Understanding the Sun: Key Facts and Theories

1. MT4510Solar TheoryThomas Neukirch

2. Sun Facts Earth Sun Radius 6400km 696 000 km 109 x Earth’s radius Volume 1.1 x 1012 km3 1.41 x1018 km3 1 300 000 x Earth’s volume Mass 6 x 1024 kg 2 x 1030 kg 333 000 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 149 000 000 km 23 000 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 Minimum Solar Maximum Solar Cycle

16. Penumbra Umbra Sunspots • 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: 10-12 kg cm-3 • T: 5-10 x103 K

19. Solar Flares • Sudden, impulsive, intense, large-scale, heating events • Very energetic: from 1022 - 1025 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

25. The Sun (Summary)