1 Lecture 23 The Sun January 10c, 2014 2 Basic Information • Mass = 330,000 M • Radius = 109 R • Density=1400 kg/m3 • Spins differentially – P = 25 days at equator – P = 36 days at poles • Closest star to the Earth. • Very strong magnetic field 3 Composition of the Sun • 75% Hydrogen • 24% Helium • 1% Trace elements • How do we know? – Spectroscopic measurements – Analysis of solar wind • Other important solar data comes from: – Solar and Heliospheric Observatory (SOHO) – Solar Dynamics Observatory (SDO) 4 Solar Atmosphere Corona Photosphere Interior Solar Wind Chromosphere 5 Photosphere • Layer of gas seen from the Earth • Temp ~5800 K • Granules -- patches of gas experiencing convection Cooler gas Warmer gas sinking rising 6 Chromosphere • Layer of less dense gas – Seen only during solar eclipses – Rising jets of gas = spicules 7 Corona • Seen only during a solar eclipse • Thin, hot gas (over 1 million K) • Why so hot??? – Possibly energized by magnetic field. 8 Solar Wind • Outflow of particles from Sun into space • Mainly protons and electrons. • Sun ejects 1 million tons of mass per second • Greatest wind is emitted through coronal holes 9 Sunspots • Dark, cooler (~ 4300 K) spots on surface of Sun. • Powerful magnetic field 5000× stronger than Earth’s • Lifetime of ~2 rotations (8 weeks). • More numerous in an ~11 year cycle. Sunspot motion movie Seething granules movie 10 [descriptions of movies on previous slide] Sunspot Motion Granules • The Motion of a Small Sunspot • Seething Granules Around Group Sunspots • Sunspot groups, which may last for about two months, are produced by • This time-lapse movie shows three cycles in the Sun's magnetic field. To and a half hours in the life of a measure the Sun's rotation, observers sunspot (note the clock at upper can track the motion of sunspot right). A sunspot consists of a dark groups, much as Galileo did four central umbra and a feather-like centuries ago. (This movie shows penumbra. Around them, granules these motions over a period of about some 1000 km across rise and fall two weeks.) Such studies show that in the hot photosphere. Each the equatorial regions of the Sun granule releases enough energy in rotate somewhat faster than the polar regions. its 8-minute lifetime to supply the United States with its energy needs for 300 years. 11 Sunspot photo Close up image of sunspot and granules. Click here for more info on this image 12 Solar Cycle • Last solar maximum = 2001 • Currently moving out of solar minimum = 2007 250 Smoothed Sunspot Numbers July 1749 - June 2009 from www.ngdc.noaa.gov 200 150 100 Number of Sunspots of Number 50 0 1745 1770 1795 1820 1845 1870 1895 1920 1945 1970 1995 2020 http://www.ngdc.noaa.gov/stp/SOLAR/ftpsunspotnumber.html 13 Formation of Sunspots – Sun rotates faster at the equator than at the poles – Magnetic field under surface becomes wound up – Magnetic field gets pushed above surface. – Magnetic field inhibits warmer gas from moving to those areas where field pushes through surface. 14 Sunspots are dark because A. they are cool relative to the gas around them. B. they contain 10 times more iron than the surrounding regions. C. nuclear reactions occur in them at a slower rate than in the surrounding gas. D. they are clouds in the cool corona that block our view of the solar surface. E. absorption lines are clustered together there. 15 Sunspots are dark because A. they are cool relative to the gas around them. B. they contain 10 times more iron than the surrounding regions. C. nuclear reactions occur in them at a slower rate than in the surrounding gas. D. they are clouds in the cool corona that block our view of the solar surface. E. absorption lines are clustered together there. 16 Prominences and Solar Flares • Prominences – Hot gas lofted upwards by the magnetic field. – Associated with sunspots • Solar Flares – Gas and particles erupt off of the surface – Produce sun quakes – Associated with sunspot groups 17 Prominence -- SOHO 18 Sunquake -- SOHO 19 Coronal Mass Ejection • Gigantic event sometimes set off by flares • Can create disruption of satellites, communications, and power grids 20 Flares and Coronal Mass Ejection Video Click here to view QuickTime movie 21 Solar Activity – 2004 Prediction 22 Solar minimum • In 2007-2009 the Sun entered a quieter solar activity period in more than a century • Read NASA Solar Physics article • NASA news articles in April 2009 and September 2009 23 Solar Activity – 2010 Update 24 Solar Activity – 2010 Update 25 The Energy of the Sun • Sun produces energy through the process of nuclear fusion • 4 hydrogen atoms are combined to form one helium atom He H p H p n n Energy p p H p H p 26 • During fusion, some of the mass is transferred into energy through E = energy (in Joules) E mc2 m = mass (in kg) c = speed of light = 3.0×108 m/s • Mass and energy are two manifestations of the same thing: mass-energy • Fusion can only occur in the core of the Sun – high gravitational pressure – high temperatures 27 How much total mass-energy is contained in a 55-gram candy bar? A. 170 (food) calories B. 5.0×1015 J C. 9.0×1016 J D. 5.0×1018 J 28 How much total mass-energy is contained in a 55-gram candy bar? A. 170 (food) calories B. 5.0×1015 J E mc2 16 2 C. 9.0×10 J 0.055 kg 3.0 108 m/s D. 5.0×1018 J E 5.0 1015 J 1.18 trillion food calories! Enough energy to power 62,700 homes for one year! 29 Interior Structure of the Sun • Core • Convective – Nuclear Zone fusion – Warmer produces gas moves energy upward, cool gas • Radiative sinks Zone – Energy is transported by photons of light 30 Hydrostatic Equilibrium • Balance between pressure of out-flowing energy pushing outward and inward pull of gravity. • Keeps Sun from collapsing due to gravity 31 The Sun produces its energy from A. fusion of neutrinos into helium B. fusion of positrons into hydrogen C. fission of helium into hydrogen D. fusion of hydrogen into helium E. electric currents generated in its core 32 The Sun produces its energy from A. fusion of neutrinos into helium B. fusion of positrons into hydrogen C. fission of helium into hydrogen D. fusion of hydrogen into helium E. electric currents generated in its core .