4. Spectroscopy - The Inner Workings of Atoms

The Inner Workings of Atoms

This illustration shows the complete visible spectrum of the giant star Arcturus. By passing the star's light through a prism, the light is spread out into its component colors, displayed here wrapped around row after row from red at top left to blue at bottom right. Each of the 50 rows covers 8 nanometers in wavelength, for complete coverage of the visible spectrum from 300 to 700 microns. The many dark lines are caused by light from the hot star being absorbed by specfic atoms and ions in the star's cooler atmoshpere. (NOAO) The Big Picture: Spectroscopy is a powerful observational technique enabling scientists to infer the nature of matter by the way it emits or absorbs radiation. Not only can spectroscopy reveal the chemical composition of distant stars and yield knowledge of how they shine, it can also provide a wealth of information about the birth, evolution, and death of myriad objects in the Universe.

		LEARNING GOALS
		Studying this chapter will enable you to:
		Describe the characteristics of continuous, emission, and absorption spectra and the conditions under which each is produced.
		Explain the relation between emission and absorption lines and what we can learn from these lines.
		Specify the basic components of the atom and describe our modern conception of its structure.
		Discuss the observations that led scientists to conclude that light has particle as well as wave properties.
		Explain how electron transitions within atoms produce unique emission and absorption features in the spectra of those atoms.
		Describe the general features of spectra produced by molecules.
		List and explain the kinds of information that can be obtained by analyzing the spectra of astronomical objects.

The wave description of radiation allowed nineteenth-century astronomers to begin to decipher the information reaching Earth from the cosmos in the form of visible and invisible light. However, early in the twentieth century, it became clear that the wave theory of electromagnetic phenomena was incomplete—some aspects of light simply could not be explained purely in wave terms. When radiation interacts with matter on atomic scales, it does so not as a continuous wave but in a jerky, discontinuous way—in fact, as a particle. With this discovery, scientists quickly realized that atoms, too, must behave in a discontinuous way, and the stage was set for a scientific revolution that has affected virtually every area of modern life. In astronomy, the observational and theoretical techniques that enable researchers to determine the nature of distant atoms by the way they emit and absorb radiation are now the indispensable foundation of modern astrophysics.

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