class15a - Topics for this week What can we learn about...

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Topics for this week What can we learn about stars from their spectra? How does the Sun generate the energy that is radiated from its surface? Describe the first reaction in the proton-proton chain of nuclear reactions in the Sun. What is the overall result of the nuclear reactions in the Sun? How does Einstein’s equation, E = m c 2 , help explain how nuclear reactions generate energy? Describe how neutrinos allow us to observe the interior of the Sun, and say what was found.
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Information in spectra What can we learn about stars from their spectra? composition: different atoms emit and absorb light at different wavelengths. motion: from the shift in wavelength caused by the Doppler effect we can measure a star’s motion toward or away from us. We can also measure their rotation this way. temperature: hot stars emit their light at shorter wavelengths than cooler stars do. They also have different patterns of absorption and emission lines. age size mass
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Spectra of stars The deep layers of the atmospheres of stars emit light according to the rules for radiation from solids (although they aren’t actually solid). The outer layers of atmospheres of stars produce emission and absorption line spectra. Studies of the spectra of stars tell us about both the temperatures and the compositions of their atmospheres. The simplest effect of temperature is that hotter stars appear bluer and cooler stars appear redder, but temperature changes spectra in other ways too.
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Spectra of Stars Hot stars emit more short wavelength light than cooler stars do because atoms in hot stars have more energy than atoms in cooler stars do, so they can emit higher energy photons, which have shorter wavelengths.
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