1. © 2005 Pearson Education Inc., publishing as Addison-Wesley The Planets Prof. Geoff Marcy The Nature of Scientific Theories Giants of Scientific Thinking Astrology Lecture 4b 2012 Sept. 6

2. © 2005 Pearson Education Inc., publishing as Addison-Wesley Announcements Read Chapter 4 ! Homework: MasteringAstronomy: Chapt 4. Past Homework Assignments: - Assignment Chapters 1&2: Due tomorrow 6pm - Assignment Chapters 3: Due tomorrow 6pm - Question: Raise your hand if you can’t get into MasteringAstronomy. -Observation Project: Due Right now! Tue, Wed, Thu 12-1: Disc. Sections Not full!

3. To purchase stand-alone access to MasteringAstronomy if you didn’t buy a book or access code in the bookstore. You can buy both the eBook and MasteringAstronomy: $85.

4. © 2005 Pearson Education Inc., publishing as Addison-Wesley Scientific Thinking It is a natural part of human curiosity: Search for understanding and truths that explain many facts. We draw conclusions based on our experiences. Progress is made through “trial and error.” Hypothesize. Then test your hypothesis. Eating pasta makes me get fat...

5. © 2005 Pearson Education Inc., publishing as Addison-Wesley Nicolaus Copernicus (1473-1543) He thought Polemy’s model was contrived Yet he believed in circular motion De Revolutionibus Orbium Coelestium

6. © 2005 Pearson Education Inc., publishing as Addison-Wesley Copernicus’ Heliocentric Model Sun is at center Earth orbits like any other planet Inferior planet orbits are smaller Retrograde motion occurs when we “lap” Mars & the other superior planets

7. © 2005 Pearson Education Inc., publishing as Addison-Wesley Johannes Kepler (1571-1630) Greatest theorist of his day Imagined planets on “heavenly spheres”

8. © 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s Laws 1. Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus.

9. © 2005 Pearson Education Inc., publishing as Addison-Wesley Eccentricity of an Ellipse

10. © 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s 2nd Law A planet moves along its orbit with a speed that changes in such a way that a line from the planet to the Sun sweeps out equal areas in equal intervals of time.

11. © 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s 3rd Law The cube of a planet’s average distance from the Sun is equal to the square of its orbital period. (Use units of years and AUs.) a 3 = P 2

12. © 2005 Pearson Education Inc., publishing as Addison-Wesley Galileo Galilei (1564-1642) First man to point a telescope at the sky wanted to connect physics on earth with the heavens Dialogue Concerning the Two Chief World Systems [written in Italian] This book got him in trouble with the Church!

13. © 2005 Pearson Education Inc., publishing as Addison-Wesley Galileo’s Observations Galileo discovered that Jupiter had four moons of its own. Jupiter was the center of its own system. Heavenly bodies existed which did not orbit the earth.

14. Tycho Brahe (1546-1601) Greatest observer of his day Born into the most prestigious families in Denmark King Fredrick II offered him the entire island of Hveen for observations Best charts of planets positions Johannes Kepler Kepler’s task: explain Mars’s orbit

15. Tycho Brahe (1546-1601) Tycho Brahe (1546-1601) Greatest observer of his day Born into the most prestigious families in Denmark King Fredrick II offered him the entire island of Hveen for observations Best charts of planets positions Two observers: Johannes Kepler & Frank Tengnagel Kepler’s task: explain Mars’s orbit

16. Tycho Brahe (1546-1601) Greatest observer of his day Born into the most prestigious families in Denmark King Fredrick II offered him the entire island of Hveen for observations Best charts of planets positions Two observers: Johannes Kepler & Frank Tengnagel Kepler’s task: explain Mars’s orbit

17. Tycho Brahe (1546-1601) Exhumed in 2010

18. © 2005 Pearson Education Inc., publishing as Addison- Wesley Kepler’s 1st Laws Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus. Kepler could not match Brahe’s precise measurement of Mars’ orbit. A tiny different of 8 arc minutes (0.13 o ) remained. Then he abandoned the idea of “uniform” and “circular” motion.

19. © 2005 Pearson Education Inc., publishing as Addison-Wesley

20. Kepler’s 3rd Law The cube of a planet’s average distance from the Sun is equal to the square of its orbital period. Orbital period: P (measure in years) planet’s average distance: a (measure in AU) P 2 = a 3 a More precisely: a is the semi major axis

21. Question: An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun? A.4 years B.8 years C.16 years D.64 years Hint: Remember that P 2 ~ a 3

22. © 2005 Pearson Education Inc., publishing as Addison- Wesley Question: An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun? A.4 years B.8 years C.16 years D.64 years We need to find P so that P 2 = a 3. Since a = 4, a 3 = 4 3 = 64 Therefore P= 8, P 2 = 8 2 = 64

23. Calculate the orbital period of: Planet a (AU) Period (yrs) Mercury 0.4 92 days = 0.25 yr Venus 0.7 214 days = 0.59 yrs Earth 1.0 1.0 Mars 1.5 1.8 Jupiter 5.0 11.2 Saturn 10 32 Uranus 20 89 Neptune 30 164 Pluto 50 354

24. WHY do planets move on elliptical orbits? Astronomers Kepler, Halley, Wren, and Hooke proposed an inverse square law of gravity: Force of gravity ~ 1 / distance 2 In 1684, Sir Christopher Wren issued a small prize (40 shillings) for the first person who could prove that Kepler’s first law follows from an the gravity law above. In August of 1684, Halley met Isaac Newton in Cambridge…

25. Realized the same physical laws that operate on Earth also operate in the heavens  one universe Discovered laws of motion and gravity Much more: experiments with light; first reflecting telescope (using mirrors rather than lenses) Invented calculus in parallel to Friedrich Leibnitz in Germany How did Newton change our view of the Universe? Sir Isaac Newton (1642-1727)

26. 1. What determines the strength of gravity? The Universal Law of Gravitation 1.Every mass attracts every other mass. 2.Attraction is directly proportional to the product of their masses. 3.Attraction is inversely proportional to the square of the distance between their centers..

27. Is the force the Earth exerts on you larger, smaller, or the same as the force you exert on it? Question: Is the force the Earth exerts on you larger, smaller, or the same as the force you exert on it? A.Earth exerts a larger force on you. B.I exert a larger force on Earth. C.Earth and I exert equal and opposite forces on each other.

28. Is the force the Earth exerts on you larger, smaller, or the same as the force you exert on it? Question: Is the force the Earth exerts on you larger, smaller, or the same as the force you exert on it? A.Earth exerts a larger force on you. B.I exert a larger force on Earth. C.Earth and I exert equal and opposite forces on each other.

29. © 2005 Pearson Education Inc., publishing as Addison-Wesley Galileo’s observation of the phases of Venus was the final evidence which buried the geocentric model. GeocentricHeliocentric No gibbous or full phases!All phases are seen! Galileo observed all phases!

30. © 2005 Pearson Education Inc., publishing as Addison-Wesley The Scientific Method 1Question 2Hypothesis –a tentative explanation 3Prediction 4Test 5Result –confirm, reject, or modify should be the same no matter who conducts the test

31. © 2005 Pearson Education Inc., publishing as Addison-Wesley Science seeks explanations for observed phenomena that rely on natural causes. Science progresses through the construction and testing of models of nature that explain the observations as simply as possible. !Occam’s Razor A scientific model must make testable predictions that could force us to revise or abandon the model. Hallmarks of Good Science -- a concept or set of ideas (a “model”) that survives repeated testing Theory

32. © 2005 Pearson Education Inc., publishing as Addison-Wesley Bad Scientific Practice pseudoscience – beliefs that masquerade as science, but do not change as new evidence comes in that contradicts those beliefs. nonscience – establishes “truths” through belief and faith. Tests are not done.

33. © 2005 Pearson Education Inc., publishing as Addison-Wesley Astrology Claims the positions of the Sun, Moon, & planets determines each person’s personality and each person’s future.

34. © 2005 Pearson Education Inc., publishing as Addison-Wesley Astrology Theory: The positions of the planets, sun, and moon at the time of your birth determine your personality and your future every day.

35. © 2005 Pearson Education Inc., publishing as Addison-Wesley

36. Signs of the Zodiac AQUARIUS January 19-February 17 PISCES February 18-March 19 ARIES March 20-April 18 TAURUS April 19-May 19 GEMINI May 20-June 19 CANCER June 20-July 21 LEO July 22-August 21 VIRGO August 22-September 21 LIBRA September 22-October 22 SCORPIO October 23-November 20 SAGITTARIUS November 21-December 20 CAPRICORN December 21-January 18

37. Horoscope Sept. 6, 2012 1 2 3 4 5 6 7 8 9 10 11 12

38. © 2005 Pearson Education Inc., publishing as Addison-Wesley Test of Astrology Write your “sign” of the zodiac on one sheet of paper. Choose the horoscope thatChoose the horoscope that best describes your day today best describes your day today Write the NUMBER of that paragraph 1 - 12 on that paper. Signs of the Zodiac AQUARIUS January 19-February 17 PISCES February 18-March 19 ARIES March 20-April 18 TAURUS April 19-May 19 GEMINI May 20-June 19 CANCER June 20-July 21 LEO July 22-August 21 VIRGO August 22-September 21 LIBRA September 22-October 22 SCORPIO October 23-November 20 SAGITTARIUS November 21-December 20 CAPRICORN December 21-January 18

39. Horoscope Sept. 6, 2012 1 2 3 4 5 6 7 8 9 10 11 12

40. © 2005 Pearson Education Inc., publishing as Addison-Wesley Existing Astrology Theory: You can predict your future. If Theory is True: If Theory is True: You will recognize your horoscope: It pertains to you! You will recognize your horoscope: It pertains to you! If Theory is not true. If Theory is not true. You will choose a random horoscope.

41. Horoscope Sept. 6, 2012 1 2 3 4 5 6 7 8 9 10 11 12

42. Horoscope Sept. 6, 2012 1 2 3 4 5 6 7 8 9 10 11 12 Chose #1? Stand up !

43. © 2005 Pearson Education Inc., publishing as Addison-Wesley Existing Theory: Astrology works The horoscope for your sign of the zodiac allows you to predict your future. If Theory is True: If Theory is True: People will recognize their horoscope. People will recognize their horoscope. If Theory is not true. If Theory is not true. People will not recognize their horoscope.

44. © 2005 Pearson Education Inc., publishing as Addison-Wesley Astrology: What is the Mechanism that makes it work? What force makes the planets determine your entire life? What is the “energy” that makes planets control your life? What force exerted by planets acts on you at the moment of birth to determine the rest of your life?

45. © 2005 Pearson Education Inc., publishing as Addison-Wesley Astrology: Invent your own Why do only planets and moons affect your life? Other objects exert great gravitational forces on you, such as nearby buildings, aircraft, mountains. Quiz: Invent your own “astrology” based on the positions of some other objects around you.