Chapter 4 The Origin Of Modern Astronomy Slide 14 Slide 15 14 15 Is Change Good or Bad? Do you like Homer to look like Homer or with hair? Does it bother you when your schedule is changed? Is it okay to change the spelling of certain words? Gray vs Grey Colour vs Color Flavour vs Flavor Humour vs Humor Labour vs Labor Is okay to change your phone? From ios to Android From Android to ios Would it bother you if the sun rose in the west and set in the east? 1500 1550 1600 1650 1700 1750 Copernicus Columbus Tycho Brae Galileo Kepler Black Plague Newton Slide 16 Would it be okay if a day lasted 30 hours and not 24 hours? Slide 17 16 17
Assumptions (For this section, the following assumptions will be used.) Uniform Circular Motion Geocentric Universe Heavens Perfect Ancient Greek Astronomers Aristotle (384 322 B.C.), major authority of philosophy until the late middle ages: Universe can be divided in 2 parts: 1. Imperfect, changeable Earth, 2. Perfect Heavens (described by spheres) Slide 18 Slide 19 18 19 How Ancient Astronomy arrived at these conclusions Fundamental argument for the geocentric universe: Slide 20 Motion of Earth should result in an observable parallax, which was not seen. 20 21 Left arm extended, thumb up Right hand covering right eye Cover my face with your thumb Move your right hand from your right eye and cover your left eye
Ancient Greek Astronomy Models were generally wrong because they were based on wrong first principles, believed to be obvious and not questioned: (I think therefore it is true.) Shorter Distance Parallax Longer Distance Slide 22 1. Geocentric Universe: Earth at the Center of the Universe. 2. Perfect Heavens : Motions of all celestial bodies described by motions involving objects of perfect shape, i.e., spheres or circles. 22 23 What we know today Slide 23 Stellar Parallax (what we see today) Aristotle s Universe What we know today 24 25 Slide 25 p. 44
Aristotle s Universe Slide 26 26 Aristotle s Universe Slide 27 27 Assumptions Not Changed Uniform Circular Motion Geocentric Universe Heavens Perfect Slide 28 28 Slide 29 29
The What Scientific we now Method use Observations (forming the question) Idea / Thought When a horse gallops, what is the minimum number of feet touching the ground at any one time? The Scientific Method Observations (forming the question) Idea / Thought When a horse gallops, what is the minimum number of feet touching the ground at any one time? Hypothesis (The guess) Explain the observation, mathematically if possible When the horse gallops, one foot is always touching the ground. Slide 30 30 31 Slide 31 The Scientific Method Observations (forming the question) Idea / Thought When a horse gallops, what is the minimum number of feet touching the ground at any one time? Hypothesis (The guess) Explain the observation, mathematically if possible When When the the horse horse gallops, gallops, all one feet foot come is always off the touching ground. the ground. Experimentation (The Data) By independent analysis to confirm hypothesis Take pictures and analyze the pictures The Scientific Method Observations (forming the question) Idea / Thought When a horse gallops, what is the minimum number of feet touching the ground at any one time? Hypothesis (The guess) Explain the observation, mathematically if possible When the horse gallops, all feet come off the ground. Experimentation (The Data) By independent analysis to confirm hypothesis Take pictures and analyze the pictures Theory / Law (accepted truth) Proven over time Verify by analyzing lots of horses over a sufficiency long period of time. Slide 32 32 33 Slide 33
The Scientific Method Is Science always correct? No Does Science correct it s self when it knows it is wrong? Yes Do people believe in the finding of Science? Not always, but the good news is that people die and the next generation will typically accept the findings of Science. Claudius Ptolemy 87-150 AD Astronomer Mathematician Geographer Explained the Retrograde Motion of the Planets Used Epicycles and Deferents to describe motion. Slide 34 34 35 Slide 35 Retrograde Movie Retrograde Movie Slide 36 36 37 Slide 37
Issues of Ancient Astronomy Retrograde Motion The retrograde (westward) motion of the planets The solution : Epicycles! Slide 38 Slide 39 38 39 Slide 40 Slide 41 40 41
p. 45 Slide 42 Slide 43 42 43 Slide 44 Slide 45 44 45
Introduced by Claudius Ptolemy Ptolemy (ca. A.D. 140) The Ptolemaic system was considered the standard model of the universe until the Copernican Revolution. Slide 46 Slide 47 46 47 The Copernican Revolution Assumptions Modified but not Changed Uniform Circular Motion Geocentric Universe Heavens Perfect Nicolaus Copernicus (1473 1543): Slide 48 48 Slide 49 49 heliocentric universe (sun in the center)
Slide 50 Slide 51 50 51 Copernicus new (and correct) explanation for retrograde motion of the planets: Retrograde (westward) motion of a planet occurs when Earth passes the planet. 52 53 Slide 53 This made Ptolemy s epicycles unnecessary.
Fig. 4-4a, p. 49 Slide 54 Slide 55 54 55 Fig. 4-4b, p. 49 Assumptions Tycho Brahe (1546 1601) Uniform Circular Motion Heliocentric Universe Heavens Perfect Slide 56 Slide 57 56 57 Use of high-precision instruments for precise astronomical observations, meticulously reported in tables. Later used by Kepler to develop laws of planetary motion.
Slide 59 Slide 60 59 60 A Quadrant designed by Brahe Used to precisely measure an object s angular distance above the horizon Slide 61 61 62 Slide 62
Slide 63 Slide 64 63 64 Tycho Brahe Assumptions It was long been thought that Tycho Brahe died of a complication to his bladder, when he did not let his urine from politeness at a dinner in Prage 1601, eleven days before his death. However, more recent studies started 1996 from opening the grave of Tycho Brahe and analysing his hair, have showed that it is very likely that Tycho Brahe in fact died from Mercury poisoning. Slide 65 65 Uniform Circular Motion Geocentric Universe Heavens Perfect Slide 66 66
Johannes Kepler (1571 1630) Used the precise observational tables of Tycho Brahe to study planetary motion mathematically. Found a consistent description by abandoning both: Johannes Kepler Slide 67 1. Circular motion and 2. Uniform motion. Planets move around the sun on elliptical paths, with non-uniform velocities. 67 68 Slide 68 Kepler s Laws of Planetary Motion Ellipse 1. The orbits of the planets are ellipses with the sun at one focus. c Eccentricity e = c/a Slide 69 69 70 Slide 70
Kepler s Laws of Planetary Motion 2. A line from a planet to the sun sweeps over equal areas in equal intervals of time. Exaggerated Eccentricity of Earth s Orbit Slide 71 71 72 Eccentricities of Ellipses 1) 2) 3) e = 0.02 e = 0.1 e = 0.2 Eccentricities of planetary orbits Orbits of planets are virtually indistinguishable from circles: Earth: e = 0.0167 Most extreme example: Pluto: e = 0.248 4) 5) e = 0.4 e = 0.6 Slide 73 Slide 74 73 74 But their centers may be significantly offset from the sun.
Kepler s Laws of Planetary Motion 3. A planet s orbital period (P) squared is proportional to its average distance from the sun (a) cubed: The Motion of the Planets The planets are orbiting the sun almost exactly in the plane of the ecliptic. Venus P y2 = a AU 3 Mercury (P y = period in years; a AU = distance in AU) Slide 75 Slide 76 75 76 Kepler s Laws 1. The planets move in ellipses with the sun at one focus. 2. The planet s radius vector sweeps out equal area per equal amount of time. 3. P 2 = D 3 Slide 77 Table 4-1, p. 55 Slide 78 77 78
Galileo Galilei (1594 1642) Assumptions Introduced the modern view of science: Transition from a faith-based science to an observation-based science. Finally will change Greatly improved on the newly invented telescope technology. (But Galileo did NOT invent the telescope!) Heavens Perfect Slide 79 Slide 80 79 Was the first to meticulously report telescope observations of the sky to support the Copernican model of the universe. 80 Major discoveries of Galileo: Galileo s Telescope Slide 81 81 Moons of Jupiter (4 Galilean moons) Slide 82 82
Major discoveries of Galileo: The mountains on the moon Major discoveries of Galileo (II): Rings of Saturn (What he really saw) Slide 83 Slide 84 83 84 sunspots (proving that the sun is not perfect!) Major discoveries of Galileo (III): Phases of Venus (including full Venus ), proving that Venus orbits the sun, not Earth! Major discoveries of Galileo (III): Phases of Venus (including full Venus ), proving that Venus orbits the sun, not Earth! Slide 85 85 86 Slide 86
Galileo was ordered to stand trial on suspicion of heresy in 1633. The sentence of the Inquisition was in three essential parts: 1.Galileo was required to recant his heliocentric ideas. 2.He was ordered imprisoned; the sentence was later commuted to house arrest. 3.His offending Dialogue was banned and publication of any of his works was forbidden. Slide 87 Slide 88 87 88 Heaven The Church s Understanding Until October 31, 1992 Galileo s Inventions Slide 90 90 Hell Slide 91 91 The Pump Hydrostatic Balance Pendulum Clock The Sector The Thermometer
Conclusion Slide 92 92 93 Slide 93 Fig. 4-16, p. 60 Isaac Newton (1643-1727) Newton s Laws Slide 94 Building on the results of Galileo and Kepler Adding physics interpretations to the mathematical descriptions of astronomy by Copernicus, Galileo and Kepler Major achievements: 1. Invented calculus as a necessary tool to solve mathematical problems related to motion 2. Discovered the three laws of motion 3. Discovered the universal law of mutual gravitation 94 95 Slide 95 1. A body in motion will stay in motion and a body at rest will stay at rest unless acted upon by an external force. 2. F=ma 3. Equal and opposing forces
Newton s First Law Newton s Laws 1. A body in motion will stay in motion and a body at rest will stay at rest unless acted upon by an external force. 2. F=ma 3. Equal and opposing forces Slide 96 Slide 97 96 97 Newton s Second Law Newton s Laws F=ma 1. A body in motion will stay in motion and a body at rest will stay at rest unless acted upon by an external force. 2. F=ma 3. Equal and opposing forces Slide 98 Slide 99 98 99
Slide 100 Slide 101 100 101 Slide 103 102 103 Table 4-2, p. 62
Newton s Laws 1. A body in motion will stay in motion and a body at rest will stay at rest unless acted upon by an external force. 2. F=ma 3. Equal and opposing forces Slide 104 Slide 105 p. 63 104 105 Slide 106 The Universal Law of Gravity Any two bodies are attracting each other through gravitation, with a force proportional to the product of their masses and inversely proportional to the square of their distance: F = - G Mm r 2 (G is the gravitational constant.) Slide 107 Understanding Orbital Motion The universal law of gravity allows us to understand orbital motion of planets and moons: Example: Earth and moon attract each other through gravitation. Since Earth is much more massive than the moon, the moon s effect on Earth is small. Earth s gravitational force constantly accelerates the moon towards Earth. This acceleration is constantly changing the moon s direction of motion, holding it on its almost circular orbit. v v Moon F Earth v 106 107
Orbital Motion (II) In order to stay on a closed orbit, an object has to be within a certain range of velocities: Too slow : Object falls back down to Earth Too fast : Object escapes the Earth s gravity Slide 108 Slide 109 108 109 Newton and his telescope Orbital Motion (III): Geosynchronous Orbits Newton developed the reflecting telescope. ~1880, eye replaced with the camera ~1950, spectral analysis of stars Slide 110 110 111 Slide 111
How to Study Aristotle Uniform circular motion, geocentric universe, heavens perfect Ptolemy Uniform circular motion with epicycles, geocentric universe, heavens perfect Copernicus Uniform circular motion with epicycles, heliocentric universe, heavens perfect Tyco 20 years on the island of Hven recording the positions of the stars Kepler Elliptical motion, heliocentric universe, three laws of planetary motion Galileo Proved that the heavens were not perfect Newton Three laws of motion, explained why the moon revolved around the earth, universal law of gravitation For the Final Study all of the tests x 3 If time left over Study the quizzes Study your notes Study the book Understand the stuff For the Test Study all of the quizzes since the previous test x 3 If time left over Study your notes Study the book Understand the stuff For the Quiz Study your notes Study the book Slide 112 Slide 113 112 113 Slide 114 114