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Astronomy 104: Stellar Astronomy Lecture 4: Science and our Understanding of the Universe (Continued) Spring Semester 2013 Dr. Matt Craig Monday, January 28, 13 1 For next time: • Bring Lecture-Tutorials for Introductory Astronomy. • Chapter 3, Sections 2-4 • Reminder: • Do your moodle assignments, due EVERY Friday. 2 Monday, January 28, 13 2 Objectives •Describe Galileo’s observations (3-3). •Explain why Galileo’s observation of the phases of Venus demonstrated that the geocentric model was incorrect (and do the same for his observation that Jupiter has moons) (3-3) •Describe Copernicus’ heliocentric model (3-2) •Explain why Copernicus’ heliocentric model wasn’t accepted immediately (3-2) •Describe Tycho’s contribution to the discovery of the correct description of the Solar System. (3-4) 3 Monday, January 28, 13 3 Explaining Motions of Planets: two broad ideas Geocentric: Earth at center center Heliocentric: Sun at Monday, January 28, 13 4 Ptolemy’s Geocentric Theory (Animation) Mars’ Orbit in Geocentric Theory (simplified) • Says planets moved on circular paths nested on circular orbits to describe the motions of the planets. O = Earth P = Mars Yellow Dot = Sun • Complicated... but accurate enough to match available observations.. http://people.scs.fsu.edu/~dduke/models Monday, January 28, 13 5 5 Copernicus' Heliocentric Model (Animation) Mars’ Orbit in Heliocentric Model (Simplified) • Just have a few circles centered on the Sun. • Unfortunately... O = Earth P = Mars Yellow Dot = Sun doesn’t simplify calculations much. • As accurate as Greek Geocentric Theory, BUT NOT MORE ACCURATE. http://people.scs.fsu.edu/~dduke/models Monday, January 28, 13 6 6 So why didn’t Copernicus’ Model take off... • Computations almost as tedious... (no real savings) • Copernicus’ model wasn’t any better or worse than a Geocentric theory at predicting positions of planets, as far as observers then could tell. • KEY POINT: What was needed were predictions that would distinguish this model from the Geocentric Theory. We're stuck, since no test can distinguish between the two models/theories!!! 7 Monday, January 28, 13 7 Direct Comparison: Motion of Venus Heliocentric (Sun-Centered) Geocentric (Earth-Centered) Notice in both cases Venus (P) as seen from Earth (O) never appears to be far from Sun (Yellow dot). 8 Monday, January 28, 13 8 Turning a Heliocentric Model into a Theory • Galileo Galilei uses a telescope to look at the sky (he did not invent it). • Laid the groundwork for a better understanding of physics • He looked at Venus and noticed its phases... Galileo Galilei (1564 - 1642) 9 Monday, January 28, 13 9 Lecture Tutorial • Please get together with your neighbor and work on the "Testing a Scientific Theory, Part 2". • Rules: • You must work in groups of at least 2 and no more than 4. • You must come to an agreement on all answers BEFORE writing them down. 10 Monday, January 28, 13 10 OK.... And???? • Do you want to know what Galileo actually saw for the phases of Venus? 11 Monday, January 28, 13 11 Observed phases of Venus Image credit: Chris Proctor, Torbay Astronomical Society http://www.halien.net/TAS/index.htm Monday, January 28, 13 12 12 Galileo’s Observations The Moons of Jupiter The Sky is Full of Faint Stars Monday, January 28, 13 Mountains on the Moon Sunspots on June 23 1612. The Phases of Venus 13 Galileo’s observations 1.Phases of Venus 2.Moons of Jupiter • Observed four moons of Jupiter • Like a “mini-solar system” 3.Discovered that sun rotates about once per month by observing sunspots 4.Moon has mountains and valleys, like Earth • Suggests other bodies in solar system are like Earth 5.Found that the Milky Way is composed of many, many individual stars 14 Monday, January 28, 13 14 Let’s try those clickers! •Turn it on. •If your clicker doesn't connect, you may need to configure your clicker (only need to do this once) •Press and hold on/off button for two seconds. •Press A, then A. •Register your iClickers following the instructions on the back of the remote. If you forget to do this before the end of the semester, you will not get credit for your participation in this class. Monday, January 28, 13 15 McQuestion • Which of the following statements would you say is most correct about Galileo's observations. (A)Galileo proved the heliocentric model of the solar system is correct. (B)Galileo proved the geocentric model of the solar system is incorrect. (C)Both (A) and (B). (D)Neither (A) or (B) since you can't "prove" the truth of a theory in science! 16 Monday, January 28, 13 16 "Not right" doesn’t necessarily mean "completely wrong" • Copernicus’ heliocentric (sun-centered) model was no more accurate than the Greek geocentric (Earth-centered) model • By the time Galileo whipped out his telescope, observations showed both models inaccurately predicted planetary positions. • Do observations contradicting predictions of your model mean you have to toss out the entire model? 17 Monday, January 28, 13 17 Aside: a “hybrid” model Earth 18 Monday, January 28, 13 18 Tycho Brahe: The Bad Boy of Astronomy • Made very accurate observations • Didn’t think heliocentric model was right since no parallax of stars observed. Tycho Brahe (1546-1601 CE) Monday, January 28, 13 19 19 For next time: • Bring Lecture-Tutorials for Introductory Astronomy. • Chapter 3, Sections 2-4 20 Monday, January 28, 13 20