The Outer Layers of the Sun

1. The Outer Layers of the Sun • The Photosphere • The Chromosphere • The Corona • The Heliosphere

2. The Chromosphere 2,500 km think irregular region above photosphere of hot thin gas. Density is about a million times less than the top of the photosphere and the temperature rises to 10,000 K.

4. Discussion If the chromosphere is so much hotter than the photosphere, why does it not shine brighter than the photosphere? Why do you think it is red?

6. Calcium K line at 393.4 nm

7. What makes the chromosphere so hot? The chromosphere is heated from above by the solar corona.

11. Plages Bright patches surrounding sunspots. Plages are associated with concentrations of magnetic fields.

14. Filaments & prominences are the same thing!

15. Prominences Two types: • Quiescent – can last for months • Active – last only for hours. Lie above sunspots and have violent motions.

16. Hedgerow Prominence

20. Flares Sudden violent explosions in magnetically active regions. Last from 1 to 20 minutes and release as much energy as 2.5 million 100-megaton nuclear bombs in an area about the size of Earth. This is enough energy to cause thermonuclear fusion to take place on the Sun’s surface.

22. The Transitional Region A thin region (can be as thin as a few 10’s of km) above the chromosphere where the temperature rises from 10,000 K to 1 million K typical of the corona.

25. Corona Outer part of the Sun’s atmosphere. About as bright as the quarter phase Moon, it is visible only when the light of the photosphere is blocked. The corona is so thin that on Earth we would consider it a vacuum.

27. The Corona is surprisingly hot The temperature of the corona is over 1 million K.

28. Discussion At the distance of the Earth’s orbit the corona, although cooler than near the Sun, is still 0.14 million K. Why don’t astronauts burn up when they go on space walks?

29. Discussion What causes the helmet shaped structures in the corona? Why isn’t the corona spread out uniformly around the Sun?

30. Coronal Mass Ejection Giant magnetic bubbles that can hurl 5 to 50 billion tons of matter at speeds of 400 km/sec. 70% of coronal mass ejections are associated with, or followed by, erupting prominences. While 40% are accompanied by solar flares that occur at about the same time and place.

34. The Sun-Earth connection Coronal mass ejections and solar flares can be directed at Earth. Luckily for us, Earth has a magnetic field and an atmosphere to protect us.

37. Aurora When high speed particles from the Sun collide with atoms in Earth’s upper atmosphere. The electrons are knocked into higher energy orbitals and emit light when returning to the ground state.

39. Solar Wind Although the Sun’s surface gravity is much higher than the Earth’s, it is not able to contain particles with a temperature on over a million K. Thus the hot corona spews matter constantly (not just during flares, CME, and explosive prominences) into space at a rate of about 1 million tons per second.

41. Exam Next Wednesday essay & multiple choice questions Covers chapters 1-8, S1 & 14 Allowed one standard sheet of notes with writing on one side only

42. Terrestrial planet geology

43. Terrestrial Planets All the terrestrial planets are more or less differentiated, i.e. the densest materials have sunk to the core and the lighter materials have floated to the surface. The terrestrial planets were all completely molten at some time in the past.

45. Discussion Why do you think all the terrestrial planets were so hot in the past? Isn’t space rather cold?

46. Terrestrial planets interior structure Core – highest density material, mostly iron and nickel Mantle – high density silicate rocks Crust – lower density silicate rocks, granite and basalt.

48. Discussion What’s a silicate? Give and example of a silicate.

50. Earth’s internal structure • Solid crust – 5 km thick under the oceans, made of basalt: silicates of aluminum, magnesium and iron with a density of about 3.5 g/cm3. Under the continents the crust is 35 to 70 km thick and is made mostly of granite: silicates of aluminum, sodium and potassium with a density of 3.0 g/cm3. The continents float on the basalt.