1. 22.1 Early Astronomy

2. Ancient Greeks Astronomy is the science that studies the universe
Deals with properties of objects in space & the laws under which the universe operates
Aristotle – Earth is round bc it always casts a curved shadow when it passes btw the sun & moon
Eratosthenes – established the size of Earth
Hipparchus – star catalog

3. Geocentric Model
Earth was a sphere that stayed motionless at the center of the universe
The moon, sun, & the known planets – Mercury, Venus, Mars, & Jupiter – orbit Earth
Beyond the planets were hollow space, this is were the stars traveled daily around the Earth
Not a correct model

5. Heliocentric Model Sun centered model
Aristarchus was the 1st to believe this model
Earth & other planets orbit the sun
Although there was evidence for this model, the Earth centered model dominated Western thoughts for about 2000 yrs

7. Ptolemaic System Claudius Ptolemy Presented a model of the universe
Accounted for the movements of the planets
Retrograde Motion results in a combination of the motion of Earth & the planet’s own motion around the sun

8. The Birth of Modern Astronomy
Nicolaus Copernicus
Tycho Brahe
Johannes Kepler
Galileo Galillei
Sir Isaac Newton

9. Nicolaus Copernicus From Poland
Convinced that Earth is a planet just like the other five that were known
Daily motions of the heavens could be better explained by a rotating Earth
Changed the model of the solar system to having the sun at the center & the planets (Mercury, Venus, Earth, Mars, Jupiter, & Saturn) orbiting around it

10. Tycho Brahe Born 3 years after the death of Copernicus
Designed & built instruments called pointers which were used for 20 yrs to measure the locations of the heavenly bodies
Brahe’s observations, esp. of Mars, were far more precise than any that were previously made
Johannes Kepler was his assistant

11. Johannes Kepler Discovered 3 laws of planetary motion (pg. 618)
Discovered that the orbit of Mars around the sun was an oval shaped path = eclipse
Mars approaches the sun = speeds up
Mars moves away from the sun = slows down

12. Galileo Galilei Descriptions of the behavior of moving objects
Constructed his own telescope
Discovery of 4 satellites or moons orbiting Jupiter
Discovery that the planets are circular disks
Discovery that Venus has phases just like the moon
Discovery that the moon’s surface was not smooth
Discovery that the sun had sunspots, or dark regions

13. Sir Isaac Newton
Was the 1st to formulate & test the law of universal gravitation
Inertia
Gravitational force decreases w/ distance
Greater the mass of the object, the greater its gravitational force

14. REVIEW REVIEW REVIEW What produces the retrograde motion of Mars?
Location of Earth
Location of Sun
Supporters of Model
Geocentric Model
Center of Universe
________________
Heliocentric Model
Aristarchus, Copernicus
What produces the retrograde motion of Mars?
What major change did Copernicus make in the Ptolemaic system? Why was this change so significant?
In your own words summarize Kepler’s 3 lays of planetary motion.