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Lecture Outline Chapter 1 The Copernican Revolution Copyright © 2010 Pearson Education, Inc. Copyright © 2010 Pearson Education, Inc. and R. Fisher In the news • http://www.space.com/27016-galaxysupercluster-laniakea-milky-wayhome.html Copyright © 2010 Pearson Education, Inc. and R. Fisher 12 sept: Chapter 1 The Copernican Revolution Copyright © 2010 Pearson Education, Inc. and R. Fisher Units of Chapter 1 Preview the chapter…. The Motions of the Planets The Birth of Modern Astronomy The Laws of Planetary Motion Newton’s Laws Summary of Chapter 1 Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.1 The Motions of the Planets The Sun, Moon, and stars all have simple movements in the sky, consistent with an Earth-centered system. But the Planets: (Show on Stellarium) •Move with respect to fixed stars • Change in brightness • Change speed • Have retrograde motion • Are difficult to describe in earth-centered system Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.1 The Motions of the Planets A basic geocentric model, showing an epicycle (used to explain planetary motions) Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.1 The Motions of the Planets Lots of epicycles were needed to accurately track planetary motions, especially retrograde motions. This is Ptolemy's model. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.1 The Motions of the Planets A heliocentric (Sun-centered) model of the solar system easily describes the observed motions of the planets, without excess complication. So, what is the primary advantage of the heliocentric model?.. Copyright © 2010 Pearson Education, Inc. and R. Fisher *13 sept; 1.2 The Birth of Modern Astronomy Observations of Galileo: • The Moon has mountains, valleys, and craters. • The Sun has imperfections, and it rotates. • Jupiter has moons. • Venus has phases. All these were in contradiction to the general belief that the heavens were constant, perfect, and immutable. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.2 The Birth of Modern Astronomy The phases of Venus are impossible to explain in the Earth-centered model of the solar system. Copyright © 2010 Pearson Education, Inc. and R. Fisher The birth of modern astronomy • https://www.youtube.com/watch?v=zHU WP9zu4W8 • Watch until 10:45. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.3 The Laws of Planetary Motion Kepler’s laws: 1. Planetary orbits are ellipses, Sun at one focus. Copyright © 2010 Pearson Education, Inc. and R. Fisher **1.3 The Laws of Planetary Motion Kepler’s laws: 2. Imaginary line connecting Sun and planet sweeps out equal areas in equal times. When an orbiting planet or comet is near the sun, it goes fast, and Copyright © 2010it’s Pearson Education, Inc. and R.it Fisher when far away, goes slowly. 1.3 The Laws of Planetary Motion Kepler’s laws: 3. Square of period of planet’s orbital motion is proportional to cube of semimajor axis. The period of a planet goes up as the radius of the planet increases Copyright © 2010 Pearson Education, Inc. and R. Fisher Compare this to Kepler’s second law. Who was Kepler? • • • • The greatest astronomer. Born 1571. Worked for Tycho Brahe (“teesho”) Analyzed motion of the planets, worked out laws of planetary motion • a good and interesting 20 min video of this history • http://www.youtube.com/watch?v=IBvMhpx8Q0Q plus http://www.youtube.com/watch?v=ShQXRBDBfaA Copyright © 2010 Pearson Education, Inc. and R. Fisher From this video, know • • • • • • • • Aritotle Ptolomy Renaissance Copernicus Tycho brahe Kepler Galileo Newton Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.3 The Laws of Planetary Motion The Dimensions of the solar system • The distance from Earth to the Sun is called an astronomical unit. Its actual length may be measured by bouncing a radar signal off Venus and measuring the transit time. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.4 Newton’s Laws Newton’s laws of motion explain how objects interact with the world and with each other. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.4 Newton’s Laws Newton’s third law: know this one!!!! When object A exerts a force on object B, object B exerts an equal and opposite force on object A. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.4 Newton’s Laws Gravity On Earth’s surface, the acceleration due to gravity is approximately constant, and directed toward the center of Earth. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.4 Newton’s Laws Gravity For two massive objects, the gravitational force is proportional to the product of their masses divided by the square of the distance between them. The closer they are, or the bigger (more massive) they are, the harder they pull on each other. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.4 Newton’s Laws Gravity The gravitational pull of the Sun keeps the planets moving in their orbits. Compare to a spinning ball on string…. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.4 Newton’s Laws Two or more Massive objects orbit around each other. look at http://phet.colorado.edu/sims/my-solarsystem/my-solar-system_en.html and see binary star or double double to see various types of orbit. Or look at http://phet.colorado.edu/en/simulation/gravityand-orbits to see earth wobble the sun. Copyright © 2010 Pearson Education, Inc. and R. Fisher 1.4 Newton’s Laws Kepler’s laws are a consequence of Newton’s laws. Copyright © 2010 Pearson Education, Inc. and R. Fisher 18 sept. Quiz on chapter 2 1. 2. The shape of every orbit is a. Circle b. square c. parabola d. ellipse Which was NOTan observation of Galileo? a. The Moon has mountains, valleys, and craters. B. The Sun has imperfections, and it rotates. C. Jupiter has moons. D. Venus has moons 3. Which of these people was NOT part of the Copernican revolution a. Copernicus b. Aristotle c. Kepler d. Newton 4. What is the force that holds all planets, moons, comets, asteroids, galaxies, and stars in their orbits? a. Gravity b. Magnetism Copyright © 2010 Pearson Education, Inc. and R. Fisher c. Jedi d. Mass 18 Sept 2015 • • • • • • • • • Quiz on Stelarium Find your object Any moons? Their period Magnitude, phases Look at variation with time Why change size Moon on sept 27, 9:40pm Turn on equatorial grid Find your zodiac constellation Where was the moon when you were born? Copyright © 2010 Pearson Education, Inc. and R. Fisher Summary of Chapter 1 • First models of solar system were geocentric, but couldn't easily explain retrograde motion. • Heliocentric model does. • Galileo's observations supported heliocentric model. • Kepler found three empirical laws of planetary motion from observations. Copyright © 2010 Pearson Education, Inc. and R. Fisher The varieties of orbital motion • http://phet.colorado.edu/sims/my-solarsystem/my-solar-system_en.html • Look at the range of possibilities • Check: why are only stable orbits present in our solar system & galaxy? • Are all orbits stable? Examples…. Copyright © 2010 Pearson Education, Inc. and R. Fisher Summary of Chapter 1, cont. • Laws of Newtonian mechanics explained Kepler’s observations. • Gravitational force between two masses is proportional to the product of the masses, divided by the square of the distance between them. Copyright © 2010 Pearson Education, Inc. and R. Fisher Update on New Horizons http://pluto.jhuapl.edu/ Copyright © 2010 Pearson Education, Inc. and R. Fisher Show this tool in google earth Copyright © 2010 Pearson Education, Inc. and R. Fisher • NY Times yesterd ay Copyright © 2010 Pearson Education, Inc. and R. Fisher Practice for exam 1 • 1) In an annular eclipse, A) the Moon is totally blocked by the Earth. B) the Sun is partially blocked by the Earth. C) the Moon appears as a thin, bright ring. D) the Sun appears as a thin, bright ring. E) the Sun is totally blocked by the Moon. • 2) The interval from new Moon to first quarter is about a(n) A) month. B) day. C) hour. D) year. E) week. • 3) Put these important scientists in proper order of when they lived and worked a. Galileo, b. Copernicus, c. Newton, d. Ptolomy, e. Kepler Copyright © 2010 Pearson Education, Inc. and R. Fisher