something concrete

Thursday, April 04, 2013

Chapter 10 Quiz: Olivia Ward

1. Why does the Sun shine?
   
   Gravitational contraction made the Sun's core hot enough to sustain nuclear fusion. The Sun shines because of gravitational equilibrium, which balances between the outward push of pressure and the inward pull of gravity, and energy balance between the energy released by fusion in the core and the energy radiated into space from the surface of the Sun.
2. What is the Sun's structure?
   
    The Sun's innermost layer is the core, where energy is generated by nuclear fusion. Working outward, the next layers are the radiation zone, where energy is transported upward by protons, and then the convection zone, where energy is transported upward by rising hot gas. Next lies the photosphere, the visible surface of the sun from which protons can freely escape into space. The chromosphere, the middle layer of solar atmosphere, is above the photosphere. Lastly is the outermost layer of the solar atmosphere, the corona.
3. How does nuclear fusion occur in the Sun? 
   
   The core's temperature and density allow for fusion of H into He, which occurs because of the proton-proton chain. Two protons fuse to make a deuterium nucleus. The deuterium nucleus and a proton fuse to make a nucleus of helium-3. Two helium-3 nuclei fuse to form helium-4, releasing two excess protons in the process.The fusion rate is sensitive to temperature, so gravitational equilibrium and energy balance act as a thermostat to keep the rate of fusion steady.
   
   
4. How does the energy from fusion get out of the Sun? 
   
   Energy from fusion is taken to the surface of the Sun through convection. Energy moves through the core and the radiation zone in the form of randomly bouncing photons. After the energy emerges from the radiation zone, convection carries it to the photosphere, where it is radiated as light. Energy produced in the core takes hundreds of thousands of years to reach the photosphere.
   
   
5. How do we know what is happening inside the Sun? 
   
   We know what is happening inside of the Sun through theoretical mathematical models of the solar interior which use the laws of physics which are checked through observing solar vibrations and solar neutrinos. These observations can also be checked by observing the Sun's size, surface temperature, and energy output.
6. What causes solar activity?
   
   Convection and the rotation pattern of the Sun cause solar activity. The gas motions stretch and twist the Sun's magnetic field which are responsible for sunspots, solar flares, solar prominences, and coronal mass ejections, as well as for heating the gas in the chromosphere and the corona. During periods of high solar activity, bursts of charged particles eject from the Sun which can disrupt power grids and communication satellites.
7. How does solar activity vary with time?
   
   The sunspot cycle, an 11-year cycle, refers to a variation in the number of sunspots on the Sun's surface. The magnetic field flip-flops about every 11 years. This causes a 22-year magnetic cycle.