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Why they are black (bodies)
Published online by Cambridge University Press: 05 June 2012
Gravity is the engine that drives the Universe. But it does not work alone, of course. In fact, one of the most satisfying aspects of studying astronomy is that there is a role for essentially every branch of physics when one tries to explain the huge variety of phenomena that the Universe displays. One branch of physics, however, stands out from the rest because of its absolutely central place in helping us to learn about the Universe, and that is the study of the way hot bodies give off light.
In this chapter: the colors of stars give us insight not only into the stars themselves but into the branch of physics called quantum theory, founded by Planck and Einstein. The color of light tells us the temperature of its source because light comes in particles called photons. A star's color and brightness tells us its size and distance.
Almost all of the information we have from astronomical bodies is carried to us by light, and almost all the light originates as radiation from some sort of hot region. The great breakthrough in physicists' understanding of such thermal radiation was made by the German physicist Max Planck (1858–1947) at the start of the twentieth century. (See Figure 10.2 on page 112.) The story of this breakthrough is the story of physicists' first steps toward quantum theory. It is also the story of the beginnings of a real understanding of the heavens.
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