1. 26 Oct 2000ASTR103, GMU, Dr. Correll1 Ch 9--The Sun

2. 26 Oct 2000ASTR103, GMU, Dr. Correll2 What do you think? What fraction of the solar system’s mass is in the Sun? Does the Sun have a solid and liquid interior, like the Earth? What is the surface of the Sun like? Does the Sun rotate? What makes the Sun shine?

3. 26 Oct 2000ASTR103, GMU, Dr. Correll3 Sun’s Vital Statistics

4. 26 Oct 2000ASTR103, GMU, Dr. Correll4 Solar Structure Atmosphere –Photosphere ~ 500 km thick--main light emitting surface –Chromosphere ~ 2000 km or more--middle layer giving absorption bands –Corona ~ 10 6 km or more--outer layer, very thin, very hot

5. 26 Oct 2000ASTR103, GMU, Dr. Correll5 Photospheric Spectrum Photospheric absorption spectrum - contains several tens of thousands of absorption lines –Strongest absorption lines due to Ca II –Hydrogen Balmer series fairly prominent –Most absorption lines due to Fe I and Fe II –About 70 of 92 naturally occurring elements observed in photospheric spectrum –About 20 molecules observed in photospheric spectrum Chemical composition can be determined from spectrum and knowledge of temperature and density of photosphere

6. 26 Oct 2000ASTR103, GMU, Dr. Correll6 Photospheric Granulation Photospheric granulation - “rice- grained” pattern of convection cells –Due to magnetic field bundles

7. 26 Oct 2000ASTR103, GMU, Dr. Correll7 Chromosphere Chromospheric emission spectrum –Many emission lines matching wavelengths of photospheric absorption lines –Bright yellow line produced by helium –Chromospheric temperature is up to 30,000 K at highest level and gas density is lower than photosphere –From this, one concludes that temperature must rise rapidly up through chromosphere

8. 26 Oct 2000ASTR103, GMU, Dr. Correll8 Chromospheric Spicules Spicules - chromosphere stippled with jet-like spikes of gas –Best seen in red H  spectroheliogram –Dark features, like blades of grass, outlining interiors of supergranule cells Reveals supergranules –spanned by hundreds of granules

9. 26 Oct 2000ASTR103, GMU, Dr. Correll9 Corona Corona - halo of pale white glowing gas extending several solar radii (several million kilometers) out from photosphere Creates a solar wind –millions of tons of H +, e -, and He ++ blown away each second

10. 26 Oct 2000ASTR103, GMU, Dr. Correll10 Corona (cont) Coronal spectrum –All emission lines originate in highly excited ions of familiar elements Temperatures in the millions of degrees Kelvin Example - iron from which as many as 15 electrons have been stripped in corona's extremely hot, tenuous gaseous –Densities must be quite low compared to photosphere to produce emission spectrum from gas that is transparent to photospheric radiation

11. 26 Oct 2000ASTR103, GMU, Dr. Correll11 Quiet and Active Sun Quiet Sun - average solar conditions devoid of various phenomena which make up solar activity Active Sun - cycle of transient activity which includes variety of phenomena –Sunspot groups (chief identifier of 11 cycle of activity) –Flares –Filaments and prominences –Coronal holes, quiet regions, active regions

12. 26 Oct 2000ASTR103, GMU, Dr. Correll12 The Sun’s Magnetic Field Global structure throughout solar system

13. 26 Oct 2000ASTR103, GMU, Dr. Correll13 The Sun’s Magnetic Field Local variations throughout surface of sun

14. 26 Oct 2000ASTR103, GMU, Dr. Correll14 The Sun’s Magnetic Field

15. 26 Oct 2000ASTR103, GMU, Dr. Correll15 Photospheric Sunspots Sunspots - cooler structures than normal photosphere –Defined by magnetic field

16. 26 Oct 2000ASTR103, GMU, Dr. Correll16 Solar Activity Cycle Sunspot cycle - more than century ago sunspots discovered to come and go in roughly 11 year cycle –Magnitude and period of cycle not exact –Polarity (north or south seeking) of magnetic field reverses each cycle 22-year magnetic cycle far more repeatable than 11-year frequency cycle

17. 26 Oct 2000ASTR103, GMU, Dr. Correll17 Sunspot Cycle - Frequency

18. 26 Oct 2000ASTR103, GMU, Dr. Correll18 Chromospheric Flare

19. 26 Oct 2000ASTR103, GMU, Dr. Correll19 Soft X-Ray July 7, 1998 Coronal Hole Coronal Active Region Coronal Quiet Region Equator Pole Pole

20. 26 Oct 2000ASTR103, GMU, Dr. Correll20 Coronal Prominences Prominences - Chromospheric material extending upward into corona –Seen against photospheric or chromospheric disk known as filaments Prominence

21. 26 Oct 2000ASTR103, GMU, Dr. Correll21 Coronal Prominences (cont) Properties –Much cooler than surrounding corona –Lifetimes up to 90 days

22. 26 Oct 2000ASTR103, GMU, Dr. Correll22 Prominences

23. 26 Oct 2000ASTR103, GMU, Dr. Correll23 The Sun’s Interior

24. 26 Oct 2000ASTR103, GMU, Dr. Correll24 Thermonuclear fusion - fusion of small mass nuclei to form more massive nuclei with resulting direct conversion of mass into energy by E = mc 2 Nuclear forces (“strong” and “weak”) are much more energetic than chemical forces (“electromagnetic”) Thermonuclear Fusion

25. 26 Oct 2000ASTR103, GMU, Dr. Correll25 Hydrogen “Burning” Proton-proton chain

26. 26 Oct 2000ASTR103, GMU, Dr. Correll26 Stellar Structure Energy Transport –conduction--molecular collisions –radiation--light waves –convection--fluid flow

27. 26 Oct 2000ASTR103, GMU, Dr. Correll27 Stellar Structure Our Sun –energy generated by fusion in the core –energy radiates outward via radiation through the hot interior –cooler outer layer is “opaque” to the radiation and absorbs the energy –convection transfers energy outwards to photosphere

28. 26 Oct 2000ASTR103, GMU, Dr. Correll28 Stellar Structure Hydrostatic Equilibrium-- balance of gravitational attraction and pressure at all layers of the star

29. 26 Oct 2000ASTR103, GMU, Dr. Correll29 Stellar Structure Equations of stellar structure are solved on computers to give description of stellar interior and energy radiated out into space

30. 26 Oct 2000ASTR103, GMU, Dr. Correll30 Oscillatory Motions 1960, vertical oscillatory motions detected in and above solar granulation via Doppler shifted spectra –Typical excursion is on order of 50 to 100 km –Period of oscillations almost exactly 5 minutes with velocities of about 0.5 km/s –1984, Sun's closest stellar neighbor, Alpha Centauri, was also shown to be undergoing 5- minute oscillations

31. 26 Oct 2000ASTR103, GMU, Dr. Correll31 Oscillatory Motions (cont) Helioseismology

32. 26 Oct 2000ASTR103, GMU, Dr. Correll32 Source of Stellar Energy Theory & Observations of the sun –Luminosity is known –Nuclear physics well understood –Predicted central temperature of sun agrees with helioseismology –But, neutrino flux about 1/3 too low C 2 Cl 4 (cleaning fluid) tank in South Dakota

33. 26 Oct 2000ASTR103, GMU, Dr. Correll33 Source of Stellar Energy Superkamiokande--detected different species of massive neutrinos –Neutrinos may change type travelling between Sun and Earth

34. 26 Oct 2000ASTR103, GMU, Dr. Correll34 What do you think? What fraction of the solar system’s mass is in the Sun? –99.85% Does the Sun have a solid and liquid interior, like the Earth? –No, the Sun is composed entirely of hot gases What is the surface of the Sun like? –The photosphere is composed of hot, churning gases Does the Sun rotate? –The Sun’s surface rotates differentially, varying between once every 25 days near its poles and once every 35 days at its equator What makes the Sun shine? –Thermonuclear fusion at the Sun’s core is the source of the Sun’s energy

35. 26 Oct 2000ASTR103, GMU, Dr. Correll35 Questions for Thought Describe the interior layers (structure) of the Sun, how energy is generated, and how the energy makes its way to the outer layers of the Sun to be radiated into space