A100 The Sun

1. A100 The Sun • Homework and Quiz 9 Today • Reading for next week on Oncourse Today’sAPOD The Sun Today

2. Reading for next week available from the Resource Tool on Oncourse

3. Quiz 9 – Question 1: The diameter of the Sun is about how large compared to the diameter of the Earth? • Twice as big • One half as big • 10 times as big • 100 times as big • 10,000 times as big

4. Question 2: The Sun is supported against the crushing force of its own gravity by • Magnetic forces • Its rapid rotation • The force exerted by escaping neutrinos • Gas pressure • A solid, crystalline ball of metallic hydrogen that fills the interior of the Sun

5. What we covered on Wednesday: • Internal structure of the Sun • Composition of the Sun • Source of the Sun’s energy • The Sun’s lifetime • Balancing pressure, gravity, and temperature • Helioseismology • What neutrinos tell us about the Sun Today: The Sun’s Atmosphere

6. Recall the structure of the Sun…

7. Corona The Sun’s Atmosphere: Photosphere, Chromosphere, Corona, Solar Wind

9. Photosphere The Sun Chromosphere Corona Penumbra Active regions • three layers of the Sun’s atmosphere • photosphere • chromosphere • corona Sunspots Umbra

10. Photosphere Convection Granulation Supergranules Penumbra Active regions Sunspots Prominence Umbra Limb darkening: …when we look near the Sun’s limb we do not see as deeply into the photosphere Limb Limb darkening

11. Photosphere • The photosphere is opaque to visible light • The density is only 1% the density of air • Temperature decreases from inside the Sun to a minimum of 4400K just above the photosphere

12. The Solar Photosphere – the layer we see convection cells ~ 1000 km (600 mi) GRANULATION The difference in T from center to edge is about 300 K > hot gas from lower levels rises upward, cools off, and falls back into the Sun Cells form and disappear in few minutes.

13. Supergranules 35,000 km in diameter The convection moves at 1400 km/h =900 mi/h Supergranules last about a day

14. Question 3: The Sun produces its energy from • Fusion of neutrinos into helium • Fusion of positrons into helium • Disintegration (fission) of helium into hydrogen • Fusion of hydrogen into helium • Electric currents generated in the core

15. Solar Atmosphere • Absorption lines from the photosphere and chromosphere • 67 different elements in various stages of excitation and ionization • The spectrum gives us a picture of the physical conditions in the solar atmosphere

16. Penumbra Umbra Blotchy sunspots appear on the Sun’s “surface” Sunspot grouping Note also the “granulation” resulting from convection under the surface

17. Sunspots are low-temperature regions inthe Sun’s photosphere Sometimes they are isolated but frequently in sunspost groups ~ diameter of Earth (lasting between hours or months)

18. T (umbra) = 4300 K T (penumbra) = 5000 K T (photosphere = 5800 K Photosphere The brightness depends on the 4th power of the temperature (energy flux  T4 )

19. The number of sunspots varies in an 11 year cycle

20. Question 4: Why are sunspots darker than their surroundings? • They are cool relative to the gas around them • They contain 10 times as much iron as surrounding regions • Nuclear reactions occur in them more slowly than in the surrounding gas • Clouds in the corona block our view of the hot photosphere • The gas within them is too hot to emit any light

21. Chromosphere Magnetic Carpet Spicules Above the photosphere, the temperature increases again from 4400 K to 25,000 K at the top of the chromosphere Prominence

22. The chromosphere is characterized by spikes of rising gas (Using Hydrogen filter) • Above the photosphere, the gas density is much lower (10-4 less than the photosphere) but gas is much warmer (25,000 K) • Red color from the emission line of hot hydrogen

23. dense jets of gas that shoot up from the chromosphere Spicules: jets of rising gas Spicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules • Spicules last about 15 minutes • they rise at speeds of 20km/s • 300,000 spicules cover the Sun at any one time

24. Corona Coronal Mass Ejection • The corona, the outermost layer of the solar atmosphere, is made of very high-temperature gases at extremely low density • The solar corona blends into the solar wind at great distances from the Sun Solar Wind Coronal Holes Aurora

25. CORONA a million times fainter than the photosphere... The corona extends for millions of kilometers out from the Sun

26. In the narrow region between the chromosphere and the corona, the temperature rises abruptly to more than a million degrees! (BUT NOT MUCH HEAT!)

27. Activity in the corona includes coronal mass ejections and coronal holes

28. The Sun also produces huge flares that burst into space • A solar flare is a brief eruption of hot, ionized gases from a sunspot group • A coronal mass ejection is a much larger eruption that involves immense amounts of gas from the corona

30. The Solar Wind Coronal particles (mostly electrons and protons) are thrown with such velocity that they cannot be held by the Sun’s gravity • The Sun is “evaporating” constantly (ONLY 0.1% of its mass since its formation) • Interact with objects in the solar system • Earth: cause aurorae • Comets: produces tails • Interacts with edge of solar system: heliopause • Radiation reach Earth in 8 min, particles take a few days (v= 500 km/s)

31. Photosphere Corona The Sun Convection Chromosphere Coronal Mass Ejection Granulation Supergranules Magnetic Carpet Penumbra Active regions Spicules Sunspots Prominence Umbra Solar Wind Limb Coronal Holes Limb darkening Aurora

32. coronal hole The X-ray Sun What causes all this violent activity on the Sun????? mass ejection Rotation and Magnetic Fields!

33. Sunspots show the Sun is rotating(Galileo!) The Sun does not rotate rigidly: the equatorial regions rotate faster (25 days) than the poles (36 days) --- Differential Rotation

34. The Sun rotates at different rates at different solar latitudes Ppole=36 days Pequator=25 days

35. The Sun’s differential rotation winds up the Sun’s magnetic field, storing energy • When the magnetic field suddenly unwinds, that energy is released

36. The Solar Magnetic Field The differential rotation “wraps up” the magnetic field of the Sun Sunspots and other solar activity are caused by the twisted magnetic field of the Sun

37. Solar Activity Varies in an Eleven Year Cycle • The Sun’s magnetic field takes 11 years to twist up and then reestablish itself • The number of sunspots, as well as the number of violent events depends on the state of the magnetic field

38. Variations in Sunspot Activity Maunder Minimum

39. Question 5: How many years elapse between times of maximum solar activity? • 3 • 5 • 11 • 33 • 105

40. Space Weather:What is it? Space Weather refers to conditions in space that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health. • Sun: • Energy released in the form of photons, particles, and magnetic fields • Sources of major disturbances: • Coronal Holes • Solar Flares • Coronal Mass Ejections • Solar Particle Events Earth

41. SPACE WEATHER

42. Space Weather Weather Hurricanes and Tornados Solar Corornal Mass Ejection

43. Space Weather

44. Geomagnetic Storm Effects Telegraph Operations - September 3, 1859 Boston (to Portland operator).--"Please cut off your battery entirely from the line for fifteen minutes." Portland.--"Will do so. It is now disconnected." Boston.--"Mine is also disconnected and we are working with the auroral current. How do you receive my writing?" Portland.--"Better than with our batteries on. Current comes and goes gradually." Boston.--"My current is very strong at times, and we can work better without batteries, as the aurora seems to neutralize and augment our batteries alternately, making the current too strong at times for our relay magnets. Suppose we work without batteries while we are affected by this trouble?" Portland.--"Very well. Shall I go ahead with business?" Boston.--"Yes. Go ahead." (Annual of Scientific Discovery, ed. by D.A. Wells, Boston, Gould and Lincoln, p414, 1860; Singer, H.J., Magnetospheric Pulsations, Model and Observations of Standing Alfven Wave Resonances, Thesis, UCLA, 1980.)

45. 1958 Geomagnetic Storm • On February 9, 1958 an explosive brightening was observed on the solar disk at the Sacramento Peak Observatory • A notice was radioed to the IGY Data Center on Solar Activity at the Univ. Colorado’s High Altitude Observatory in Boulder • 28 hours later one of the greatest magnetic storms on record began • It was the 13th most disturbed day from 1932 to the present • Effects: Toronto area plunged into temporary darkness Western Union experienced serious interruptions on its nine North Atlantic telegraph cables Overseas airlines communications problems Brooks, J., The Subtle Storm, New Yorker Magazine, 39-77, Feb. 7, 1959.

46. Weather NOAA National Weather Service Accuweather MONITORING SPACE WEATHER Space Weather NOAA Space Environment Center

47. Unveiling of U-Haul Truck Supergraphic Representing Colorado at Space Weather Week 2001 Graphic on the side of several thousand U-Haul Trucks www.uhaul.com/supergraphic

48. Solar “butterfly” diagram • At the beginning of the solar cycle, sunspots appear at high latitude on the Sun • As the cycle progresses, sunspots appear closer and closer to the solar equator

49. Dates to Remember • Reading, homework, quiz next week • HAND IN HOMEWORK • HAND IN ACTIVIES