Solar TheorySolar Theory(MT 4510)(MT 4510)

Clare E ParnellClare E ParnellSchool of Mathematics and School of Mathematics and

StatisticsStatistics

Sun FactsSun Facts

1 400 kg/m1 400 kg/m33

1/4 x Earth’s density1/4 x Earth’s density5 500 5 500 kg/mkg/m33

DensitDensityy

2 x 102 x 103030 kg kg

333 000 x Earth’s mass333 000 x Earth’s mass6 x 106 x 102424 kgkg

MassMass

1.41 x1.41 x 10101818 km km33

1 300 000 x Earth’s 1 300 000 x Earth’s volumevolume

1.1 x 101.1 x 101212 kmkm33

VolumVolumee

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 1024 24 light bulbslight bulbsLuminositLuminosityy

149 000 000 km149 000 000 km

23 000 x Earth’s 23 000 x Earth’s radiusradius

Distance 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 Electrically charged gasgas

(plasma) core: (plasma) core: hydrogenhydrogen

Solid core: Solid core: ironiron

ConsistenConsistencycy

SunSunEarthEarth

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

Solar InteriorSolar InteriorCore

(T~1.6x107 K)

Radiative Zone(T~8x106 K)

Convection Zone(T~2x106 K)

Photosphere(surface)

(T~6400 K)

HelioseismologyHelioseismology• 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).

Observing Sun’s Observing Sun’s AtmosphereAtmosphere

Solar AtmosphereSolar Atmosphere

Photosphere(6600 K>T> 4300 K)

Chromosphere(4300 K<T<106 K)

Corona(T>106 K)

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• H alpha• 304 Å

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)• Visible (white) light

Coronal Heating ProblemCoronal Heating Problem

CoronaCoronaCoronal holeX-ray bright point

Active region Coronal loops

Solar CycleSolar Cycle

Solar Maximum

SolarMinimum

Umbra Penumbra

SunspotsSunspots

• Magnetic field strength ~ 2-3x103 G

• Umbra – vertical field

• Penumbra – horizontal field

• Number of sunspots varies over 11 year cycle

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 FlaresSolar Flares• Sudden, impulsive,

intense, large-scale, heating events

• Very energetic: from 1022 - 1025 J

• Lifetimes: hours

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: 101313 kg kg• Lifetime: hoursLifetime: hours• Usually related Usually related

to a prominence to a prominence eruptioneruption

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)

Sun-Earth ConnectionSun-Earth Connection

• Solar wind continually buffets Earth’s magnetic field

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

The Sun Today!The Sun Today!EIT 304 EIT 171 EIT 195 EIT 284

LASCO C3LASCO C2MDI MAGMDI CONT

Solar Theory CourseSolar Theory Course

Outline structure of Outline structure of eventsevents

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

11

Sun/Earth connectionSun/Earth connectionSolar windSolar wind66

Helio/coronal-Helio/coronal-seismology, coronal seismology, coronal heating, solar windheating, solar wind

MHD wavesMHD waves55

Coronal arcades and Coronal arcades and loop structures, loop structures, prominencesprominences

MHD equilibriaMHD equilibria44

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

Magnetic Magnetic reconnection and reconnection and magnetic energymagnetic energy

33Describe behaviour of Describe behaviour of SunSun

MHD equationsMHD equations22

ImportanceImportanceTopicTopic§§

The Sun (Summary)The Sun (Summary)