NASA's Solar Dynamics Observatory: Exploring Extreme Ultraviolet Wavelengths

1. Phys 1830: Lecture 27 NASA’s Solar Dynamics Observatory: Extreme UltraViolet wavelengths New password. • Previous Classes: • Exoplanets • This Class • The Sun • Upcoming Classes • Stars • Luminosity • Radii, Mass • Lifetime • Stellar Populations Inverted, false colour H_alpha image. Alan Friedman.

2. The Sun • The photosphere is the visible "surface" of the Sun. • Below it lie the convection zone, the radiation zone, and the core. • Above the photosphere, the solar atmosphere consists of the chromosphere, the transition zone, and the corona

3. The Sun’s Interior • Stars like our sun are in hydrostatic equilibrium. • Stable balance between the opposing forces of gravity and pressure from hot gas. • How is the gas heated?

4. The Sun’s Core • Only one known energy generating mechanism can account for the Sun’s enormous energy output: Thermonuclear Fusion • Requires high temperature (~15 million K)  “thermo” • Fuse H nuclei into Helium nuclei in a nuclear reaction converting a tiny amount of mass into energy.  “nuclear”, “fusion”

5. The Sun’s Core • The thermonuclear reaction in the core is the Proton-Proton Chain • produces anti-matter which annihilates with normal matter generating energy (gamma-rays) • also generates neutrinos (detections at Sudbury Neutrino Observatory confirm this scenario). • Enough H in core to have burned for 4.5 billion years to date and can continue for another 5-6 billion years.

6. Figure 16-9Astronomy Today The Sun’s Interior: Transportation of Energy Outwards Radiation Zone: Ionized state. Energy from core causes separation of electrons from protons which generates photons which are absorbed by atoms. The separation and creation plus absorption of photons repeats. Convection Zone: Excited state.Temperature has dropped so electrons recombine with atoms and photons absorbed. This zone is opaque since photons are not escaping. Photosphere: Less dense so photons can escape. Radiation again.

7. Figure 16-9Astronomy Today The Sun’s Interior: Transportation of Energy Outwards • Neutrinos can escape from the core within minutes. • Photons are absorbed and re-emitted repeatedly. It takes about 170,000 years for a photon to escape according to different estimates.

8. Question 3 1) gravity balances forces from pressure. 2) the rate of fusion equals the rate of fission. 3) radiation and convection balance. 4) mass is converted into energy. 5) fusion doesn’t depend on temperature. The Sun is stable as a star because

9. Question 1 1) core 2) corona 3) photosphere 4) chromosphere 5) convection zone The visible light we see from our Sun comes from which part?

10. The Sun’s Surface Figure 16-10Solar Granulation of the Photosphere

11. The Sun’s Surface KIS/SVST (La Palma) • The sizes of the granules range from approx. 250 km to more than 2000 km, with an average diameter of 1300 km. (height MB = 1225 km; width southern MB ~ 450 km) • Lifetimes of granules typically range from 8 to 15 minutes. (This is a sped up 35min movie.) • Horizontal and vertical velocities of the gas motion are 1 to 2 km/s.

12. Table 16-1The Standard Solar Model As expected, the core where energy is produced is hot and then the sun cools with distance from this engine. Unexpectedly the atmospheric temperature increases with distance! Probably caused by disturbances in the Sun’s magnetic field.

13. The Sun • The photosphere is the visible "surface" of the Sun. • Below it lie the convection zone, the radiation zone, and the core. • Above the photosphere, the solar atmosphere consists of the chromosphere, the transition zone, and the corona

14. Upper Chromosphere Same day at optical wavelengths.. • UV at 304 angstroms. • 60,000 C. • Notice how some of the activity in the atmosphere is correlated with the sunspots.

15. SDO – 2 instruments & many filters  stellar components

16. UV of Corona 171A Lower Corona 1 million K 195A Higher in Corona 1.5 million K 284A Upper Corona 3 million K

17. Activity in the Atmosphere is Related to Sunspots on Photosphere.

18. Sunspots Helioseismology --> depth • Dark because they are a cooler temperature (4500K) compared to surrounding photosphere (5800K). • Spectra  magnetic field is 1000x photosphere. • Sunspots’ magnetic field interfere with the normal flow of hot gas towards the surface  cooler sunspot.

19. Sunspots: Differential Rotation • By observing sunspots • gas at the equator rotates once in about 25 days. • Gas at poles rotates once in about 30 days.

20. Sunspots TRACE satellite • Sunspots are in pairs, linked by magnetic field lines emerging from one and re-entering the sun in the other. • Superheated gas (plasma) flows along the magnetic field lines forming loops in the Far UV image (bottom right).

21. Spicules • Magnetic field tubes filled with gas jetting into chromosphere. • Associated with active regions, such as the sunspot on the left. • Probably due to churning in Sun’s outer layers. • http://antwrp.gsfc.nasa.gov/apod/ap101102.html

22. Solar Dynamics Observatory • Solar “rain” traces B field lines.

23. Generating Sunspots SOHO/ESA/NASA • Twisting in the global magnetic field is caused by • differential rotation with latitude. • Convection of the magnetized gas. Dynamo

24. Sunspot Cycle • This cycle of the magnetic field wrapping, unwrapping and starting to wrap again takes roughly 11 years.