1. Topic: Models of the Universe Key Terms: Geocentric Theory Heliocentric Theory

2. Geocentric Theory Ancient Greece

3. Geocentric Model ___

4. Motion of the other planets Mars Retrograde Motion

5. Geocentric Model: Ptolemy (87-150 AD) Used epicycles to explain planetary movements

8. Retrograde Motion

9. Ptolemy’s system provided the first framework for all discussion of the universe for nearly 1500 years!! But… there was a problem…

10. Problems with Geocentric Theory 1.This model does explain apparent motions of celestial (space) objects 2.Cannot explain Foucault’s Pendulum or the Coriolis Effect

11. Heliocentric Theory

12. Heliocentric Model ___

13. Copernicus (1473-1543) Suggests a model that the Sun was the center of the universe. Argued that the motion of the Sun & planets could be equally described by a Sun centered (heliocentric) system.

15. Earth 1 Sun 1 2 3 4 5 6 6 Outer Planet 5 4 3 2 Fixed Stars Planet's apparent path around sky. Earth overtakes slow outer planet so the outer planet appears to slow down, move in reverse, and then move forward again with respect to the fixed stars. Retrograde Motion http://faculty.salisbury.edu/~jwhoward/astro108/html/GeoHelio.ppt#274,10,Slide 10

16. Tycho Brahe (1546-1601): the greatest of the pre-telescope observers in Europe. 20+ years measuring the positions of the Sun, Moon and planets with great accuracy.

17. Johannes Kepler (1609) Johannes Kepler was an assistant to Tycho Brahe. He used Brahe’s observations to study the orbit of Mars Discovered three laws of planetary motion: predict with accuracy the motions of the planets

18. Galileo (1564-1642) first scientist to use a telescope to observe the sky. He observed the phases of Venus and the moons of Jupiter. Both observations supported the heliocentric model.

19. Modern Universe Is the Sun the center of the Universe?

20. Final Question