Solar Theory (MT 4510) Clare E Parnell School of Mathematics and Statistics

Sun Facts kg/m 3 1/4 x Earth’s density kg/m 3 Density 2 x kg x Earth’s mass 6 x kg Mass 1.41 x km x Earth’s volume 1.1 x km 3 Volume km 109 x Earth’s radius km Radius SunEarth

Sun Facts 4 x W 4 x light bulbs Luminosity km x Earth’s radius Distance from Earth 25 days - equator 33 days - poles ‘differential rotation’ 1 day Rotation rate Electrically charged gas (plasma) core: hydrogen Solid core: iron Consistency SunEarth

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

Solar Interior Core (T~1.6x10 7 K) Radiative Zone (T~8x10 6 K) Convection Zone (T~2x10 6 K) Photosphere (surface) (T~6400 K)

Helioseismology 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 mins Strongest periods ~ 5 mins

Solar 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 Atmosphere

Solar Atmosphere Photosphere (6600 K>T> 4300 K) Chromosphere (4300 K<T<10 6 K) Corona (T>10 6 K)

Photosphere T ~ K ρ ~ th of water P ~ th of atmosphere H ~ 100 km Visible light images reveal sunspots Magnetograms reveal surface magnetic fields Field into Sun – black Field out of Sun - white

Chromosphere 4300 K < T < 10 6 K ρ ~ less than water P ~ not much! H ~ 2500 km Observed in many wavelengths, e.g., Ca II K H alpha 304 Å

Corona T > 10 6 K (low corona) ρ < less than water P ~ even less! H - to Earth & beyond! Observed in EUV (T~10 6 K) Soft X-ray (T> 2x10 6 K) Visible (white) light

Coronal Heating Problem

Corona Coronal hole X-ray bright point Active region Coronal loops

Solar Cycle Solar Maximum Solar Minimum

Umbra Penumbra Sunspots Magnetic field strength ~ 2-3x10 3 G Umbra – vertical field Penumbra – horizontal field Number of sunspots varies over 11 year cycle

Prominences Situated in corona Cool, dense plasma confined in vertical sheets Lifetimes: days-months Size: 2x10 5 x 5x10 4 x 6x10 3 km 3 (LxHxW) ρ: kg cm -3 T: 5-10 x10 3 K

Solar Flares Sudden, impulsive, intense, large-scale, heating events Very energetic: from J Lifetimes: hours

Coronal Mass Ejections (CMEs) Very large events that eject mass from the Sun Very large events that eject mass from the Sun Energy: J Energy: J Mass: kg Mass: kg Lifetime: hours Lifetime: hours Usually related to a prominence eruption Usually related to a prominence eruption

Solar Wind Ions and electrons continually stream out along magnetic field lines Ions and electrons continually stream out along magnetic field lines Solar wind: Solar wind: –Strong above poles (open field) –Weak about equator (closed field)

Sun-Earth Connection Solar wind continually buffets Earth’s magnetic field CME’s can disrupt Earth’s magnetic field and cause Auroras

The Sun Today! EIT 304 EIT 171EIT 195EIT 284 LASCO C3 LASCO C2MDI MAGMDI CONT

Solar Theory Course Outline structure of events Maxwell’s equations and magnetic fields 1 Sun/Earth connection Solar wind 6 Helio/coronal-seismology, coronal heating, solar wind MHD waves 5 Coronal arcades and loop structures, prominences MHD equilibria 4 Flares, CMEs, coronal heating, solar wind Magnetic reconnection and magnetic energy 3 Describe behaviour of Sun MHD equations 2ImportanceTopic§

The Sun (Summary)