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© 2005 Pearson Education Inc., publishing as Addison-Wesley The Planets Prof. Geoff Marcy The Nature of Scientific Theories Giants of Scientific Thinking.

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Presentation on theme: "© 2005 Pearson Education Inc., publishing as Addison-Wesley The Planets Prof. Geoff Marcy The Nature of Scientific Theories Giants of Scientific Thinking."— Presentation transcript:

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 Sept. 11

2 © 2005 Pearson Education Inc., publishing as Addison-Wesley Announcements Read Chapter 3 ! Homework Assignment: - Assignment Chapters 3: Due Fri at 6pm Get your ABCD cards ready.

3 Observing Project #1: Monitoring the Motion of Mars Chart the position of Mars in the night sky relative to Saturn and the star, Antares. Observe Mars, Saturn, and Antares in the evening sky three times (at least once per week), between now (Sept 9) and Sept 30. Draw a sketch each evening (or take a photo), showing the positions of Antares, Mars, and Saturn as dots. Record the time and date on the sketch. After you have made your three (or more) sketches, write one to two paragraphs explaining your observations of the position of Mars. Did it move? If so, why did it move the way it did? Due Thursday, October 2. Sept. 5, 2014

4 Tycho Brahe ( ) Best Observer of the position of Mars (including retrograde motion)! Danish King, Fredrick II, gave him the entire island of Hveen for observations. Even better charts of planets positions. Johannes Kepler wanted Brahe’s data, to explain Mars’s orbit. Another astronomer wanted Brahe’s data: Frank Tengnagel

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6 Tycho Brahe ( ) Body Exhumed in 2010

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8 © 2005 Pearson Education Inc., publishing as Addison-Wesley Johannes Kepler ( ) Greatest theorist of his day Imagined planets on “heavenly spheres”

9 © 2005 Pearson Education Inc., publishing as Addison- Wesley Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus. Assuming a circular orbit for Mars, Kepler could not match Brahe’s precise measurement of Mars’ orbit. A tiny difference of 8 arc minutes (0.13 o ) remained. So he abandoned “uniform” and “circular” motion.

10 © 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.

11 © 2005 Pearson Education Inc., publishing as Addison-Wesley Eccentricity of an Ellipse

12 © 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s 2nd Law A planet’s speed changes predictably: A line from the planet to the Sun sweeps out equal areas in equal intervals of time.

13 © 2005 Pearson Education Inc., publishing as Addison-Wesley

14 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

15 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

16 © 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

17 Calculate the orbital period of: Planet a (AU) Period (yrs) Mercury days = 0.25 yr Venus days = 0.59 yrs Earth Mars Jupiter Saturn Uranus Neptune Pluto

18 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…

19 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 ( )

20 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..

21 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.

22 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.

23 © 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!

24 © 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

25 © 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

26 © 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.

27 © 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.

28 © 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.

29 © 2005 Pearson Education Inc., publishing as Addison-Wesley

30 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

31 Horoscope: Sept. 11,

32 © 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 number thatChoose the horoscope number that best describes your day today best describes your day today numberWrite that number on your 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

33 Horoscope: Sept. 11,

34 © 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.

35 Horoscope: Sept. 11, Stand up if you chose #1 Stand up if you chose #2 Stand up if you chose #3 Stand up if you chose #4 Stand up if you chose #5 Stand up if you chose #6 Stand up if you chose #7 Stand up if you chose #8 Stand up if you chose #9 Stand up if you chose #10 Stand up if you chose #11 Stand up if you chose #12

36 © 2005 Pearson Education Inc., publishing as Addison-Wesley Theory: Astrology predicts your day 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 own horoscope. Only 1/10 of you recognized your horoscope! Astrology, as a theory, didn’t match real world.

37 © 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?

38 © 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.


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