Lec1 082107 Intro

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The Physics of the Sun: 

The Physics of the Sun Course webpage http://www.lpl.arizona.edu/grad/classes/fall2007/Giacalone_537

Slide3: 

The largest flare seen since the National Oceanic and Atmospheric Administration (NOAA) began recording them in 1976 An x-ray image of the Sun (SoHO)

Slide4: 

Artists depiction of a large asteroid striking the Earth (which occur, on average, about 1 every 100 million years) Flare Energy ~ 5x1032 ergs Asteroid Energy ~ 5x1030 ergs 100 times less than a flare! A Fact About Huge Solar Flares (slightly smaller ones occur, on average, about 3 times per day during solar max)

Why Study the Sun ?: 

Why Study the Sun ? Influence on Earth Important for Astronomy/Planetary Sciences Only star that we can see closely The source of many interesting and important physics problems Many interesting research projects For me? Many basic properties are a mystery Understanding the space radiation environment, space weather, acceleration of high-energy charged particles Inti, The Inca Sun God

Topics covered in this course: 

Topics covered in this course Weeks 1-5: Selected Topics in Solar Physics Weeks 6-12: Solar MHD Weeks 13-17: Shocks, CMES, and Solar-Energetic Particles

Topics covered in this course: 

Topics covered in this course Weeks 1-5: Selected Topics in Solar Physics Solar Interior: The Standard Solar Model Basic equations Convection instability Mixing length theory Granulation and Rayleigh-Benard convection Solar Interior: Helioseismology 2 lectures by Frank Hill of NSO Radiative Transfer Basic equations Eddington-Barbier relation, and limb darkening Transfer in lines

Topics covered in this course: 

Topics covered in this course Weeks 1-5: Selected Topics in Solar Physics Weeks 6-12: Solar MHD Basic equations and concepts Photosphere (β >> 1 or gas-motion dominated) Solar Dynamo Corona (β << 1 or magnetic-field dominated) Solar wind Origin, heating and dynamics Solar Wind dragged into space Magnetic Reconnection

Topics covered in this course: 

Topics covered in this course Weeks 1-5: Selected Topics in Solar Physics Weeks 6-12: Solar MHD Weeks 13-17: Shocks, CMEs, and Solar-Energetic Particles Waves and Shocks Flares, CMEs, and blast waves Energetic charged particles Single-particle motion and emission Diffusion Drifts Acceleration

Source of the Sun’s Internal Energy: p-p chain is dominate for the Sun; also CNO chain : 

Source of the Sun’s Internal Energy: p-p chain is dominate for the Sun; also CNO chain Neutrinos are our only direct measurement of the solar interior

Solar Structure: The Standard Solar Model: 

Solar Structure: The Standard Solar Model Theoretical model used to determine the physical properties of the Sun’s interior Hydrostatic and thermal equilibrium A big ball of gas held together by gravity + radiative diffusion Can add convection, but this is difficult (simple approach – mixing-length theory) Nuclear reaction rates and opacities are needed Boundary conditions are tricky – need to use an iterative approach

The Structure of the Sun’s interior: 

The Structure of the Sun’s interior Hydrogen fusion takes place in a core extending from the Sun’s center to about 0.25 solar radius The radiative zone extends from the edge of the core to about 0.71 solar radius Here energy travels outward through radiative diffusion The convective zone is the next layer and is a rather opaque gas Here energy travels outward primarily through convection

Solar Oscillations: 

Solar Oscillations Waves can propagate through the Sun causing a variety of vibrations Like sound waves These are used to infer pressures, densities, chemical compositions, and rotation rates within the Sun Helioseismology

Slide15: 

The tachocline is the interface between the rigidly-rotating radiative zone and the differentially rotating convective zone The tachocline is suprisingly thin: only about 5% of the solar radius. Possibly the source of magnetic flux tubes which permeate the surface (i.e. sunspots).

These variations result from the way magnetic fields are generated within the interior of the Sun: The Solar Dynamo: 

These variations result from the way magnetic fields are generated within the interior of the Sun: The Solar Dynamo

Slide17: 

The convection zone is just outside the radiative zone turbulent convective motions cause overturning (bubbling) motions inside the Sun. These are responsible for the granulation pattern seen on the Sun’s surface. Rayleigh-Bénard convection Radiative zone

Slide18: 

High-resolution images of photospheric granulation

Sunspots: 

Sunspots Existence known since 350 BC (Greece), 28 BC (China) Lower temperature Umbra and penumbra Associated with Intense magnetic fields Zeeman effect (Weiss et al., 2004)

Slide20: 

The Solar Photosphere The visible “surface” of the Sun seen in white light Notice the darkening of the limb

Emission Spectra in the UV: 

Emission Spectra in the UV Far UV To the far right of this plot is the extreme UV (soft X-ray) Near UV Dupree et al., ApJ, 1973

SOHO/EIT image at 195 Angstroms (FeXII): 

SOHO/EIT image at 195 Angstroms (FeXII)

SOHO/EIT movie of the “Halloween” Solar Storms of 2003: 

SOHO/EIT movie of the “Halloween” Solar Storms of 2003

Slide28: 

SOLAR CORONA – SEEN DURING A TOTAL ECLIPSE Magnetism is the Key to Understanding the Sun !

SOHO/LASCO (C3) movie of the “Halloween” Solar Storms of 2003: 

SOHO/LASCO (C3) movie of the “Halloween” Solar Storms of 2003

In-Situ Particle Observations at 1AU of the 2004 Halloween Flares: 

In-Situ Particle Observations at 1AU of the 2004 Halloween Flares Courtesy C. Cohen ACE/SIS data

Slide31: 

The solar wind carves out a cavern in the local interstellar medium – the heliosphere

How does the Sun Influence Earth?: 

How does the Sun Influence Earth? Provides the energy that creates life, warms the planet, drives the dynamic atmosphere and oceans Sun-climate connection? What is the Sun’s role in global warming? 11-year cycles in mammal populations? Geomagnetic storms Aurora Power-grid failures (Canada, 1989); Telecommunications failures Confused homing pigeons? High-energy solar particles can destroy ozone large radiation dosages for astronauts and passengers/pilots on polar air-travel routes

Slide33: 

We have shown how active the Sun can be, but it is not always like this It varies with an 11-year cycle called “the solar cycle” Currently, we are near the minimum in the solar cycle

The number of sunspots at the peak in the 11-year cycle is variable: 

The number of sunspots at the peak in the 11-year cycle is variable The Maunder Minimum was a period from 1645-1715 in which very few sunspots were recorded About 50 during this period compared to ~50,000 over a similar time interval in the 1900’s During the Maunder minimum, there was a period of extremely cold winters in northern Europe The “Little Ice Age” Other cycles and climatic changes have been recorded using proxy records (tree rings, ice cores, riverbed sediments)

The Sun’s role in Global Warming: 

The Sun’s role in Global Warming The Sun is more active in recent cycles, than in the past This increased activity contributes to warming the Earth However, the largest contributor to global warming is the increase in man-made green house gases

Slide36: 

The Sun is slightly dimmer during sunspot minimum as seen by recent, highly sensitive (but not inter-calibrated!) measurements ↑ ↑ Sunspot Minimum Sunspot Minimum Solar Energy arriving at Earth’s orbit “The Solar Constant”

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