At least 95% of the celestial information we receive is in the form of light. Because of this fact, astronomers have devised many techniques to decode as much as possible the messages that are encoded in the often extremely faint rays of light. These messages include information about the object's temperature, motion, chemical composition, gas density, surface gravity, shape, structure, and more! Roughly 85% of the information in light is uncovered by using spectroscopy---spreading the light out into its different constituent colors or wavelengths and analyzing the spectrum. The first part of this chapter covers the characteristics of all forms of light and the following sections cover spectroscopic analysis. The vocabulary terms are in boldface.
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last updated: January 7, 2011