ASTR 1102 002 2008 Fall Semester Joel E Tohline Alumni Professor Office 247 Nicholson Hall Slides from Lecture07 Chapter 16 Our Star the Sun Chapter Overview The Sun s Surface Atmosphere 16 5 Why the gaseous Sun appears to have a sharp outer edge 16 6 Why the upper regions of the solar atmosphere have an emission spectrum 16 7 The relationship between the Sun s corona and the solar wind 16 8 The nature of sunspots 16 9 The connection between sunspots and the Sun s magnetic field 16 10 How magnetic reconnection can power immense solar eruptions Chapter Overview The Sun s Interior 16 1 The source of the Sun s heat and light 16 2 How scientists model the Sun s internal structure 16 3 How the Sun s vibrations reveal what lies beneath its glowing surface 16 4 How scientists are able to probe the Sun s energy generating core Chapter Overview The Sun s Interior 16 1 The source of the Sun s heat and light 16 2 How scientists model the Sun s internal structure 16 3 How the Sun s vibrations reveal what lies beneath its glowing surface 16 4 How scientists are able to probe the Sun s energy generating core This is the textbook material on which I will focus Chapter Overview The Sun s Interior 16 1 The source of the Sun s heat and light 16 2 How scientists model the Sun s internal structure 16 3 How the Sun s vibrations reveal what lies beneath its glowing surface 16 4 How scientists are able to probe the Sun s energy generating core This is the textbook material on which I will focus but first let s skim through the material in sections 16 5 through 16 10 Figure 16 7 16 5 The Sun s Photosphere Figure 16 9 Granulation of the Photosphere Figure 16 9 Granulation of the Photosphere A high resolution photograph of the Sun s surface reveals a blotchy pattern called granulation Figure 16 9 Granulation of the Photosphere A high resolution photograph of the Sun s surface reveals a blotchy pattern called granulation this is evidence of heat convection the surface is boiling 16 8 Sunspots Figure 16 7 low temperature regions in the photosphere 16 8 Sunspots Figure 16 17 Tracking the Sun s Rotation 16 8 Sunspots Tracking the Sun s Rotation Figure 16 17 The Sun rotates once in about 4 weeks 16 8 Sunspots The Sunspot Cycle Figure 16 18 16 8 Sunspots The Sunspot Cycle Figure 16 18 The number of sunspots on the Sun varies with a period of about 11 years most recent maximum in year 2000 Figure 16 11 16 6 The Sun s Chromosphere 16 7 The Solar Corona Figure 16 13 visible light 16 7 The Solar Corona Figure 16 15 ultraviolet light Figures 16 27 16 28 16 10 Coronal Prominences 16 9 Sun s Magnetic Field The Sun contains a magnetic field with a fairly complex structure Coronal loops see Fig 16 25 and prominences often outline the magnetic field s complex structure Sunspots appear to be associated with regions on the Sun s surface where the magnetic field is especially strong The north and south magnetic poles of the Sun reverse every 11 years 16 9 Sun s Magnetic Field The Sun contains a magnetic field with a fairly complex structure Coronal loops see Fig 16 25 and prominences often outline the magnetic field s complex structure Sunspots appear to be associated with regions on the Sun s surface where the magnetic field is especially strong The north and south magnetic poles of the Sun reverse every 11 years NOTE see 9 4 The Earth s own magnetic field reverses direction on an irregular schedule ranging from tens of thousands to hundreds of thousands of years Relevance to Other Stars If the Sun is a typical star think about how all these surface phenomena may be relevant to our studies of all other stars Intrinsic brightness can be variable Mass of a star may decrease over time Magnetic fields may be important Chapter Overview The Sun s Interior 16 1 The source of the Sun s heat and light 16 2 How scientists model the Sun s internal structure 16 3 How the Sun s vibrations reveal what lies beneath its glowing surface 16 4 How scientists are able to probe the Sun s energy generating core This is the textbook material on which I will focus Figure 16 4 Sun s Internal Structure Modeling the Sun s Interior 1 Hydrostatic Equilibrium 2 Thermal Equilibrium 3 Energy from nuclear fusion E mc 2 Modeling the Sun s Interior Hydrostatic Equilibrium Gas pressure force directed outward balances force of gravity directed inward throughout the interior If not balanced Sun s structure should change appreciably in a matter of hours Modeling the Sun s Interior Hydrostatic Equilibrium Gas pressure force directed outward balances force of gravity directed inward throughout the interior If not balanced Sun s structure should change appreciably in a matter of hours Modeling the Sun s Interior Thermal Equilibrium Sun is steadily losing energy at its surface it s shining it is trying to cool off Heat from the Sun s interior slowly diffuses toward the surface This lost heat can be replenished by slow gravitational contraction whenever a gas is compressed its temperature rises this is referred to as KelvinHelmholtz contraction see 16 1 If Kelvin Helmholtz contraction is responsible for keeping the Sun s interior hot the Sun s structure should change appreciably on a time scale of 10 million years Modeling the Sun s Interior Thermal Equilibrium Sun is steadily losing energy at its surface it s shining it is trying to cool off Heat from the Sun s interior slowly diffuses toward the surface This lost heat can be replenished by slow gravitational contraction whenever a gas is compressed its temperature rises this is referred to as KelvinHelmholtz contraction see 16 1 If Kelvin Helmholtz contraction is responsible for keeping the Sun s interior hot the Sun s structure should change appreciably on a time scale of 10 million years Modeling the Sun s Interior Thermal Equilibrium Sun is steadily losing energy at its surface it s shining it is trying to cool off Heat from the Sun s interior slowly diffuses toward the surface This lost heat can be replenished by slow gravitational contraction whenever a gas is compressed its temperature rises this is referred to as KelvinHelmholtz contraction see 16 1 If Kelvin Helmholtz contraction is responsible for keeping the Sun s interior hot the Sun s structure should change appreciably on a time scale of 10 million years Modeling the Sun s Interior Thermal Equilibrium Sun is steadily losing energy at its surface it s shining it is trying to cool off Heat from the Sun s interior slowly diffuses toward the surface