The Sun

1. The Sun http://solarcellcentral.com/sun_page.html

2. Sun’s Energy • The sun composed of about 75% hydrogen and 25% helium. • At the sun’s core, nuclear fusion burns about 600 million tons of hydrogen every second, resulting in 596 million tons of helium and 4 million tons of energy. • The energy output from the sun is 385 billion billion megawatts, of which the Earth receives 95 billion megawatts (about the energy from 95 million typical sized nuclear power plants).

3. Nuclear Reactions • Nuclear Fission • A large nucleus splits into two or more smaller nuclei to become more stable • Used by nuclear power plants • Nuclear Fusion • Two hydrogen nuclei collide to form a helium atom • Fuels energy in stars

4. Structure & Features • 1. Core. • 2. Radiative Zone • 3. Convective Zone • 4. Photosphere • 5. Chromosphere • 6. Corona • 7. Sunspots • 8. Granules • 9. Prominence

5. The Core • The Core of the sun is considered to extend from the center to about 25% of the solar radius. • The Core is the only section of the sun that produces heat through fusion. • The temperature is 15,700,000 K! • The rest of the sun is heated by energy that is transferred outward from the Core. • The energy produced by fusion in the Core must travel through successive layers to the Photosphere before it escapes into space as sunlight.

6. Radiative Zone • The Radiative Zone extends from 25% to 70% of the solar radius. • The Radiative material is hot and dense enough that thermal radiation (not fusion) transfers the intense heat of the Core outward. • Heat is transferred by photon radiation. • Estimates of the "photon travel time" range from 10,000 to 170,000 years!

7. Convective Zone • The Convective Zone rotates as a normal fluid. The plasma poles rotate slowly (33.5 days) with the convection current speeds constantly increasing until they reach the plasma equator which rotates much faster (25.6 days). • In the Convective layer, from its surface down 30% of the solar radius, the solar plasma is not dense or hot enough to transfer the heat energy of the interior outward through radiation. • As a result, thermal convection occurs as thermal columns carry hot material to the Photosphere surface of the sun. • Once the material cools off at the surface, it plunges downward to the base of the Convective Zone, to absorb more heat from the top of the Radiative Zone and then repeats the cycle. • These thermal columns in the Convective Zone form an imprint on the surface of the sun and are called Solar Granules.

8. The Photosphere • The Photosphere is the visible surface of the sun. • Above the Photosphere, sunlight is free to propagate into space and its energy escapes the sun entirely. • The visible light we see is produced as electrons react with hydrogen atoms to produce hydrogen ions. • The Photosphere is hundreds of kilometers thick. • Because the upper part of the Photosphere is cooler than the lower part, an image of the sun appears brighter in the center than on the edge.

9. Shown in the diagram at the left is how the energy from the sun is distributed by wavelength and photon energy. • During early studies of the photosphere, some absorption lines were found in the solar spectrum that did not correspond to any chemicals then known on Earth. • In 1868, Norman Lockyer hypothesized that these absorption lines were a new element which he dubbed "helium", after the Greek Sun God Helios. • It was 25 years later that helium was isolated on Earth.

10. The Chromosphere • The Chromosphere is a layer of hot gases about 2,500 kilometers thick. • The Chromosphere cannot normally be seen because it is washed out by the over-whelming brightness of the Photosphere. • The temperature in the Chromosphere increases gradually, ranging from 4,000 K at its bottom to 20,000 K at the top.

11. The Corona • The Corona is the outer atmosphere of the Sun. • The average temperature of the Corona is 1,000,000 to 2,000,000 K. However, in the hottest regions it is 8,000,000 to an unbelievable 20,000,000 K! • The Corona continuously extends into outer space forming the Solar Wind.

12. Sunspots • Sunspots are a temporary phenomena on the surface of the Photosphere that appear as dark spots compared to the surrounding regions. • They are caused by intense magnetic activity, which inhibits convection, forming areas of lower surface temperatures. • Sunspots expand and contract as they move across the surface of the sun. • They can be as large as 50,000 miles in diameter making the larger ones visible from Earth.

13. Sunspots

14. Granules • Solar Granules are very hot thermal columns formed in the Convective Zone • They rise to the surface of the Photoshere, cool down, and then plunge back down to the base of the Convetive Zone, receive more heat from the Radiative Zone, then cycle up and down again. • The grainy appearance of the Photosphere is produced by the tops of these Convective cells. • A typical Granule has a diameter of about 600 miles and lasts only 8 to 20 minutes before dissipating.

16. Solar Prominence • Solar Prominences rise up through the Chromosphere from the Photosphere, sometimes reaching altitudes of 100,000 miles. • These gigantic plumes of gases, often in a loop shape, are the most spectacular of the solar phenomena. • A Prominence forms in about a day and if stable can persist in the Corona for several months. • Some Prominences break apart and morph into Coronal Mass Ejections (CMEs). • Scientists are currently researching the relationships between Solar Flares, Prominences, and CMEs. It is believed that they are all caused by intense magnetic activity.

18. Solar Flare • A solar Flare is a very large explosion on the surface of the sun with its plasma suddenly roaring to millions of degrees. • Flares occur in the active regions around Sunspots. • The Flare on the next slide occurred on August 9, 2011. The image is an extreme ultraviolet picture taken by NASA's SDO satellite. • While this Flare produced a Coronal Mass Ejection (CME), the CME was not aimed towards the earth and no local effects were observed. • The energy emitted from a Flare is about one sixth of the sun's total energy output each second. • Strong Flares eject streams of electrons, ions, and atoms (called Solar Storms) into outer space.

20. Spicule • A spicule is a flamelike jet of gas extending into the chromosphere.

21. Solar Storms • Solar Storms come in three stages. • First, high-energy sunlight, mostly x-rays and ultraviolet light, ionizes the earth's upper atmosphere, interfering with radio communications and GPS systems. Stage one takes about eight minutes to reach the earth's atmosphere. • Next comes a radiation storm, potentially dangerous to unprotected astronauts. Stage two takes from 23 minutes to two hours or more to reach earth. • Finally comes a CME, a slower moving cloud of charged particles that can take two to three days to reach earth.

23. Essential Vocabulary for Quiz • Sunspot • Granulation • Convection • Filament • Spicule • Magnetic carpet • Solar wind • Helioseismology • Nuclear fission • Nuclear fusion • Photosphere • Radiative zone • Convective zone • Differential rotation • Dynamo effect • Prominence • Flare • Aurora • CME • Solar storm • Corona • Chromosphere

24. Pg. 184 Review Questions • #1 – Why can’t you see deeper than the photosphere? • The photosphere has a high enough density that photons emitted from deeper regions are absorbed. • The negative hydrogen ions in the photosphere are excellent energy absorbers.

25. #2 – What evidence can you give that granulation is caused by convection? • Center is hotter and moving outward from center of sun • Edges are cooler and move inward toward center of sun • This follows the rules of convection… remember a lava lamp.

26. #4 – How can astronomers detect structure in the chromosphere? • Scientists use filtergrams… images taken through a filter that allows a narrow wavelength band of light through. • The spectrum of that light is then analyzed.

27. #5 – What evidence can you give that the corona has a very high temperature? • By studying its spectrum. • We observe a continuous spectrum without absorption lines but superimposed emission lines because of the ionized atoms. • Continuous spectrum tells us the electrons are moving very fast

28. #5 Continued… • Atoms in the corona are ionized due to collisions with other atoms and electrons. • These collisions require very high speeds, which means high temperatures.

29. #6 – What heats the corona and chromosphere to high temperatures? • One idea is that strong magnetic fields are responsible • Energy is stored in the magnetic field… most likely the source for solar flares. • Around the clock action of thousands of mico- and nano-flares may be able to heat the corona using the magnetic energy released.

30. #7 – How are astronomers able to explore the layers of the sun below the photosphere? • Helioseismology… • Sound waves deep in the sun move outward and cause the other layers to vibrate. • Measuring the vibrations on the surface can tell us about the material the sound waves moved through and where they originated… like earthquake waves on earth

31. #12 – What evidence can you give that sunspots are magnetic? • Sunspots show a magnetic field that is 100 times stronger than the sun’s average. • Sunspots appear in pairs with opposite ends having opposite polarity. • Pairs in NH have same polarity in leading spot while pairs in SH have opposite polarity • 11 year cycle

32. #14 – What does the spectrum of a prominence reveal? What does its shape reveal? • Spectrum • Excited, low-density gas • Emission spectrum identical to the chromosphere • Shape • Loops look like arcs associated with magnetic fields • Material must be supported by twisted loops of sun’s magnetic field

33. #15 – How can solar flares affect Earth? • They emit large amounts of x-rays and UV radiation that increase ionization in the upper atmosphere. • Large amounts of charged particles are also emitted and interact with magnetic field.

34. #17 – The lower image was recorded in the extreme UV by the SOHO spacecraft. Explain the features you see. • Bright regions are extremely hot gas trapped in magnetic fields above sunspot regions.

35. What Causes Magnetic Field? • Solar Dynamo… • Magnetic field created by moving currents of gas • Ionized gas is a good conductor • A rapidly rotating electrical conductor can create a magnetic field • Also the cause of Earth’s magnetic field