Chapter 07

Chapter 07 - Note that the following lectures include...

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Unformatted text preview: Note that the following lectures include animations and PowerPoint effects such as fly ins and transitions that require you to be in PowerPoint's Slide Show mode (presentation mode). Starlight and Atoms Chapter 7 Some chapters in textbooks do little more than present facts. The chapters in this book attempt to present astronomy as organized understanding. But this chapter is special. It presents us with a tool. The interaction of light with matter gives astronomers clues about the nature of the heavens, but the clues are meaningless unless astronomers understand how atoms leave their traces on starlight. Thus, we dedicate an entire chapter to understanding how atoms interact with light. This chapter marks a transition in the way we look at nature. Earlier chapters described what we see with our eyes and explained those observations using models and theories. With this chapter, we turn to modern astrophysics, the application of physics to the study of Guidepost the sky. Now we can search out secrets of the stars that lie beyond the grasp of our eyes. If this chapter presents us with a tool, then we should use it immediately. The next chapter will apply our new tool to understanding the sun. Guidepost (continued) I. Starlight A. Temperature and Heat B. The Origin of Starlight C. Two Radiation Laws D. The Color Index II. Atoms A. A Model Atom B. Different Kinds of Atoms C. Electron Shells III. The Interaction of Light and Matter A. The Excitation of Atoms B. The Formation of a Spectrum Outline IV. Stellar Spectra A. The Balmer Thermometer B. Spectral Classification C. The Composition of the Stars D. The Doppler Effect E. Calculating the Doppler Velocity F. The Shapes of Spectral Lines Outline (continued) The Amazing Power of Starlight Just by analyzing the light received from a star, astronomers can retrieve information about a stars 1. Total energy output 2. Surface temperature 3. Radius 4. Chemical composition 5. Velocity relative to Earth 6. Rotation period Color and Temperature Orion Betelgeuse Rigel Stars appear in different colors, from blue (like Rigel) via green / yellow (like our sun) to red (like Betelgeuse). These colors tell us about the stars temperature. Black Body Radiation (1) The light from a star is usually concentrated in a rather narrow range of wavelengths. The spectrum of a stars light is approximately a thermal spectrum called a black body spectrum . A perfect black body emitter would not reflect any radiation. Thus the name black body. Two Laws of Black Body Radiation 2. The peak of the black body spectrum shifts towards shorter wavelengths when the temperature increases. Wiens displacement law : max 3,000,000 nm / T K (where T K is the temperature in Kelvin)....
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This note was uploaded on 11/04/2011 for the course PHYS 227 taught by Professor Professorroberts during the Fall '11 term at BYU.

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Chapter 07 - Note that the following lectures include...

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