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//In darkness born// (1988) Martin Cohen University of California, Berkeley and NASA-Ames Research Center

Chapter 1: What does astronomy tell us? This chapter is a basic overview of astronomy--why it's important, what you use it for, what questions you answer with it. There are two basic characteristics to identify stars: color and observed brightness. The two are connected in that the brighter the star, the bluer it is. Less bright stars fall closer to the red end of the spectrum. Color also plays a role in the temperature of the star. Blue stars are hotter, whereas red stars are cooler. Because of the higher temperature, blue stars also give off more energy than red ones. The visible impression that we receive represents most (but not all) of the radiation. For example, not all of the sun's light is yellow, but the peak of visible radiation from this star lies in the yellow part of the light spectrum. To calculate the amount of energy radiated by a star: you must consider the area of the visible part of the star (yes, that means just what we can see!) and the temperature of the star. (Temperature is calculated in Kelvin for these calculations.)