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Transcript
The Sun QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Chapter 10 The Sun - Our Star • “Average” star • Made entirely of gas – too hot for liquids or solids • Surface temp = 5000 K • Center temp = 10 million K • Composition (by mass): – 70% H – 28% He – 2% everything else (C, N, O, etc.) Major Regions of the Sun • Interior – Core – Radiative Zone – Convective Zone • Atmosphere – Photosphere – Chromosphere – Corona Photosphere QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this • Effective “surface” of sun – not solid – region we see by eye • Thin atmospheric layer – Few hundred km • Low density gas – 0.01% Earth’s atmosphere • Close-up shows granulation – convection cells • Sunspots – Cooler than surrounding gas • appear dark QuickTime™ and a GIF decompre ssor are n eede d to see thi s pi ctu re. Atmospheric Features • Sunspots – – – – Larger than Earth Occur in groups Associated with magnetic fields Galileo used to measure solar rotation • 25 days at equator • longer at poles – Number of sunspots • Cyclical – 11 yr period • Correlated with solar activity – greatest activity at sunspot maximum – least at minimum Most Detailed Sunspot Image Ever! QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Swedish Vacuum Telescope Solar Rotation Quic kTime™ and a GIF dec ompres sor are needed to s ee this pic ture. Atmospheric Features • Sunspots – – – – Larger than Earth Occur in groups Associated with magnetic fields Galileo used to measure solar rotation • 25 days at equator • longer at poles – Number of sunspots • Cyclical – 11 yr period • Correlated with solar activity – greatest activity at sunspot maximum – least at minimum Atmospheric Features • Prominences – Loops of hot gas – Base near sunspots – Trace magnetic fields QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Quic kTime™ and a YUV420 codec decompress or are needed to s ee this picture. Chromosphere • Region just above photosphere • Emission-line spectrum – indicates higher temperature – reddish color from hydrogen line • Temperature increases outward QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Transition Region • Between chromosphere and corona • Temperature increases – from 10,000 K to 106 K • Spicules (“spikes”) – gas jets poking up from photosphere – duration ~10 minutes – heights 5,000-20,000 km QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Corona • Outermost region of atmosphere – Extends millions of km • Seen during eclipse • Very high temperature – millions of degrees K – heated by solar magnetic field QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Solar Wind • Gas flows away from sun – 10 million tons/yr – protons & electrons – speed 400-800 km/s Quic kTime™ and a TIFF (Uncompress ed) dec ompres sor are needed to s ee this pic ture. • Material goes outward into solar system – Hits Earth’s atmosphere • guided by magnetic field • makes atmosphere glow (aurorae) QuickTi me™ and a GIF decompr essor a re needed to see this picture. Solar Flare QuickTime™ and a Photo decompressor are needed to see this picture. Solar Flares • Eruptions caused by magnetic fields QuickTime™ and a TIFF (Uncom press ed) d eco mpres sor a re n eede d to see thi s pi ctu re. – may last 5-10 min – release huge amounts of energy • gas heated to 107 K – produces X-rays and UV radiation • Coronal Mass Ejections – very large flares – large mass of gas ejected from corona Quic kTime™ and a GIF dec ompres sor are needed to s ee this pic ture. Solar Flares & Effects on Earth • CME hits Earth’s Magnetic Field – Aurorae intensified – affects magnetic field • produces power surges – ’89 Quebec/Montreal power outage – electrical interference • Disrupts radio communications – Cell phone outage • Danger to satellites/astronauts • Space Weather at: http://www.sel.noaa.gov/today.html Quick Time™a nd a Cinepa k deco mpre ssor are n eede d to s ee this picture . Solar Variability & Earth’s Climate • Solar Luminosity Varies ~1% – Highest at sunspot maximum – Lowest at minimum activity • Maunder minimum 1650-1700 – Very few sunspots – “Little Ice Age” in Europe • extreme cold temps • shorter growing season • Still learning how Sun affects Earth’s climate QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Solar Interior • Interior is gaseous • Constant battle: – Gravity pulls in – Pressure pushes out • Star shrinks – becomes hotter, until • Pressure balances gravity Hydrostatic Equilibrium Why Does Sun Shine? • Sun in Hydrostatic Equilibrium – Pressure requires high temperature – Sun is hot • Hot objects – Radiate (emit light) – lose energy Sun shines because it is hot • Solar Luminosity – 1026 Watts • Age of Sun – greater than 4.5 billion years (age of earth) • What is energy source? Sun’s Energy Source • Thermal energy (chemical reactions)? – wood or fuel burning – Entire Sun used in a few thousand years NO • Gravitational contraction? – energy released as Sun contracts – would suffice for 100 million years NO • Nuclear Energy? – Einstein: E = mc2 – Can convert mass into energy • 1 gram of matter = energy of 15,000 barrels of oil – Need 4 million tons/sec – Will suffice for 10 billion years YES Nuclear Reactions • Fusion: – two light nuclei joined into one QuickTime™ and a YUV4 20 cod ec decompre ssor are n eed ed to se e th is p icture. • Powers Sun • Fission: – massive nucleus splits in two • Powers nuclear reactors (Davis-Besse) QuickTime™ and a YUV420 codec decompressor are needed to see this picture. Converting Mass to Energy • Nuclear reactions change mass – Mass increase consumes energy – Mass decrease releases energy • Mass decreases in – Fission of heavy nuclei • Can occur spontaneously • natural radioactivity – Fusion of light nuclei • Like charges repel • Fusion requires high speed • Temperature > 10 million K QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Fusion: Sun’s Energy Source QuickTime™ and a YUV4 20 cod ec decompre ssor are n eed ed to se e th is p icture. • Sun’s core: – Temperature = 15 million K – Large enough to fuse hydrogen • p-p chain (proton-proton) – Series of fusion reactions – Converts: 4 hydrogen to 1 helium nucleus – mass of 4 H > mass of 1 He QuickTime™ and a YUV4 20 cod ec decompre ssor are n eed ed to se e th is p icture. • mass decrease is energy source QuickTime™ and a YUV4 20 cod ec decompre ssor are n eed ed to se e th is p icture. p-p Chain in the Sun