Lecture 6: Our star, the Sun

Lecture 6: Our star, the Sun 1

Age = 4.6 x 10 9 years Mean Radius = 7.0x10 5 km = 1.1x10 2 R = 1R Volume = 1.4x10 18 km 3 = 1.3x10 6 R = 1V Mass = 2x10 30 kg = 3.3x10 5 M = 1M Surface Temperature = 5,778K Rotation Period: (sidereal) at equator = 25.05 days at poles = 34.4 days SOHO (ESA & NASA) 2

"EffectiveTemperature 300dpi e" by Sch - Drawn by myself. The solar spectrum is the WRC spectrum provided by M. Iqbal: An Introduction to Solar Radiation, Academic Press 1983, Table C1. The black body spectral irradiance has been computed from a black-body spectrum for T equal 5777 K and assuming a solid angle of 6.8e-5 steradian for the source (the solar disk).. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/file:effectivetemperature_300dpi_e.png#/media/ File:EffectiveTemperature_300dpi_e.png 3

SOHO (ESA & NASA) 4

! very center of sun! high temperature and pressure " temperature is about 15.7 million K (0 o C=273K)! 20 25% of solar radius! energy generated through fusion " H->He " Fusion = two atoms forced together to form a heavier atom! Proton-Proton chain fusion reaction "FusionintheSun" by Borb - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0-2.5-2.0-1.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:FusionintheSun.svg#mediaviewer/File:FusionintheSun.svg 5

! outside of core " 0.20 0.70 of solar radius! energy transferred through radiation " H and He ions emit and reabsorb photons! radiation -> light of all wavelengths SOHO (ESA & NASA) 6

! outside of radiative zone " 0.70 of solar radius to surface! energy transferred through convection " lower temperature and density! convection -> hot gas rises, cooler gas falls! similar to boiling pot of water SOHO (ESA & NASA) 7

! Heat transfer through the motion of a hot material! When a material heats, it expands! The expanded material is less dense! The material then rises, carrying heat 9

! visible surface of sun " in visible wavelengths " T~5800K! not solid surface " <500km deep " dense enough to emit light but not so dense that light can t escape! so bright it dominates view without filters SOHO (ESA & NASA) 10

! the lower atmosphere of the sun! located above photosphere " much hotter and less dense than the photosphere! this is where most activity occurs " prominences " flares " magnetic loops "Solar eclipse 1999 4 NR" by Luc Viatour - Own work www.lucnix.be. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Solar_eclipse_1999_4_NR.jpg#mediaviewer/File:Solar_eclipse_1999_4_NR.jpg 11

! Between the chromosphere and the corona! Rapid rise in temperature " 2x10 4 K-1x10 6 K " Helium becomes fully ionized "Transition-region" by TRACE - TRACE spacecraft Picture of the Day web site http://trace.lmsal.com/ POD/images/T195_020226_03_04_filamenteruption.jpg. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/file:transition-region.jpg#mediaviewer/file:transitionregion.jpg 12

! the outer atmosphere of the sun! low density, high temperature! normally too faint to be seen " photosphere is too bright! can be seen during solar eclipse! SOHO sees by blocking out bright photosphere "Solar eclipse 1999 4 NR" by Luc Viatour - Own work www.lucnix.be. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Solar_eclipse_1999_4_NR.jpg#mediaviewer/File:Solar_eclipse_1999_4_NR.jpg 13

! What is the interior structure of the Sun?! Density " The density is highest at the center " Drops off rapidly toward surface! Temperature " The temperature is highest at the center " Drops off rapidly toward surface 14

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! Look at the following views of the sun and describe what you see! The following images and video come from the Solar and Heliospheric Observatory (SOHO) "NASA SOHO spacecraft" by Cgruda - http://sohowww.nascom.nasa.gov/gallery/images/ SOHOLower2.htmlFile:SOHO nasa.tif. Licensed under Public domain via Wikimedia Commons - http:// commons.wikimedia.org/wiki/file:nasa_soho_spacecraft.png#mediaviewer/ File:NASA_SOHO_spacecraft.png 16

! Very bright visible surface! Need filter to take picture SOHO (ESA & NASA) 17

! Darker cooler spots on the photosphere! Still very hot! Need filter to see them! Features? SOHO (ESA & NASA) 18

! As we look in other wavelengths, we see other features besides just the photosphere! Wavelength related to temperature SOHO (ESA & NASA) 19

! light and dark speckling of the photosphere! caused by convection underneath! very small scale and short time 20

! Looking in UV! Features? SOHO (ESA & NASA) 21

! Outer edges of atmosphere! Overwhelmed by photosphere! Seen in eclipses! Features? SOHO (ESA & NASA) 22

! The sun doesn t stay the same! The changes are referred to as activity 23

! Photosphere! Chromosphere! http://sohodata.nascom.nasa.gov/cgi-bin/ soho_movie_theater! Notice rotation and active regions 24

! activity increases and decreases in 11 year cycle! Called solar cycle "Sunspot Numbers". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/file:sunspot_numbers.png#mediaviewer/ File:Sunspot_Numbers.png 25

! Are we in high or low part of the cycle "Solar Cycle Prediction" by David Hathaway, NASA, Marshall Space Flight Center - http://solarscience.msfc.nasa.gov/predict.shtml. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Solar_Cycle_Prediction.gif#mediaviewer/File:Solar_Cycle_Prediction.gif 26

! the activity on the sun is caused by the magnetic field! the sun's magnetic field gets twisted and knotted SOHO (ESA & NASA) 27

SOHO (ESA & NASA) 28

! temporary cooler, darker spots on the surface! caused by magnetic field lines bunching together! last from hours to months 29

SOHO (ESA & NASA) 30

! Gas extends above the photosphere! Most visible on the edges! Features? "Sun earth jupiter whole 600" by NASA Goddard Space Flight Center - Solar Dynamics Observatory. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/ File:Sun_earth_jupiter_whole_600.jpg#/media/ File:Sun_earth_jupiter_whole_600.jpg 31

SOHO (ESA & NASA) 32

! Gas flows along the magnetic field of the prominences 33

! outbursts of activity on the sun's surface " due to magnetic reconnection! resulting in temporary brightening SOHO (ESA & NASA) 34

! Coronal Mass Ejections " large amounts of gas thrown out into space " caused by magnetic field breaking and reforming SOHO (ESA & NASA) 35

! High energy particles are ejected by the Sun! Particles interact with the Earth s magnetic field, flowing down toward the atmosphere at the poles! Produces colored light through collisions with atoms in the atmosphere " atomic excitation "Aurora Borealis and Australis Poster". Licensed under Creative Commons Attribution-ShareAlike 1.0 via Wikipedia - http://en.wikipedia.org/wiki/file:aurora_borealis_and_australis_poster.jpg#mediaviewer/ File:Aurora_Borealis_and_Australis_Poster.jpg 36

SOHO (ESA & NASA) 37

! What happens if a large Solar Storm impacts the Earth?! Geomagnetic Storms interact with the Earth s magnetic field " Coronal Mass Ejection " Solar Flare! Solar Storm Video 38