1. Chatfield Senior High Physics
History of Astronomy

2. Plato (4th C BC) Stars represent the heavens and are perfect
Sun, planets, and
stars move in
the “perfect” circle

3. Aristarchus (3 C BC)
First to propose the sun-centered universe (heliocentric)
Not accepted because objects seemingly orbit around us

4. Ptolemy (150 A.D.) Proposed the Earth-centered (geocentric model)
Must use circles for orbits, but must account for orbits as observed in the sky

5. Retrograde Motion of Mars

6. Ptolemaic Model (Geocentric)

7. Copernicus ( )
Proposed the well accepted Sun-centered (heliocentric) model
Not simpler than the earth centered due to circular orbits

8. Copernican (heliocentric) Model

9. Tycho Brahe ( )
Danish nobleman with a telescope set-up in his castle
He observed planetary objects with great accuracy and over a long span of time

10. Tycho Brahe’s Castle

11. Tycho Brahe’s Stellar Map

12. Johannes Kepler ( )
Used Tycho Brahe’s observation of Mars to develop a mathematical approach for orbital mechanics

13. Kepler’s 1st Law
A planetary orbit is an ellipse with the sun at one focal point

14. Kepler’s 2nd Law
Planets sweep out equal areas in equal times

15. Kepler’s 3rd Law Periods and distance of orbits are related
T is period in years
R is the average radius of orbit in
astronomical units (AU)
k is 1 for any planet orbiting the sun

16. Applications of Kepler’s Laws
We will get to Mars through using the basic premises of these laws

17. Galileo ( )
Galileo attacked the Catholic Church’s belief of a geocentric universe through scientific proof

18. Dialogue of Two World Systems
This published document used satire to challenge the authority of the Catholic Church

19. Moon craters
Challenges perfection of heavens

20. Galilean Moons of Jupiter
Moons orbit Jupiter instead of the Earth

21. Galileo’s Finger!

22. Isaac Newton ( )
In addition to the three laws of motion he developed the law of universal gravitation

23. Law of Universal Gravitation

24. Focus of Unit Kepler’s Laws of Motion as applied to Mars
Newton’s Law of Universal Gravitation
Space exploration focusing on how spacecraft and eventually man will go to Mars