moved counterclockwise
• Earth tilted on axis
• Planets closer to the sun move faster than those
  further away.

5
Retrograde Motion

• Apparent westward loop of a planet in its path
  across the sky
• Occurs because each planet travels around the sun
  at different speeds
• Planet appears to move backward when the Earth
  overtakes it.
• The more distant the planet is the slower it
  changes

6
Tycho Brahe (1546-1601)Dutch

• Supported the geocentric model
• Studied both Copernicus and Ptolemy's models -
  felt that both didnt accurately show the
  position of the planets
• Took very detailed observations on the positions
  of planets and stars 20 yrs.
• Hired Johannes Kepler as his assistant in 1600.

7
Galileo (1564-1642)

• 1st astronomer to use a telescope-1609
• Discovered/Found
• Mts. valleys on the Moon
• Sunspots moving across the Sun
• More stars
• 4 moons of Jupiter
• Documented Venus complete cycle of phases
• Supported Copernicus heliocentric model

8
Johannes Kepler (1571-1630)German

• Inherited Tycho's work
• Supported Heliocentric Model 
• 9 years after Brahes death discovered the
  problem with prior models the shape of the
  orbit was not a circle but an ellipse

9
Keplers 3 Laws of Planetary Motion

• 1st Law - Planets travel in elliptical orbits
  with the sun as the focus.
•  

10
2nd Law - Equal Area Law

1. Speed of a planet around the sun is not constant
2. Planets travel more rapidly when closer to the sun

11
3rd Law is the Harmonic Law

• The time it takes a planet to travel one orbit
  around the sun is called its period.
• P2D3   
• P is the period measured in years
• D is distance in AU (astronomical units)
• Basically - the further a planet is from the sun,
  the longer its revolution

12
What force keeps the planets in motion around the
Sun?

• Kepler thought it was the Sun and its rotation.
• Isaac Newton ties it all together by taking
  Galileos findings and Copernicus/ Kepler
  theories to develop
• Law of Gravitation
• Laws of Motion

13
Sir Isaac Newton (1642-1727)EnglandFrom The
Principia

• All this was in the two plague years of 1665
  and 1666, for in those days I was in the prime of
  my age for invention, and minded Mathematics and
  Philosophy more than at any time.
• Sir Isaac Newton
• The Principia

14
Newtons Law of Gravitation

• Between every two objects there is a force of
  attraction he called gravity.
• Force of gravity between any 2 objects is
  related to the distance between the objects the
  masses of the two objects
• Thought tides were caused by force of moon as it
  revolves around Earth
• Used gravity to explain the long orbit of comets
  proved they are a part of the solar system

15
Newtons 1st Law of Motion

• 1st Law (inertia) an object in motion will
  remain in motion at the same speed and in the
  same direction unless acted upon by an outside
  force.
• Keplers 2nd law, gravity, and inertia together
  explain why the planets continue to revolve
  around the Sun.