1. Homework, HW#1 due today Announcements Questions? Tuesday, January 22
Spring 2008

2. The Scientific Method
Scenario: Your phone hasn’t rung in several days, but your friend says s/he tried calling you.
Task: Come up with a few different hypotheses that would explain why your phone hasn’t rung and how you would test them.

3. Chapter 2: The Ordered Universe
Newton’s laws of motion and gravity predict the behavior of objects on Earth and in space.

4. Our (place in the) Galaxy
near infrared map of the Milky Way Galaxy
Estimated Diameter of “Observable Universe” = 78 billion light-years
1 light-year ≈ 5.9 trillion miles
NGC 7331
(Milky Way’s galaxy twin)
Rotational speed of solar system ,000 MPH
Speed of the Milky Way ,000 MPH
Speed of “Local Group” ,367,000 MPH
Our speed relative to the universe 65,000 MPH

5. Our (place in the) Solar System
orbits of the inner planets
orbits of the planets
Earth orbital characteristics:
Avg. Distance from Sun 93 million miles
Length of orbital path 574 million miles
Orbital eccentricity
Avg. orbital speed 66,622 MPH
Rotational speed (equator) MPH
Axial tilt °
relative sizes of the planets

6. Observing patterns in nature – application of knowledge
Stonehenge, ~2800 B.C.
= 500 people
50,000 kg
100 kg / person

7. Plato, Aristotle, Ptolemy: The Heavenly Spheres

8. The Celestial Sphere

9. Ptolemy and the explanation of retrograde motion
Claudius Ptolemaeus (90 – 168 AD)
Retrograde motion: the apparent backward motion of a planet relative to the fixed stars.
retrograde motion (animation)

10. Ptolemy and the explanation of retrograde motion
retrograde motion predicted by epicycles (animation)
Ptolemy introduces planetary epicycles: the epicycle is a sphere embedded in the planet’s celestial sphere. Together, these spheres move the planet.

11. Copernicus and the heliocentric system
All planets orbit the sun in perfect circles.
Earth rotates on an axis through its center.
Easier to explain retrograde motion.
Epicycles still utilized.
Does not provide completely accurate predictions
Nicolaus Copernicus (1473 – 1543)
Copernican
heliocentric theory

12. The heliocentric system and retrograde motion

13. Tycho Brahe’s view on planetary motion
The last great naked-eye astronomer (telescopes did not exist while he was alive)
Constructed a large quadrant to make highly accurate measurements of the positions of the planets and stars
Tycho Brahe (1546 – 1601)

14. Chapter 1 quiz in class on Thursday 01/24
Read pp of Chapter 2 in the textbook for Thursday 01/24