We cannot go to the stars to sample them directly. So how do we get information about the stars? We have to extract it from something that comes to us from the stars. Most commonly this “something” is light—electromagnetic radiation. To decode the information contained in the light, we have to know some things about how it is produced in the first place. What does the light tell us about the thing that is emitting the light? Ultimately, where does the light come from anyway? In this chapter, we seek answers to these questions.
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