Jessica Horn: Chapter 10 Quiz

• Why does the Sun shine? The SUn began to shine about 4.5 billion years ago when  gravitational contraction made its core hot enough to sustain nucluear fusion. It has shined steadily ever since because of two types of balance: 1. gravitational equilibrium, a balance between the outward push of pressure and the inward pull of gravity, and 2. energy balance between the energy released by fusion in the core and the energy radiated into space from the Sun's surface.
• 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 surface layer from which photons can freely escape into space. Above the photospher are the warmer chromosphere and the very hot corona.
• How does nuclear fusion occur in the Sun? The core's extreme temperature and density are just right for fusion of hydrogen into helium, which occurs via the proton-proton chain. Because the fusion rate is so sensitive to temperature, gravitational equilibrium and energy balance together act as a thermostat to keep the rate of fusion steady.
• How does the energy from fusion get out of the Sun? Energy moves through the deepest layers of the Sun-the core and the radiation zone-in the form of randomly bouncing photons. After energy emerges from the radiation zone, convection carries it the rest of the way to the photosphere, where it is radiated into space as sunlight. Energy produced in the core takes hundreds of thousands of years to reach the photosphere.
• How do we know what is happening inside the Sun? We can construct theorectical models of the solar interior using known laws of physics and then check the models against observations of the Sun's size, surface temperature, and energy output. We also use studies of solar vibrations and solar neutrinos.
• What causes solar activity? Convection combined with the rotation parttern of the Sun causes solar activity becasue gas motions stretch and twist the Sun's magnetic field. These contortions of the magnetci field are responsible for phenomena such as sunspots, solar flares, solar prominences, and coronal mass ejections, and for heating the gas in the chromosphere and corona. Bursts of charged particlesejected from the Sun during periods of high solar activity can hamper radio communications, disrupt electrical power generation, and damage orbiting satellites.
• How does solar activity vary with time? The sunspot cycle has an average period of 11 years. The magnetic field flip-flops every 11 years or so, resulting in a 22-year magnetic cycle. Sunspots first appear at mid-latitudes at solar minium, then become increasingly more common near the Sun's equator as the next minimum approaches, and sometimes dseem to be absent altogether.