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## Introduction To Modern Astronomy II

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**ASTR 113 – 003**Spring 2006 Lecture 01 Jan. 25, 2006 Introduction To Modern Astronomy II Dr. Jie Zhang jzhang7@gmu.edu (703)993-1998**ASTR 113 – 003**Spring 2006 Syllabus • Objectives • Get to know our universe, across the space and the time • Learn the reasoning and critical thinking • The second course in a two-semester series • Associated with a Lab (ASTR 114) • Math helps, algebra and geometry**ASTR 113 – 003**Spring 2006 Syllabus • One more objective: enjoy • Milky Way Galaxy (VTS_40_1) • Galaxy Interaction (VTS_17_1) • Hubble in 15 years (VTS_37_1)**ASTR 113 – 003**Spring 2006 Syllabus • Studying Tips • Before class, reading and preparing yourself • In class, concentrate on thinking, reasoning and understanding, but not only memorizing. • Exam questions are mostly based on your understanding. • In class, taking note • Do not lag behind; hard to catch up later**ASTR 113 – 003**Spring 2006 Syllabus • Homework & Projects: none (but the lab) • Three 1-hour-long In-Class Exams • One Final Exam • All multiple choice type questions • Closed book and closed note • Need ID, Scantron (Bring your own), pencils and calculators only**ASTR 113 – 003**Spring 2006 Syllabus • Grading • Final exam: 40% • Three IN-CLASS Exam: 60% • one lowest score is dropped • No Make-up Exams • Do not miss the exam • Do not be late coming to the exam • No Extra Credit**ASTR 113 – 003**Spring 2006 Honor Code "George Mason University shares in the tradition of an honor system that has existed in Virginia since 1842. The Honor Code is an integral part of university life. On the application for admission, students sign a statement agreeing to conform to and uphold the Honor Code. Therefore, students are responsible for understanding the provisions of the code. In the spirit of the code, a student's word is a declaration of good faith acceptable as truth in all academic matters. Therefore, cheating and attempted cheating, plagiarism, lying, and stealing of academic work and related materials constitute Honor Code violations. To maintain an academic community according to these standards, students and faculty must report all alleged violations of the Honor Code to the Honor Committee. Any student who has knowledge of, but does not report, an Honor Code violation may be accused of lying under the Honor Code."**ASTR 113 – 003**Spring 2006 Contact Information • Office Hour: Wednesday 2:00 – 4:00 PM • Other meetings by appointment • Class website: http://solar.scs.gmu.edu/teaching/ASTR113_2006/index.html • Presentations will be posted, usually before the class • Office: Room 111, Science and Technology Building 1 • Telephone: (703)993-1998 • Fax: (703)993-1993 • E-mail: jzhang7@gmu.edu • Mail-add: MSN 5C3, George Mason University**ASTR 113 – 003**Spring 2006 Review on Physical Laws • Kepler’s (1571) Law on Planetary Motion (Chap04) • Newton’s (1642) Law on Motion and Gravity (Chap04) • Maxwell’s (1831) Equation on Electromagnetism (Chap04) • Wien’s (1864) Law on Blackbody Spectrum (Chap05) • Stefan-Boltzmann Law on Blackbody Energy (Chap05) • Kirchoff’s (1824) Law on Spectrum (Chap05) • Bohr’s (1992) Model on Atom (Chap05) • Doppler (1803) Effect (Chap05)**Kepler’s First Law**• Planets orbit the Sun in ellipse with the Sun at one focus**Kepler’s Second Law**• Planets sweep out equal areas in equal times • Travel faster when closer, slower when further**Kepler’s Third Law**• Orbital Period squared is proportional to semi-major axis cube P2 = a3 P = planet’s sidereal period, in years a = planet’s semimajor axis, in AU**Newton’ three Laws of Motion**• Isaac Newton developed three principles, called the laws of motion, that apply to the motions of objects on Earth as well as in space • These are • the law of inertia: a body remains at rest, or moves in a straight line at a constant speed, unless acted upon by a net outside force • F = m x a (the force on an object is directly proportional to its mass and acceleration) • the principle of action and reaction: whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body**Newton’s Law of Gravitation**F = gravitational force between two objects m1 = mass of first object m2 = mass of second object r = distance between objects G = universal constant of gravitation • If the masses are measured in kilograms and the distance between them in meters, then the force is measured in newtons • Laboratory experiments have yielded a value for G of G = 6.67 × 10–11 newton • m2/kg2**Maxwell’s Law on Electromagnetism**Don’t worry about notation here • Electricity according to Gauss • relates electricity to electric charge • Faraday’s Law • relates electric fields to magnetic fields • Magnetism according to Gauss • relates magnetism to electricity • Ampere-Maxwell Law • relates magnetic field to electricity**The Nature of Light**• In the 1860s, the Scottish mathematician and physicist James Clerk Maxwell succeeded in describing all the basic properties of electricity and magnetism in four equations • This mathematical achievement demonstrated that electric and magnetic forces are really two aspects of the same phenomenon, which we now call electromagnetism**The Nature of Light**• light is also called electromagnetic radiation • Visible light falls in the 400 to 700 nm range • Stars, galaxies and other objects emit light in all wavelengths**Light has properties of both waves and particles**• Newton thought light was in the form of little packets of energy called photons and subsequent experiments with blackbody radiation indicate it has particle-like properties • Young’s Double-Slit Experiment indicated light behaved as a wave • Light has a dual personality; it behaves as a stream of particle like photons, but each photon has wavelike properties**Photon Energy**• Planck’s law relates the energy of a photon to its frequency or wavelength E = energy of a photon h = Planck’s constant c = speed of light • = wavelength of light ν= frequency of light • The value of the constant h in this equation, called Planck’s constant, has been shown in laboratory experiments to be h = 6.625 x 10–34 J s E = h ν**Wien’s Law**• Wien’s law states that the dominant wavelength at which a blackbody emits electromagnetic radiation is inversely proportional to the Kelvin temperature of the object**Blackbody**• A blackbody is a hypothetical object that is a perfect absorber of electromagnetic radiation at all wavelengths • Stars closely approximate the behavior of blackbodies, as do other hot, dense objects • The intensities of radiation emitted at various wavelengths by a blackbody at a given temperature are shown by a blackbody curve**Stefan-Boltzmann Law**• The Stefan-Boltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux F directly proportional to the fourth power of the Kelvin temperature T of the object: F = T4 F: energy flux, in joules per square meters per second T: object temperature σ : a constant**Kirchoff’s Laws on Spectrum**• Three kinds of Spectrum • Continuous Spectrum • Emission Spectrum • Absorption Spectrum**Kirchoff’s First Spectral Law**• A hot opaque body, such as a perfect blackbody, or a hot, dense gas produces a continuous spectrum – a complete rainbow of colors without any spectral lines. • digitally like this Intensity Wavelength**Kirchoff’s Second Spectral Law**• A hot, transparent gas produces an emission line spectrum – a series of bright spectral lines against a dark • or digitally like this Intensity Wavelength**Kirchoff’s Third Spectral Law**• A cool, transparent gas in front of a continuous spectrum produces an absorption line spectrum – a series of dark spectral lines among the colors of the continuous spectrum • or digitally like this Intensity Wavelength**Bohr’s Model of Atom**• The nucleus of an atom is surrounded by electrons that occupy only certain orbits or energy levels • When an electron jumps from one energy level to another, it emits or absorbs a photon of appropriate energy (and hence of a specific wavelength). • The spectral lines of a particular element correspond to the various electron transitions between energy levels in atoms of that element. • Bohr’s model of the atom correctly predicts the wavelengths of hydrogen’s spectral lines.**Doppler Effect**• Red Shift: The object is moving away from the observer • Blue Shift: The object is moving towards the observer Dl/lo = v/c Dl = wavelength shift lo = wavelength if source is not moving v = velocity of source c = speed of light