MT4510MT4510Solar TheorySolar Theory

Thomas NeukirchThomas Neukirch

Sun FactsSun Facts

1 400 kg/m1 400 kg/m33

1/4 x Earth’s density1/4 x Earth’s density5 500 kg/m5 500 kg/m33DensityDensity

2 x 102 x 103030 kg kg

333 000 x Earth’s mass333 000 x Earth’s mass6 x 106 x 102424 kg kgMassMass

1.41 x1.41 x 10101818 km km33

1 300 000 x Earth’s volume1 300 000 x Earth’s volume1.1 x 101.1 x 101212 kmkm33

VolumeVolume

696 000 km696 000 km

109 x Earth’s radius109 x Earth’s radius66 400400 kmkmRadiusRadius

SunSunEarthEarth

Sun FactsSun Facts

4 x 104 x 1026 26 WW

4 x 104 x 1025 25 light bulbslight bulbsLuminositLuminosityy

149 000 000 km149 000 000 km

23 000 x Earth’s radius23 000 x Earth’s radiusDistance Distance from Earthfrom Earth

25 days - equator25 days - equator

33 days - poles33 days - poles

‘‘differential rotation’differential rotation’

1 day1 dayRotation Rotation raterate

Electrically charged gasElectrically charged gas

core: hydrogencore: hydrogenSolid Solid

core: ironcore: ironConsistenConsistencycy

SunSunEarthEarth

Sun’s Nuclear CoreSun’s Nuclear Core• Fusion of hydrogen in core produces gamma rays

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Solar InteriorSolar Interior

Core

Radiative Zone

Convection Zone

Photosphere(surface)

HelioseimologyHelioseimology• Used to study the interior of the Sun

• It is the study of resonant wave modes of oscillation of the Sun

• Modes of oscillation are visible manifestations of trapped standing sound waves

• Strongest periods ~ 5 Strongest periods ~ 5 minsmins

Solar Rotation RateSolar Rotation Rate• Relative rotation rates of material in the Sun - determined using helioseismology

• Red material – fastest

• Dark blue – slowest

• Interior: red moves ~ 4% faster than outer layers.

• Surface: red (equator) moves ~ 3,000 mph faster than blue (poles).

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Solar AtmosphereSolar Atmosphere

Photosphere

Chromosphere

Corona

Observing Sun’s Observing Sun’s AtmosphereAtmosphere

PhotospherePhotosphere• T ~ 6600-4300 K• ρ ~ 10-8th of water• P ~ 10-2th of atmosphere• H ~ 100 km

• Visible light images reveal sunspots• Magnetograms reveal

surface magnetic fields• Field into Sun – black• Field out of Sun - white

ChromosphereChromosphere

• 4300 K < T < 106 K• ρ ~ 10-8-10-14 less

than water• P ~ not much!• H ~ 2500 km

• Observed in many wavelengths, e.g.,• Ca II K (393.3 nm)• H alpha (656.3 nm)

CoronaCorona• T > 106 K (low corona)• ρ < 10-14 less than

water• P ~ even less!• H - to Earth & beyond!

• Observed in• EUV (T~106 K)• Soft X-ray (T> 2x106 K)• White light

CoronaCoronaCoronal holeX-ray bright point

Active region Coronal loops

Coronal Heating ProblemCoronal Heating Problem

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Solar Maximum

SolarMinimum

Solar CycleSolar Cycle

Umbra Penumbra

SunspotsSunspots

• Magnetic field strength ~ 2-3x103 G

• Umbra – (almost) vertical field

• Penumbra – (more) horizontal field

• Number of sunspots varies over 11 year cycle

Magnetic field responsible Magnetic field responsible for solar activity !for solar activity !

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Sunspots = strong magnetic field

Emission in all wavelengths correlates well with strong magnetic field regions

Magnetic field dominates solar atmosphere

(magnetic energy density >> pressure)

ProminencesProminences

• Situated in corona• Cool, dense plasma

confined in vertical sheets

• Lifetimes: days-months

• Size: 2x105 x 5x104 x 6x103 km3 (LxHxW)

• ρ: 10-12 kg cm-3

• T: 5-10 x103 K

Solar Flares Solar Flares

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• Sudden, impulsive, intense, large-scale, heating events

• Very energetic: from 1022 - 1025 J

• Lifetimes: hours

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Coronal Mass Ejections Coronal Mass Ejections (CMEs)(CMEs)• Very large Very large

events that eject events that eject mass from the mass from the SunSun

• Energy: 10Energy: 102525 J J• Mass: 10Mass: 101515 kg kg• Lifetime: hoursLifetime: hours• Usually related Usually related

to a prominence to a prominence eruptioneruption

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Solar WindSolar Wind

• Ions and electrons Ions and electrons continually stream continually stream out along magnetic out along magnetic field linesfield lines

• Solar wind:Solar wind:– Strong above poles Strong above poles

(open field)(open field)– Weak about equator Weak about equator

(closed field)(closed field)

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Sun-Earth ConnectionSun-Earth Connection

• Solar wind continually buffets Earth’s magnetic field

• CME’s can distort Earth’s magnetic field and cause Auroras

The Sun on 10 Feb 2008The Sun on 10 Feb 2008EIT 304 EIT 171 EIT 195 EIT 284

LASCO C3LASCO C2MDI MAGMDI CONT

Solar Theory CourseSolar Theory Course§§ TopicTopic ImportanceImportance

11 Maxwell’s equations Maxwell’s equations and magnetic fieldsand magnetic fields

Outline structure of Outline structure of eventsevents

22 MHD equationsMHD equations Describe behaviour of Describe behaviour of SunSun

33 Magnetic Magnetic reconnection and reconnection and magnetic energymagnetic energy

Flares, CMEs, coronal Flares, CMEs, coronal heating, solar windheating, solar wind

44 MHD equilibriaMHD equilibria Coronal arcades and Coronal arcades and loop structures, loop structures, prominencesprominences

55 MHD wavesMHD waves Helio/coronal-Helio/coronal-seismology, coronal seismology, coronal heating, solar windheating, solar wind

66 Solar windSolar wind Sun/Earth connectionSun/Earth connection

The Sun (Summary)The Sun (Summary)