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Objectives – Same as Last Lecture Describe the geocentric and the heliocentric models of the solar system. The word planet derives from the Greek "planetes" which means wanderer. Why were the planets called wanderers? Explain Aristotle’s main argument against the heliocentric model. What was Aristotle’s other (and weaker) argument against the heliocentric model? Who gave the first evidence in favor of the heliocentric model? What was the evidence? Who added the mathematical calculations to the geocentric model? When a planet undergoes retrograde motion, how does it look? How did the geocentric model explain retrograde motion? How did the heliocentric model explain retrograde motion? What did Brahe contribute to the heliocentric vs. geocentric debate? Define perihelion and aphelion. Considering Kepler's three laws of planetary motion (you do not have to memorize them): What shape orbit does a planet have? When a satellite orbits the Earth, does it move faster at perigee or at apogee? When a comet orbits the Sun, does it orbit faster at perihelion or at aphelion? What is meant by the period of a planet? In our solar system, what planet has the longest period? The shortest? Which planet orbits with the highest speed? Slowest? What did Galileo notice about the Moon, the Sun, Jupiter, and Venus? What did he conclude from these observations? How did the church/state react? Why does Venus exhibit phases but Mars does not? (Hint: Draw the Sun as well as Venus, Earth and Mars in their orbits. Shade in Venus and Mars. What do they look like from Earth’s view?) State Newton's Universal Law of Gravity. If the mass of one of two objects increases, what happens to the gravitational force between the objects? If the distance between the two increases, what happens to the force? How can you tell if a process is science? (See earlier lecture on the hallmarks of science.) When science uses the term “theory” such as the “Theory of Evolution”, is that a weak or a strong statement? What backs up any theory in science? Copernican Revolution ~1500 to ~1700 People Who Contributed* Copernicus (~1500) Brahe (~1570) Kepler (~1600) Galileo (~1600) Newton (~1670) Copernican Revolution Copernicus (~1500) Resurrected heliocentric model* First suggested by Aristarchus* Copernican Revolution Is solar system geocentric or heliocentric?* Copernican Revolution Both models have: Circular orbits (heavenly perfection) Uniform motion (heavens cannot change) Copernican Revolution Both models explain observations… Sun, Moon, Planets Rise in east, Set in west Copernican Revolution Both models explain observations… Retrograde motion of planets Copernican Revolution Retrograde motion – Geocentric Planets ride on epicycles Sometimes appear to move backwards Copernican Revolution Retrograde motion – Heliocentric One planet overtakes another planet. Slower planet appears to move backwards. Copernican Revolution Copernicus (~1500) Brahe (~1570) Kepler (~1600) Galileo (~1600) Newton (~1670) Copernican Revolution Brahe (~1570) Built excellent instruments.* Collected 20+ years of data from observations.* Measured position of Mars very accurately.* Stayed with geocentric model.* Saw a supernova! (the sky changed) Copernican Revolution Copernicus (~1500) Brahe (~1570) Kepler (~1600) Galileo (~1600) Newton (~1670) Copernican Revolution Kepler (~1600) Derived (from Brahe’s data) Three mathematical laws of planetary motion. Copernican Revolution Kepler’s First Law 1. Planets have elliptical orbits around the Sun* < aphelion perihelion > Copernican Revolution Kepler’s Second Law 2. The radius vector sweeps out equal areas in equal times. < > Thirty days Thirty days Radius vector > Copernican Revolution Kepler’s Second Law means that… A planet changes speed*; faster at perihelion, slower at aphelion Perihelion (faster) Aphelion (slower) Copernican Revolution Definition needed for Kepler’s Third Law Period = Time to complete one cycle Ex: Earth’s period of rotation =? Ex: Earth’s period of revolution = ? Copernican Revolution Kepler’s Third Law 3. Period2 is proportional to (Radius of orbit)3 • Sometimes written as P2 α r3 • Bigger orbit radius means longer to revolve • More distant planet takes more time to revolve.* • More distant planet moves slower.* Copernican Revolution Kepler’s 3 Laws 1. 2. Planets have elliptical orbits around the Sun* The radius vector sweeps out equal areas in equal times. • 3. A planet changes speed* Period2 is proportional to (Radius of orbit)3 • More distant planet takes more time to revolve.* Copernican Revolution Kepler’s Laws Also applies to objects in orbit around a central mass •Satellites around Earth •Star around a black hole •Planets around other stars •Two stars orbiting each other Copernican Revolution Copernicus (~1500) Brahe (~1570) Kepler (~1600) Galileo (~1600) Newton (~1670) Copernican Revolution Meanwhile… Out in the streets… Galileo (~1600) Developed and used the telescope Copernican Revolution Galileo observed… 1. Moon craters* Heavens are not perfect* !!!Heavens are Earth-like!!!* Copernican Revolution Cigoli – 1622 El Greco < 1600 Painted imperfect cratered Moon Painted imperfect heavens Copernican Revolution Art and ideas flourished* Frontpiece of G.B. Riccioli's Almagestum Novum, 1651. • • Important astronomy reference book Image includes • • • Models (Copernicus, Riccioli, Ptolemy) Riccioli’s model has Jupiter and Saturn centered on Earth Solar scope. Top of the Riccioli’s famous image (from previous slide) • Planets around the Sun Galileo observes… 1. Moon Craters* Heaven is not perfect!!* 2. Sunspots* Sun Rotates Copernican Revolution 3. Galileo observes… 4 Moons of Jupiter* Earth is not the ONLY center of motion in the heavens Copernican Revolution 3. Galileo observes… 4 Moons of Jupiter* AND Take that, Aristotle! Hey, Aristotle. Earth can move and pull the Moon along. Copernican Revolution 4. Galileo Observes Phases of Venus* • Geocentric model predicts: • Crescent phase only and little size change • Heliocentric predicts: • All phases AND • Gibbous is small, while crescent is large Play Venus phases video http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/PhasesofVenus.htm Copernican Revolution 4. Galileo Observes Phases of Venus* Copernican Revolution http://astronomy.nmsu.edu/geas/lectures/lecture11/slide02.html Copernican Revolution Galileo Observed* 1. Imperfect heavens, like Earth* • Moon craters* 2. Sunspots* 3. Jupiter’s moons* 4. Phases of Venus* Copernican Revolution Copernicus (~1500) Brahe (~1570) Kepler (~1600) Galileo (~1600) Newton (~1670) Copernican Revolution Newton (~1700) HOW planets orbit (and objects move) Same laws apply to terrestrial (Earth) objects and celestial objects* o called the Newtonian synthesis o Means Earth and heavens are alike* Copernican Revolution Newton (~1700) HOW planets orbit (and objects move) Newton’s Cannon Demo http://spaceplace.nasa.gov/how-orbits-work/en/ • Objects in orbit are continuously falling* • Floating in space is really falling (not due to zero gravity) Copernican Revolution Newton (~1700) Three Laws of Motion (Read but not on test) And The Universal Law of Gravity* Copernican Revolution Newton - Universal Gravity* Every mass exerts a force on every other mass. Note the UNIVERSAL statement. F m1 F m2 Copernican Revolution Newton - Universal Gravity F m1 F m2 Gravity always attracts* Bigger mass means bigger force* Bigger separation means smaller force* Copernican Revolution Newton - Universal Gravity F m F D M mM FG 2 D Copernican Revolution Newton - Universal Gravity Side comments: Predictability, Mechanistic universe F m1 F D mM FG 2 D Copernican Revolution m2 Copernican Revolution Newton - Universal Gravity Side comments: Predictability, Mechanistic universe Chaos theory F Why gravity? m1 F D mM FG 2 D Copernican Revolution m2 Copernican Revolution - Summary Geocentric Vs. Heliocentric Five people, contributions, significance Copernicus Brahe Kepler Galileo Newton (~1500) (~1570) (~1600) (~1600) (~1670) Process of science Copernican Revolution Science Science - A process of knowing that uncovers the laws and processes of the universe* Differs from theology or philosophy Way to get past the conflicts in various belief systems (by looking at evidence) Sagan: “It doesn’t matter if it makes you feel good. What matters is, is it true?” Process of Science* (scientific method) 1. 2. 3. 4. 5. 6. Observe Question Model (hypothesize) Predict Test Revise You use much of this process all the time in daily life Examples: Car stops…. Flashlight doesn’t work… Cooking… Three Hallmarks of Science* Natural explanations (not supernatural) Models that make testable predictions Simplest explanation; K.I.S.S. (Occam’s Razor) Theory vs. Law Vote: Which is stronger? Or more powerful? Theory !!!!!! “Oh it’s just a theory.” It is not just a theory. It is more powerful than a law. Law Explains what happens* Predicts what will happen in specific cases Ex - Universal Law of Gravity If you drop a rock, it will fall down (and what force is exerted on it) Theory Explains why things happen* Includes laws Allows predictions of new tests of itself Ex - General Theory of Relativity Explains WHY gravity works Includes the Law of Gravity AND more Explains the precession of Mercury’s perihelion Predicts the existence of Black Holes Theory Explains why things happen* Includes laws Allows predictions of new tests of itself Supported by many scientists Supported by many testable predictions Can never can be proven but has not been disproven Can always be modified, based on new data/information* Exercise Can you investigate this using science? If so, does science support the idea? If not, why not? (what hallmarks?) Ex – People get nuttier during a full Moon. Exercise Can you investigate these using science? If so, does science support the idea? If not, why not? 1. 2. 3. 4. 5. A car can skid on ice. Your personality is determined by the position of the Sun, Moon, and Planets when you were born. The universe and its contents evolve. God exists. Intelligent Design is science. Homework • • • • • • Grades are updated on class website. D2L 4 quizzes available to practice for test Test update – 50-60 multiple choice Tuesday, Feb. 7 • Bring pencil (required) & simple calculator (optional, not necessary for simple division/multiplication, some available in class) • Best test prep: 1. objectives (updated on web), 2. D2L quizzes, 3. lectures/notes, 4. textbook Observations • Sunset Part 1 Due Feb. 14 • Moon Phases Due Mar. 2 • Star Gazing, Telescopes & Moon Craters – Show options on calendar Keep up with objectives and reading the textbook Lab Students – No lab today