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The Sun: close-up of a spectral class G main sequence star Illustration of Kirchoff’s 1st Law A hot object emits more radiation at all wavelengths than A cooler object (Figure 7-6) Structure of a Sunspot Note granulation Sunspots are regions of very strong magnetic field (2000 Gauss) Demo Sunspots represent “tubes” of magnetic field lines This causes sunspots to often occur in pairs, with opposite magnetic poles Sunspots and magnetism http://sohowww.nascom.nasa.gov/gallery/Movies/ Solar magnetic fields reach far out into space The 11 Year Solar Cycle The Sun has a “heartbeat”; its properties change on a period of 11 years Latest data on this sunspot cycle The Sunspot Cycle has been going on for a long time Observations show cycle persisting, but “turning off” from 1650 to 1730 (Maunder Minimum) The Structure of the Solar Atmosphere • • • • Photosphere Chromosphere Corona Temperature increases as you go up • Outermost layer flows out into space to form the Solar Wind The solar corona The solar corona The Solar Wind • A wind past the Earth at 400 km/sec • The Sun is “melting away” • Density 19 orders of magnitude less than atmosphere • A medium for solar events • May have “sandblasted” the early atmosphere of Mars Explosions on the Sun: Solar Flares and Coronal Mass Ejections The occurrence of flares and CMEs is enhanced around The time of solar maximum The Lesson for Other Stars • Do they also have sunspots, sunspot cycles, etc? • How does all this (magnetic fields, solar wind, rotation) relate to the age of a star?