MT 4510 Solar Theory Thomas Neukirch Sun Facts

MT 4510 Solar Theory Thomas Neukirch

Sun Facts Radius Volume Mass Density Earth 6 400 km Sun 696 000 km 109 x Earth’s radius 1. 1 x 1012 km 3 1. 41 x 1018 km 3 1 300 000 x Earth’s volume 6 x 1024 kg 2 x 1030 kg 333 000 x Earth’s mass 5 500 kg/m 3 1 400 kg/m 3 1/4 x Earth’s density

Sun Facts Earth Consistency Solid core: iron Rotation 1 day rate Distance from Earth Luminosity Sun Electrically charged gas core: hydrogen 25 days - equator 33 days - poles ‘differential rotation’ 149 000 km 23 000 x Earth’s radius 4 x 1026 W 4 x 1025 light bulbs

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

Solar Interior Core Radiative Zone Convection Zone Photosphere (surface)

Helioseimology • 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

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).

Solar Atmosphere Photosphere Chromosphere Corona

Observing Sun’s Atmosphere

Photosphere • T ~ 6600 -4300 K • ρ ~ 10 -8 th of water • P ~ 10 -2 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 < 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)

Corona 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> 2 x 106 K) • White light

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

Coronal Heating Problem

Solar Cycle Solar Minimum Solar Maximum

Sunspots • Magnetic field strength ~ 2 -3 x 103 G • Umbra – (almost) vertical field • Penumbra – (more) horizontal field • Number of sunspots varies over 11 year cycle Umbra Penumbra

Magnetic field responsible for solar activity ! Sunspots = strong magnetic field Emission in all wavelengths correlates well with strong magnetic field regions Magnetic field dominates solar atmosphere (magnetic energy density >> pressure)

Prominences • Situated in corona • Cool, dense plasma confined in vertical sheets • Lifetimes: days-months • Size: 2 x 105 x 5 x 104 x 6 x 103 km 3 (Lx. Hx. W) • ρ: 10 -12 kg cm-3 • T: 5 -10 x 103 K

Solar Flares • Sudden, impulsive, intense, large-scale, heating events • Very energetic: from 1022 - 1025 J • Lifetimes: hours

Coronal Mass Ejections (CMEs) • Very large events • • that eject mass from the Sun Energy: 1025 J Mass: 1015 kg Lifetime: hours Usually related to a prominence eruption

Solar Wind • Ions and electrons • continually stream out along magnetic field lines 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 distort Earth’s magnetic field and cause Auroras

The Sun on 10 Feb 2008 EIT 304 EIT 171 EIT 195 EIT 284 MDI CONT MDI MAG LASCO C 2 LASCO C 3

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

The Sun (Summary)