Chapter 10 Summary

Chapter 10 Summary - M10_BENN0885_05_SE_C10.qxd 9/29/08...

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302 Part IV Stars the Sun’s core. After a journey through the solar interior lasting sev- eral hundred thousand years and an 8-minute journey through space, a small fraction of this energy reaches Earth and supplies sun- light and heat. Gravitational equilibrium, the balance between pressure and gravity, determines the Sun’s interior structure and helps create a natural thermostat that keeps the fusion rate in the Sun steady. If the Sun were not so steady, life on Earth might not have been possible. The Sun’s atmosphere displays its own version of weather and cli- mate, governed by solar magnetic Felds. Some solar weather, such as coronal mass ejections, clearly affects Earth’s magnetosphere. Other claimed connections between solar activity and Earth’s cli- mate may or may not be real. The Sun is important not only as our source of light and heat, but also because it is the only star near enough for us to study in great detail. In the coming chapters, we will use what we’ve learned about the Sun to help us understand other stars. summary of key concepts 10.1 A Closer Look at the Sun • Why does the Sun shine? The Sun shines because gravitational equilibrium keeps its core hot and dense enough to release energy through nuclear fusion. The core originally be- came hot through the release of energy by gravitational contraction , as grav- ity made the Sun’s birth cloud contract. • What is the Sun’s structure? The Sun’s interior layers, from the inside out, are the core , the radiation zone , and the convection zone . Atop the convection zone lies the photosphere , the layer from which photons can freely escape into space. Above the photosphere (essentially the surface of the Sun) are the warmer chromosphere and the very hot corona . 10.2 Nuclear Fusion in the Sun • How does nuclear fusion occur in the Sun?
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Chapter 10 Summary - M10_BENN0885_05_SE_C10.qxd 9/29/08...

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