Chapter 10

Chapter 10 - Note that the following lectures include...

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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).
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The Interstellar Medium Chapter 10
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In a discussion of bread baking, we might begin with a chapter on wheat and flour. In our discussion of the birth and death of stars, the theme of the next five chapters, we begin with a chapter about the gas and dust between the stars. It is the flour from which nature bakes stars. This chapter clearly illustrates how astronomers use the interaction of light and matter to learn about nature on the astronomical scale. That tool, which we developed in Chapter 7, “Starlight and Atoms,” is powerfully employed here, especially when we include observations at many different wavelengths. We also see in this chapter the interplay of observation and theory. Neither is useful alone, but together they are a powerful method for studying nature, a method generally known as science. Guidepost
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I. Visible-Wavelength Observations A. Nebulae B. Extinction and Reddening C. Interstellar Absorption Lines II. Long- and Short-Wavelength Observations A. 21-cm Observations B. Molecules in Space C. Infrared Radiation from Dust D. X Rays From the Interstellar Medium E. Ultraviolet Observations of the Interstellar Medium III. A Model of the Interstellar Medium A. Four Components of the Interstellar Medium B. The Interstellar Cycle Outline
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A World of Dust We are interested in the interstellar medium because a) dense interstellar clouds are the birth place of stars b) Dark clouds alter and absorb the light from stars behind them The space between the stars is not completely empty, but filled with very dilute gas and dust, producing some of the most beautiful objects in the sky .
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Bare-Eye Nebula: Orion One example of an interstellar gas cloud (nebula) is visible to the bare eye: the Orion nebula
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Three Kinds of Nebulae (1) 1) Emission Nebulae Hot star illuminates a gas cloud; excites and/or ionizes the gas (electrons kicked into higher energy states); electrons recombining, falling back to ground state produce emission lines. The Fox Fur Nebula NGC 2246 The Trifid Nebula
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Three Kinds of Nebulae (2) Star illuminates gas and dust cloud; star light is reflected by the dust; reflection nebula appear blue because blue light is scattered by larger angles than red light; Same phenomenon makes the day sky appear blue (if it’s not cloudy). 2) Reflection Nebulae
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Scattering in Earth’s Atmosphere (SLIDESHOW MODE ONLY)
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Three Kinds of Nebulae (3) Dense clouds of gas and dust absorb the light from the stars behind; Bernard 86 Horsehead Nebula appear dark in front of the brighter background; 3) Dark Nebulae
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Red light can more easily penetrate the cloud, but is still absorbed to some extent Interstellar Reddening Infrared Blue light is strongly scattered and absorbed by interstellar clouds Infrared radiation is hardly absorbed at all Interstellar clouds make background stars appear redder Visible Barnard 68
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Interstellar Reddening (2) The Interstellar Medium absorbs light more strongly at shorter wavelengths.
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Chapter 10 - Note that the following lectures include...

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