1. MT4510 Solar Theory Thomas Neukirch

2. Sun Facts Earth Sun Radius 6 400 km 696 000 km 109 x Earth’s radius
Volume
1.1 x 1012 km3
1.41 x 1018 km3
x Earth’s volume
Mass
6 x 1024 kg
2 x 1030 kg
x Earth’s mass
Density
5 500 kg/m3
1 400 kg/m3
1/4 x Earth’s density

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

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

5. Solar Interior Core Radiative Zone Convection Zone Photosphere
(surface)

6. 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

7. 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).

8. Solar Atmosphere
Photosphere
Chromosphere
Corona

9. Observing Sun’s Atmosphere

10. Photosphere 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

11. 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)

12. 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> 2x106 K)
White light

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

14. Coronal Heating Problem

15. Solar Cycle
Solar Maximum
Solar
Minimum

16. Sunspots Magnetic field strength ~ 2-3x103 G
Umbra
Penumbra
Magnetic field strength ~ 2-3x103 G
Umbra – (almost) vertical field
Penumbra – (more) horizontal field
Number of sunspots varies over 11 year cycle

17. 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)

18. Prominences Situated in corona
Cool, dense plasma confined in vertical sheets
Lifetimes: days-months
Size: 2x105 x 5x104 x 6x103 km3 (LxHxW)
ρ: kg cm-3
T: 5-10 x103 K

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

20. 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

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

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

23. The Sun on 10 Feb 2008 EIT 304 EIT 171 EIT 195 EIT 284 MDI CONT
MDI MAG
LASCO C2
LASCO C3

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

25. The Sun (Summary)