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The Sun Astronomy 311 Professor Lee Carkner Lecture 23 Helios -- The God of the Sun The Sun was often worshiped by ancient people WARNING ! NEVER LOOK DIRECTLY AT THE SUN NEVER LOOK AT THE SUN WITH BINOCULARS OR A TELESCOPE PERMANENT EYE DAMAGE CAN RESULT Observing the Sun With a solar filter in place we can use a telescope to get a high spatial resolution optical image of the Sun Today’s Sun The Sun From the Inside Out We will examine the Sun from the core to the diffuse outer layers Nuclear fusion and magnetic fields play key roles in the energetics and structure of the Sun Why Does the Sun Shine? From radioisotope dating we know that the solar system is 4.5 billion years old What could power the Sun for this length of time? The Core At the core of the Sun the temperature and pressure are very high due to the weight of the outer layers At these conditions the hydrogen atoms are moving so fast and are packed together so tightly that they can fuse together to make helium: Hydrogen Fusion How Does the Energy at the Core Get Out? In general energy is transported in 3 ways: Conduction -Radiation -Convection -- The Inner Structure of the Sun Radiative and Convective Zones Radiative Zone (0.25-0.71 Rsun) Convective Zone (0.71-1.00 Rsun) Hot material rises causing convection The Photosphere It takes about 170,000 years for the energy to reach the surface of the Sun The photosphere has an average temperature of 5800 K The top layer will absorb some of the light from the bottom layers producing absorption lines Granulation in the Photosphere The photosphere is at the top of the convective zone The photosphere is covered with granules (each about 1000 km across) Solar Granulation Granules Sunspots in the Photosphere The photosphere sometimes has small dark regions called sunspots Sunspots are regions where the Sun’s magnetic field inhibits the flow of warmer material Sunspots Sunspot Cycles Sunspots exist for a maximum of a few months There is a sunspot cycle of 11 years The sunspots move towards the equator over the course of the cycle Sunspot Maximum and Minimum The Sunspot Cycle Sunspot Cycles and Differential Rotation The Sun rotates differentially The magnetic field gets “wrapped-up” around the equator The sunspots are caused by the magnetic field “kinks” The Twisted Magnetic Field of the Sun The Sun’s Magnetic Field The Sun’s magnetic field extends far out beyond the surface These loops can break and reconnect The Chromosphere The chromosphere is a diffuse layer of the solar atmosphere extending from the photosphere to about 2000 km It has a temperature of about 20000 K The Structure of the Chromosphere The chromosphere is composed of many rising filaments of hot gas called spicules Between the chromosphere and the corona is the transition region where the temperature rises from 20,000 K to 1 million K over a small region Spicules in the Chromosphere Temperature in the Sun’s Atmosphere The Corona The corona is the outer layer of the Sun’s atmosphere It is thinner and hotter than the chromosphere The high temperatures produce a hot ionized gas called a plasma Flares and Magnetic Activity The material in the corona is constantly changing Flare activity is linked to sunspot activity Changes in magnetic activity seem to effect climate Magnetic Activity Cycle The Structure of the Corona The high temperatures and irregular structure of the corona are due to magnetic fields The tangled, shifting magnetic loops gives the corona its structure Core Radiative Zone Convective Zone Photosphere Chromosphere Corona Structure of the Sun Summary: Structure of the Sun Core fusion converts H to He and power the Sun Radiative Layer transports energy from the core Convective Layer transports energy to the photosphere Photosphere visible surface of the Sun Chromosphere hot middle atmospheric layer Corona very hot outer layer Summary: Solar Energetics Thermonuclear Fusion Energy is produced at the core of the Sun by converting hydrogen to helium Energy Transport Energy is transported via radiation where the opacity is low and via convection where the opacity is high Magnetic Fields The outer layers of the Sun are composed of hot plasma in magnetic loops
