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 497,000 MPH Speed of the Milky Way 89,000 MPH Speed of “Local Group” 1,367,000 MPH Our speed relative to the universe 65,000 MPH http://en.wikipedia.org/wiki/Hubble_sequence
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 0.017 Avg. orbital speed 66,622 MPH Rotational speed (equator) 1040 MPH Axial tilt 23.4° 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. 30-40 of Chapter 2 in the textbook for Thursday 01/24