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The Sun

The Sun. The Sun Physical Characteristics. Center of our Solar System Age ~4.6 billion years Only one of ~200billion plus stars in the Milky Way galaxy Average size and temperature Type G yellow dwarf star 99.87% of mass of the Solar System is contained in the Sun

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The Sun

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  1. The Sun

  2. The SunPhysical Characteristics • Center of our Solar System • Age ~4.6 billion years • Only one of ~200billion plus stars in the Milky Way galaxy • Average size and temperature • Type G yellow dwarf star • 99.87% of mass of the Solar System is contained in the Sun • Most of the other 0.13% of the mass is Jupiter • Diameter – 1,392,100km (12,756km) • Mass – 1.989 x 1030kg (5.97 X 1024kg) • Volume – ~1.42 x 1017 km3 (1.083 X 1012 km3) • Density – 1.62 X 105kg/m3 (5.515g/cm3) • Gravity (274m/s2 (9.78m/s2)

  3. Physical Characteristics (cont’d) • Absolute magnitude - +4.83 • Rotation (day) – 25.05 days (equator) – 34.4 days (poles) • Differential Rotation • Obliquity – 7.25degrees to ecliptic ; 67.23degrees to galactic plane • Speed relative to nearby stars – 19.4km/s • Distance from Earth 1.496 x 109 km (93million miles) • 1 AU • Effective temperature – 5778K (9,941F) • Temperature at top of chromosphere – 30,000K (53,540F) • Temp. in core 15,000,000K (26,999,540F) • “Atmosphere” • Photosphere composition – H – 90.965%, He – 8.889% • Extends beyond Earths orbit albeit very thin • Minor elements – (ppm) O,C,Ne,N,Fe,Mg,Si,S

  4. Nuclear fusion • Process of turning lighter atomic nuclei into heavier nuclei • Occurs in Sun’s core (~25% of Sun’s diameter) • H may burn to produce He but only at temperatures above 10million K • Larger, hotter stars may create heavier atoms but not the Sun • Byproducts of fusion are heat and light • The two components critical in such narrow ranges to allow life on Earth • Plasma • Gaseous phase of elements • Soup of positively charged nuclei and free negative electrons • Produces a magnetic field as it moves

  5. Hertzsprung-Russel DiagramMain Sequence Stars, etc.

  6. Sun facts • Photon Random Walk – at least a few hundred thousand yrs for a photon to get from the core to the surface & then 8 mins to us! • # of particles carried by the solar wind is about 1.3×1036 / sec • About 4–6 billion tons/hr • This is equivalent to losing a mass equal to the Earth every 150 million years (~30 Earth’s over geologic time) • Only about 0.01% of the Sun's total mass has been lost through the solar wind

  7. Total Solar Flux • The petawatt is equal to one quadrillion (1015) watts • Amount of solar energy reaching the Earth in three days is more than could be produced by all known reserves of fossil fuels • Amount of solar energy falling on the roof of the average home is enough to supply 1-3 times its energy needs • Charles Fritts was an American inventor who made the first photovoltaic cell in 1884. It operated with an efficiency of about 1% • Today’s photovoltaic cells operate at an average of 10-15%

  8. Evolution of the Sun

  9. The Suns Physical Components: Layers • Corona • Chromosphere • Photosphere • Convection Zone • Radiation Zone • Core

  10. The Suns Physical Components • Although gaseous throughout, the Sun is layered • Outermost layer is the “atmosphere” • Six zones total • Only 4 are major divisions • Some can only be seen during eclipses • Heliosphere • Extends to heliopause past orbit of Pluto where it meets the shock front boundary with the intersteller medium • Corona • Temperature is several million K • No complete theory accounts for such high temps, some heat is known to be from magnetic reconnection • Chromosphere • Thin layer ~2,000 km • Dominated by a spectrum of emission and absorption lines • Visible as a colored flash at the beginning and end of total eclipses of the Sun

  11. The Suns Physical Components • Photosphere • Sunspots – cooler, dark areas on the Suns surface • Periods lacking sunspot activity have been tied to cooler climates on Earth • Increased radiation from C14 readings in tree rings • Sunspots may be tied to magnetic field strength • Solar flares • “Small” areas heating up to 10’s of millions of degree • Throw off surges of radiation • Can impact communications • Coronal Mass Ejections (CME) • Billions of tons of charged particles escape Suns halo • Travel at millions of mph • Squash magnetic field of the Earth and dump trillions of watts of energy into the upper atmosphere • Overload power lines, destroy delicate equipment in space • Solar wind

  12. The Suns Physical Components • Corona • Highly rarefied region above the chromosphere • Extends millions of kms into space • Only visible during total solar eclipses • Temperatures > 1,000,000 K

  13. The Suns Physical Components • Chromosphere • Thin layer above photosphere • Reddish color hence name • Extends outward above the top of the convection cells, or granulation, of the photosphere • Results from the interaction of hot ionized gas with the magnetic field Hinode's Solar Optical Telescope Image credit: Hinode JAXA/NASA

  14. Granulation • Granulation is the result of turbulent eruptions of energy at the Sun’s surface due to convection cells

  15. Hot fluids or gasses rise • Cold descend or drop • If trapped in cycle a cell is created Convection Cells

  16. The Suns Physical Components (cont’d) • Convection Zone • Thermal cycles that transfer heat to the surface (photosphere) from the inner layers • Granular appearance of surface • Tachnocline • Zone where magnetic field is generated • Radiation and convection zones slide past each other • Radiation zone • Layer where some fusion occurs • Outward pressure works against gravity to keep Sun (star) stable • Core • Layer where most fusion takes place (mostly gamma rays & neutrinos) • 620 million metric tons/sec fusion rate • Not solid but 10X denser than lead • So dense it can take a photon 100,000 yrs to reach the surface and be transmitted to Earth

  17. Solar Flares • Solar flares and Coronal Mass Ejections (CME’s) • Areas on the Sun near sunspots often flare up, heating material to millions of degrees in just seconds and blasting billions of tons of material into space

  18. Coronal Mass Ejections(CME’s) • Vast bursts of EM energy across the spectrum • Ejected material is a plasma consisting primarily of electrons & protons (in addition to small quantities of heavier elements such as helium, oxygen, and iron) • Carry immense magnetic fields w/them • Can impact Earth communications, electronics, and magnetic fields • Coronal Mass Ejections range in speed from about 20 km/s to 2,700 km/s

  19. An "eruptive prominence" or blob of 60,000-degree gas, over 80,000 miles long, was ejected at a speed of at least 15,000 miles per hour. The gaseous blob is shown to the left in each image. These eruptions occur when a significant amount of cool dense plasma or ionized gas escapes from the normally closed, confining, low-level magnetic fields of the Sun's atmosphere to streak out into the interplanetary medium, or heliosphere. Eruptions of this sort can produce major disruptions in the near Earth environment, affecting communications, navigation systems and even power grids.

  20. Solar Wind • The Sun flings ~1 million tons of matter out into space every second • These particles travel at speeds of 200-800 km/sec • These particles travel past Pluto and do not slow down until they reach the termination shock within the heliosphere

  21. Solar System Map(not to scale)

  22. Solar Wind The solar wind plasma is very thin • Near the Earth, the plasma is only about 6 particles per cubic centimeter • It is responsible for such unusual things as: • auroral lights • fueling magnetospheric storms • forming a planet's magnetosphere • The particles of the solar wind, and the Sun's magnetic field (IMF) are stuck together, therefore the solar wind carries the IMF (Interplanetary Magnetic Field) with it into space

  23. Sun Spots • Mottled appearance is granulation • Result from turbulent eruptions of energy at the surface • Associated with looped magnetic field lines • Often occur in pairs of opposite magnetic polarity • SS orientation is opposite for N & S hemisphere pairs (Courtesy National Solar Observatory/Sacramento Peak)

  24. The Sunspot Cycle • 11 year cycle • Areas of intense magnetic fields • ~1000x stronger than average Sun field • Number of sunspots seen on the Sun increases from nearly zero to over 100 and then decreases to near zero again as the next cycle starts • Appear dark because they are cooler than the photosphere (the visible surface of the Sun or a star) • Umbra - Darker interior • Penumbra – lighter rim • The center of a typical sunspot is approximately 4240 k, while the solar photosphere is ~ 6000 k. • A sunspot emits enough radiation so that a single sunspot on its own in the absence of the remainder of the Sun would glow a brilliant orange-red and would be brighter than the full Moon

  25. Sunspot Count per Direct Observations

  26. Sun Spot Cycle • Sunspot counts, plotted here against an x-ray image of the Sun, have begun increasing after experiencing the lowest ss minima in over 50yrs • Previous cycle min/max plus duration are used for predictions as are changes in the Earth’s magnetic field • Current prediction for the next ss cycle max = a smoothed ss number of ~58 in July of 2013 • We are currently over 5 yrs into Cycle 24 • The predicted size would make this the smallest ss cycle in nearly 200 yrs

  27. Prediction Comparison • Independent internet blog • Predicts one of largest in 400yrs • Max ss at ~160 and peak at 2010??? (didn’t happen) • Election of Al Gore by panicked populace • Cooler Earth by 2015??? Hmmmmm…..

  28. Blankest Sun • Sept. 30, 2008: Astronomers who count sunspots have announced that 2008 is now the "blankest year" of the Space Age • As of Sept. 27, 2008, the Sun had been blank, i.e., had no visible sunspots, 200 days of the year • To find a year with more blank Suns, you have to go back to 1954, three years before the launch of Sputnik, when the Sun was blank 241 times • "Sunspot counts are at a 50-year low," says solar physicist David Hathaway of the NASA Marshall Space Flight Center. "We're experiencing a deep minimum of the solar cycle."

  29. Sunspot Activity Mar. 24th, 2014 • Low ss activity • Sun’s total solar energy output should be low • Cooler climatic conditions? • Average solar activity has little affect on overall climatic conditions • Axial tilt • Continental distribution • Ocean & its currents

  30. The Sunspot Cycle AVER sunspot is ~2X Earth’s diameter May last for several weeks Tend to form in pairs or groups, and a large group may contain up to 100 spots and may last as long as 2 months Related to C14 ratios found in tree rings Increased solar activity = decreased C14 in upper atmosphere C14 forms in atmosphere and is taken into plants for photosynthesis Tree rings w/large C14 ratios mean times of decreased sunspot activity = cooler climates http://www.youtube.com/watch?v=-PTQaOWkEfs

  31. Sun Spot Minima and Climate • Little Ice ages

  32. Sun’s Magnetic Field • 11 year cycle (22 for complete) • The Sun's magnetic poles will remain as they are now, with the north magnetic pole pointing through the Sun's southern hemisphere, until the year 2012 when they will reverse again. • This transition happens at the peak of every 11-year sunspot cycle • Interplanetary Magnetic Field (IMF) • Part of Sun’s MF that is carried by the solar wind into interplanetary space • Heliospheric Current Sheet (right)

  33. Earth’s Magnetic Field • Earth’s magnetic field also flips, but with less regularity. • Consecutive reversals are spaced 5 thousand years to 50 million years apart • The last reversal happened ~750,000 years ago • Magnetosphere – the protective bubble around our planet formed by the Earth’s magnetic field • Deflects solar wind gusts • Mars, which does not have a protective magnetosphere, has lost much of its atmosphere as a result of solar wind erosion • Magnetopause – where Earth's magnetic field and the IMF come into contact: a place where the magnetosphere meets the solar wind • Earth's magnetic field points north at the magnetopause • If the IMF points south -- a condition scientists call "southward Bz" -- then the IMF can partially cancel Earth's magnetic field at the point of contact.

  34. Earth’s Magnetic Field

  35. ExplorationRemote Sensing • Difficult because of amount of energy the Sun puts out • Earth based observing • Solar telescope – Kitt Peak, Tucson, Az. • SOHO – Solar and Heliospheric Observatory • NASA and European Space Agency cooperative effort • Coriolis • Solar Mass Ejection Imager • Monitors potentially harmful SME’s

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