26 oct 2000astr103, gmu, dr. correll1 ch 9--the sun

26 Oct 2000 ASTR103, GMU, Dr. Correll 1

Ch 9--The SunCh 9--The Sun


What do you think?What do you think?

• What fraction of the solar system’s mass is in the Sun?

• Does the Sun have a solid and liquid interior, like the Earth?

• What is the surface of the Sun like?• Does the Sun rotate?• What makes the Sun shine?


Sun’s Vital StatisticsSun’s Vital Statistics


Solar StructureSolar Structure

• Atmosphere– Photosphere ~ 500 km

thick--main light emitting surface

– Chromosphere ~ 2000 km or more--middle layer giving absorption bands

– Corona ~ 106 km or more--outer layer, very thin, very hot


Photospheric SpectrumPhotospheric Spectrum

• Photospheric absorption spectrum - contains several tens of thousands of absorption lines– Strongest absorption lines due to Ca II– Hydrogen Balmer series fairly prominent– Most absorption lines due to Fe I and Fe II– About 70 of 92 naturally occurring elements observed in

photospheric spectrum– About 20 molecules observed in photospheric spectrum

• Chemical composition can be determined from spectrum and knowledge of temperature and density of photosphere


Photospheric GranulationPhotospheric Granulation

• Photospheric granulation - “rice-grained” pattern of convection cells– Due to magnetic

field bundles


ChromosphereChromosphere

• Chromospheric emission spectrum– Many emission lines matching wavelengths of photospheric

absorption lines– Bright yellow line produced by helium– Chromospheric temperature is up to 30,000 K at highest

level and gas density is lower than photosphere– From this, one concludes that temperature must rise rapidly

up through chromosphere


Chromospheric SpiculesChromospheric Spicules

• Spicules - chromosphere stippled with jet-like spikes of gas– Best seen in red H

spectroheliogram– Dark features, like blades of

grass, outlining interiors of supergranule cells

• Reveals supergranules– spanned by hundreds of

granules


CoronaCorona

• Corona - halo of pale white glowing gas extending several solar radii (several million kilometers) out from photosphere

• Creates a solar wind– millions of tons of H+,

e-, and He++ blown away each second


Corona (cont)Corona (cont)

• Coronal spectrum– All emission lines originate in highly excited ions of

familiar elements• Temperatures in the millions of degrees Kelvin• Example - iron from which as many as 15 electrons

have been stripped in corona's extremely hot, tenuous gaseous

– Densities must be quite low compared to photosphere to produce emission spectrum from gas that is transparent to photospheric radiation


Quiet and Active SunQuiet and Active Sun

• Quiet Sun - average solar conditions devoid of various phenomena which make up solar activity

• Active Sun - cycle of transient activity which includes variety of phenomena– Sunspot groups (chief identifier of 11 cycle of activity)– Flares– Filaments and prominences– Coronal holes, quiet regions, active regions


The Sun’s Magnetic FieldThe Sun’s Magnetic Field

• Global structure throughout solar system



• Local variations throughout surface of sun


Photospheric SunspotsPhotospheric Sunspots

• Sunspots - cooler structures than normal photosphere– Defined by

magnetic field


Solar Activity CycleSolar Activity Cycle

• Sunspot cycle - more than century ago sunspots discovered to come and go in roughly 11 year cycle– Magnitude and period of cycle not exact– Polarity (north or south seeking) of magnetic field reverses

each cycle• 22-year magnetic cycle far more repeatable than 11-year

frequency cycle


Sunspot Cycle - Frequency Sunspot Cycle - Frequency


Chromospheric FlareChromospheric Flare


Soft X-RaySoft X-RayJuly 7, 1998July 7, 1998

Coronal HoleCoronal Hole

Coronal Active Coronal Active RegionRegion

Coronal Quiet Coronal Quiet RegionRegion

EquatorEquator

PolePole

PolePole


Coronal ProminencesCoronal Prominences

• Prominences - Chromospheric material extending upward into corona– Seen against

photospheric or chromospheric disk known as filaments

ProminenceProminence


Coronal Prominences (cont)Coronal Prominences (cont)

• Properties– Much cooler than surrounding corona– Lifetimes up to 90 days


ProminencesProminences


The Sun’s InteriorThe Sun’s Interior


• Thermonuclear fusion - fusion of small mass nuclei to form more massive nuclei with resulting direct conversion of mass into energy by E = mc2

• Nuclear forces (“strong” and “weak”) are much more energetic than chemical forces (“electromagnetic”)

Thermonuclear FusionThermonuclear Fusion


Hydrogen “Burning”Hydrogen “Burning”

Proton-proton chain


Stellar StructureStellar Structure

• Energy Transport– conduction--molecular

collisions– radiation--light waves– convection--fluid flow



• Our Sun– energy generated by

fusion in the core– energy radiates outward

via radiation through the hot interior

– cooler outer layer is “opaque” to the radiation and absorbs the energy

– convection transfers energy outwards to photosphere



• Hydrostatic Equilibrium--balance of gravitational attraction and pressure at all layers of the star



• Equations of stellar structure are solved on computers to give description of stellar interior and energy radiated out into space


Oscillatory MotionsOscillatory Motions

• 1960, vertical oscillatory motions detected in and above solar granulation via Doppler shifted spectra– Typical excursion is on order of 50 to 100 km– Period of oscillations almost exactly 5 minutes with

velocities of about 0.5 km/s– 1984, Sun's closest stellar neighbor, Alpha

Centauri, was also shown to be undergoing 5-minute oscillations


Oscillatory Motions (cont)Oscillatory Motions (cont)

Helioseismology


Source of Stellar EnergySource of Stellar Energy

• Theory & Observations of the sun– Luminosity is known– Nuclear physics well

understood– Predicted central

temperature of sun agrees with helioseismology

– But, neutrino flux about 1/3 too low

C2Cl4 (cleaning fluid) tank in South Dakota


Source of Stellar EnergySource of Stellar Energy

• Superkamiokande--detected different species of massive neutrinos– Neutrinos may change type travelling between Sun and Earth


What do you think?What do you think?

• What fraction of the solar system’s mass is in the Sun?– 99.85%

• Does the Sun have a solid and liquid interior, like the Earth?– No, the Sun is composed entirely of hot gases

• What is the surface of the Sun like?– The photosphere is composed of hot, churning gases

• Does the Sun rotate?– The Sun’s surface rotates differentially, varying between once

every 25 days near its poles and once every 35 days at its equator

• What makes the Sun shine?– Thermonuclear fusion at the Sun’s core is the source of the Sun’s

energy


Questions for ThoughtQuestions for Thought

• Describe the interior layers (structure) of the Sun, how energy is generated, and how the energy makes its way to the outer layers of the Sun to be radiated into space

26 oct 2000astr103, gmu, dr. correll1 ch 9--the sun

Documents

prominentmost absorption

solar systemastr103

solar radii

solar activityactive

absorption bandscorona

solar windmillions of

solar systems mass

gas density