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

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

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.

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

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

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

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

Plato, Aristotle, Ptolemy: The Heavenly Spheres

The Celestial Sphere

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)

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.

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

The heliocentric system and retrograde motion

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)

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