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Chapter 15The Sun
Luminosity – total energy radiated by the Sun – can be calculated from the fraction of that energy that reaches Earth.
This diagram illustrates how one can extrapolate from the radiation hitting Earth to the entire output of the Sun.
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Chapter 15The Sun
Mathematical models, consistent with observation and physical principles, provide information about the Sun’s interior.
In equilibrium, inward gravitational force must be balanced by outward pressure
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Chapter 15The Sun
Although the average density of the Sun is only slightly more dense than water the density at the core is extremely high.
The temperature is relatively low at the surface but is near 15 million K in the core.
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Chapter 15The Sun
The Solar interior has been understood theoretically for years. In recent years we have been able to investigate it by observation. Doppler shifts of solar spectral lines indicate a complex pattern of vibrations that can be used much like seismic waves on the Earth to determine the interior construction of the Sun.
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Chapter 15The Sun
Energy transport in gases is limited to convection and radiation. In the radiation zone the particles are so tightly packed that the energy can only pass by radiation.
The radiation zone is relatively transparent; the cooler convection zone is opaque.
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Chapter 15The Heart of the Sun
Before we can discuss how the heat of the Sun is generated we have to consider the following:
Four Forces of Nature Force StrengthStrong Nuclear (pull) 1040
Electro-Magnetic 1028
Weak Nuclear (push) 1026
Gravitational 1
Einstein’s famous equation for the equivalence of matter and energy
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Chapter 15The Sun
This is the first step in the three-step fusion process that powers most stars.
Proton –Proton Chain
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Chapter 15The Sun
The ultimate result of the process is:
The helium stays in the core;
The energy is in the form of gamma rays, which gradually share their energy with the body of the Sun as they travel out from the core, emerging in all of the wavelengths of the electromagnetic spectrum;
The neutrinos escape without interacting.
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Chapter 15
The Solar Atmosphere
The cooler chromosphere, is the pink layer above the photosphere. It is hard to see directly as the sun is too bright, unless Moon completely covers the photosphere. The much less dense corona can also be seen during a total eclipse. Temperatures here range from 1 to 4 million K.
The Sun Astro1010-lee.com
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Chapter 15The Sun
Solar corona changes along with sunspot cycle; it is much larger and more irregular at sunspot peak
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Chapter 15Features of the the Sun’s Surface A
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Chapter 15The Sun
The visible top layer of the Sun, the Photo-sphere, is the top convection zone and is granulated. The areas of upwelling hot gas are light, surrounded by areas of sinking cooler gas.
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Chapter 15The Sun
Sunspots are the most fascinating of all the solar features. Galileo saw them in 1610 and they have been studied actively ever since. They appear dark because they are slightly cooler than the surroundings. The dark central part is the umbra and lighter surrounding part is the penumbra
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Chapter 15The Sun
The Sun reverses magnetic polarity every 11 years. Sun spots cycle through a maximum every polarity cycle . It takes two 11 year half-cycles to make one full 22 year cycle
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Chapter 15U
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The Solar Surface
They are like the ends of bar magnets with lines of force looping between them.
Schematic Formation of Sunspots : Notice the interaction between magnetic field lines and the differential rotation. Magnetic lines trapped in the plasma stretch and break to form Sun Spots
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Chapter 15The Sun
The number of Sunspots go through a maximum each half cycle. Some half cycles show more activity than others.
At the beginning of a half cycle most of the Sun spots are near 30 degrees north and south. By the end most are nearer the equator
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Chapter 15The Sun
Over the years efforts have been made, with few successes, to correlate sun spot activity with events on the Earth. The coincidence of the Maunder minimum with the mini-ice-age in Europe is often designated as a cause-and-effect.
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Chapter 15The Sun
A Solar flare is a large explosion on Sun’s surface, driving matter into space in seconds or minutes. This matter adds to the Solar Wind,
Hot matter escapes Sun often through coronal holes in Coronal Mass Ejections, which can be seen in X-ray images as bright white spots
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Chapter 15The Sun
Neutrinos are emitted directly from the core of the Sun, and escape, interacting with virtually nothing. Being able to observe these neutrinos would give us a direct picture of what is happening in the core. Unfortunately, they are no more likely to interact with Earth-based detectors than they are with the Sun; the only way to spot them is to have a huge detector volume and to be able to observe single interaction events.
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Chapter 15The Solar Surface
This is a large solar neutrino detector. Interactions (dim flashes) take place in the liquid, which reaches the top of the dome when full, Detection is by the glass photomultiplier tubes.
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Chapter 15The Solar Surface
Detection of solar neutrinos has been going on for more than 30 years now; despite very different detection methods and energy sensitivities, all experiments agree that they are seeing about 30–50% of the expected number of neutrinos. Could be:
• Problem with solar model
• Problem with our understanding and detection of neutrinos
The second option seems more likely today.
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