Our Sun Our Star. Image credit: JAXA. OU-L P SC 100 Spring, /81

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1 Our Sun Our Star Image credit: JAXA OU-L P SC 100 Spring, /81 1

2 Diameter: 1,400,000 km = 864,000 miles = 4.5 light-seconds 1,300,000 Earths could fit inside! 109 Earths would fit across the diameter of the sun OU-L P SC 100 Spring, /81 2

3 Mass: 2 x kg or 330,000 times Earth s mass Density: 1.41 g/cm 3 OU-L P SC 100 Spring, /81 3

4 What planet has this same composition? 4 OU-L P SC 100 Spring, /81

5 Surface temp: 5800 K, 5500 o C, 11,000 o F Luminosity total energy output at all wavelengths = 4 x watts/second (more than 6 moles of 100 watt light bulbs) OU-L P SC 100 Spring, /81 5

6 4.5 million metric tons of H are converted to He every second Expected lifetime: 10 billion years Distance from earth: 1 A.U. = 93,000,000 miles = 150,000,000 km = 8.33 light minutes OU-L P SC 100 Spring, /81 6

7 1 rotation takes 27.5 days at the equator, but 31 days at the poles! (Differential rotation) How was this determined? OU-L P SC 100 Spring, /81 7

8 Image Credit: SOHO 8 OU-L P SC 100 Spring, /81

9 OU-L P SC 100 Spring, /81 9

10 The Sun s Structure 3 Interior Layers The core produces the energy The radiative zone The convective zone 3 Atmosphere Layers Photosphere Chromosphere Corona OU-L P SC 100 Spring, /81 10

11 OU-L P SC 100 Spring, /81 11

12 OU-L P SC 100 Spring, /81 12

13 The Core 16,000,000 K (a star s core must be at least 8,000,000 K to start fusing H to He. no real atoms, only a soup of protons, electrons, and some larger atomic nuclei (He and C). all radiation produced is gamma (γ) OU-L P SC 100 Spring, /81 13

14 Radiative Layer not hot enough for fusion normally transparent gases have become opaque to light. Photons of light bounce from one atom to another in a random walk, like a gigantic pinball game. OU-L P SC 100 Spring, /81 14

15 Radiative Layer A given photon may take 100,000 years to reach the next layer. As photons travel, they slowly lose energy, shifting down towards the X- ray region of the spectrum. Temperature of this layer falls with increasing distance from core. OU-L P SC 100 Spring, /81 15

16 Convective Zone Still hot enough to be opaque to light. Currents of gas move vertically, like water boiling in a pan. Energy is transported by convection, not by radiation. This layer is like earth s mantle. OU-L P SC 100 Spring, /81 16

17 OU-L P SC 100 Spring, /81 17

18 The tops of convection cells can be seen near the sunspots. They are called granules, or granularity. Image Credits: SOHO/NASA/ESA and JAXA OU-L P SC 100 Spring, /81

19 Granularity movie 19 OU-L P SC 100 Spring, /81

20 The Photosphere Innermost of the sun s atmosphere layers. Gas cools enough that it becomes transparent to light. Sunlight originates from this layer. This is the surface that we see. Only 300 km thick. OU-L P SC 100 Spring, /81 20

21 Actual color of photosphere OU-L P SC 100 Spring, /81 is slightly greenish. 21

22 The Chromosphere 2 nd atmosphere layer. Glows in red H-α light (the red line from the level 3 level 2 electron transition in H atoms). Filters out the greenish color of the photosphere, so we see yellow light. Several thousand kilometers thick. OU-L P SC 100 Spring, /81 22

23 OU-L P SC 100 Spring, /81 Image Credit: SOHO/NASA/ESA 23

24 The Corona Millions of kilometers thick, but extremely low density. Sun s magnetic field agitates corona, raises temperature back up to about 2,000,000 K. Only visible during a total solar eclipse, or from space with specially designed telescopes. OU-L P SC 100 Spring, /81 24

25 OU-L P SC 100 Spring, /81 25

26 Features on the Sun s Surface Produced by sun s magnetic field. Prominences & flares. Sunspots Coronal Holes Coronal Mass Ejections OU-L P SC 100 Spring, /81 26

27 Differential Rotation Differential rotation winds up and tangles the magnetic field, resulting in surface storms. Process is not very well understood. OU-L P SC 100 Spring, /81 27

28 OU-L P SC 100 Spring, /81 28

29 OU-L P SC 100 Spring, /81 29

30 There s still a lot we don t know Why doesn t the sun have activity all the time? The magnetic field should be winding up and tangling constantly. Does the sun produce the same strength of magnetic field all the time? Is it structured differently at some times than at others? OU-L P SC 100 Spring, /81 30

31 31

32 Prominences & Flares When a loop of the sun s magnetic field projects out from the surface, some of the hot gas from the photosphere may flow along the field lines in arcs or loops, called prominences. OU-L P SC 100 Spring, /81 32

33 A loop prominence lets us visualize the magnetic field. OU-L P SC 100 Spring, /81 33 Image Credit: TRACE/NASA

34 34

35 OU-L P SC 100 Spring, /81 35 Image Credit: SOHO/NASA/ESA

36 Flares Sometimes, the magnetic field lines disconnect from the sun. Hot gas trapped inside the new loop of magnetic field travels outward from the sun as a solar flare. OU-L P SC 100 Spring, /81 36

37 OU-L P SC 100 Spring, /81 Image Credit: SOHO/NASA/ESA 37

38 Sun spots Where the loops of magnetic field penetrate the sun s surface, they cool it. Sunspots occur in pairs of (+) and (-) polarity. Sunspots are still about 3500 K hot enough to melt anything on the earth, but 2000 K cooler than the surrounding surface. OU-L P SC 100 Spring, /81 38

39 OU-L P SC 100 Spring, /81 39

40 OU-L P SC 100 Spring, /81 40

41 Umbra Penumbra OU-L P SC 100 Spring, /81 41

42 Sunspot Cycle The number of sunspots varies from year to year, along with the overall magnetic activity of the sun. We re used to hearing of an 11 year cycle. That s only for the overall number of sunspots. OU-L P SC 100 Spring, /81 42

43 Sunspot Cycle The real cycle is years long, and includes 11 years of the magnetic field with (+) polarity, then another 11 years with (-) polarity. We also see sunspots migrate from high latitudes to nearer the equator as the cycle progresses. OU-L P SC 100 Spring, /81 43

44 OU-L P SC 100 Spring, /81 44

45 You are here OU-L P SC 100 Spring, /81 45

46 Sometimes, the cycle quits! 1645 to 1715, few sunspots observed. Maunder Minimum. Mini ice age across Europe. OU-L P SC 100 Spring, /81 46

47 OU-L P SC 100 Spring, /81 47

48 Coronal Holes Actual holes or windows in the sun s corona Solar wind can easily blow through. When one of these points towards the earth, the velocity and density of the solar wind increases. OU-L P SC 100 Spring, /81 48

49 A coronal hole a window to the interior. OU-L P SC 100 Spring, /81 49 Image Credit: SOHO/NASA/ESA

50 You can see the solar wind blowing thru several coronal holes. OU-L P SC 100 Spring, /81 50 Image Credit: SOHO/NASA/ESA

51 One of the worst events During the active phase, the magnetic field sometimes gets tangled up so tight, that the sun blows off a portion of its entire corona. This is a coronal mass ejection (CME). A CME can be very damaging to electrical systems on the earth. OU-L P SC 100 Spring, /81 51

52 CME in progress OU-L P SC 100 Spring, /81 52 Image Credit: SOHO/NASA/ESA

53 Watch a CME in progress OU-L P SC 100 Spring, /81 53

54 CME s are made up of charged particles, have magnetic and electrical fields. Fields cause electrical systems to build up abnormally high voltages. In the winter of , a CME knocked out power to all of eastern Canada & the northeastern US for nearly a week. OU-L P SC 100 Spring, /81 54

55 Satellites are damaged by CME s, so we spend $ on special shielding. Communications, especially broadcast radio & TV, can be knocked out by CME s for hours at a time. OU-L P SC 100 Spring, /81 55

56 Missions to the Sun SOHO Ulysses Genesis TRACE Hinode ( Sunrise - Japan s version of SOHO) OU-L P SC 100 Spring, /81 56

57 SOHO (Solar and Heliospheric Observatory) a joint venture between ESA & NASA. Looks continuously at the sun from a fixed spot in space. Observes flares, CME s & comets falling into the sun! OU-L P SC 100 Spring, /81 57

58 OU-L P SC 100 Spring, /81 sohowww.nascom.nasa.gov/ 58

59 Ulysses designed to orbit over the sun s poles & provide a perspective that we can t get from earth. This is ESA s logo. 59 OU-L P SC 100 Spring, /81

60 Ulysses mission 60 ulysses.jpl.nasa.gov/ OU-L P SC 100 Spring, /81

61 Genesis Mission The Genesis mission was designed to orbit the sun and collect samples of the solar wind. It returned these particles to Earth for examination. Genesis orbited at a point called the L1 Lagrange point - a place in space where earth s gravity exactly cancels the sun s gravity. OU-L P SC 100 Spring, /81 61

62 OU-L P SC 100 Spring, /81 genesis.lanl.gov/ 62

63 Genesis Solar Wind Sampling Mission genesismission.jpl.nasa.gov/ 63

64 The TRACE spacecraft (Transition Region and Coronal Explorer) provides images like these. 64

65 NASA s twin Stereo spacecraft, launched in 2006, observe the sun from different points in space, allowing us to see ALL of the sun for the first time! 83 65

66 84 The Solar Dynamics Observatory or SDO now complements SOHO with more modern instruments. It is the most recent addition to the solar fleet, launched in Feb

67 How does the sun make its energy? Fusion of H to He occurs in a process called the proton-proton chain. Larger, heavier stars fuse H to He using C, N, and O (CNO cycle) OU-L P SC 100 Spring, /81 67

68 A review of the symbols a proton: 1 1H or p + (a proton is the nucleus of a normal hydrogen atom.) neutron: n o electron: e - positron: e + (a positively charged electron or antimatter ) OU-L P SC 100 Spring, /81 68

69 more particles actors on the stage neutrino: ν (a tiny, nearly massless particle with no charge that barely interacts with normal matter.) gamma ray: γ (the highest energy form of light) OU-L P SC 100 Spring, /81 69

70 Isotopes / nuclear symbols What does 4 2He mean? How many p +, n o in 56 26Fe? neutrons are the nuclear glue that hold a nucleus together. OU-L P SC 100 Spring, /81 70

71 The first collision of three The first step in the p-p chain is the collision of 2 protons. One proton immediately shatters, becoming a neutron. The new neutron gets rid of its (+) charge by giving off a positron (e + ) and a neutrino (ν). The resulting p + n o is a deuterium nucleus. 71 OU-L P SC 100 Spring, /81

72 p + ν e + e - γ p + n o p + OU-L P SC 100 Spring, /81 72

73 A 2 nd collision Another high speed proton (p + ) collides with the deuterium nucleus (p + n o ) and sticks. This collision gives off a gamma ray (γ) The result is a 3 2He nucleus: (p 2 n o ) +2. OU-L P SC 100 Spring, /81 73

74 p + n o γ (p 2 n o ) +2 p + OU-L P SC 100 Spring, /81 74

75 Collision #3 Two 3 2He nuclei (p 2 n o ) +2 collide headon to form a normal helium nucleus, 4 2 He. In the process, they give off 2 protons. OU-L P SC 100 Spring, /81 75

76 (p 2 n o ) +2 p + (p 2 n o 2) +2 (a He nucleus) (p 2 n o ) +2 The 2 protons OU-L P SC 100 Spring, /81 p + start the chain over. 76

77 Image Credit: atropos.as.arizona.edu/ OU-L P SC 100 Spring, /81 Here s the overall p-p chain 77

78 What goes in: 6 protons (H nuclei) What comes out: 1 He nucleus 2 protons 2 positrons 2 neutrinos 2 gamma rays (4 gamma rays if you count the annihilation of the positrons) OU-L P SC 100 Spring, /81 78

79 The Neutrino Problem Until recently, we could only detect about 1/3 of the neutrinos we ought to observe from the p-p chain. For the past several years, solar scientists weren t sure if their model was correct. OU-L P SC 100 Spring, /81 79

80 The Neutrino Problem Neutrinos are detected by the flashes of light (scintillations) they produce as they interact with water molecules in huge tanks underground (to minimize interference from cosmic rays.) OU-L P SC 100 Spring, /81 80

81 Super Kamiokande neutrino detector, Japan. Image Credit: pbs.org 81 OU-L P SC 100 Spring, /81

82 Neutrino Problem Solved! Neutrinos change type (or flavor ) while they re on their way from the sun. Counting these other flavors of neutrinos gives a total that s just what s expected. This also proves that neutrinos have mass (tiny, but measurable.) OU-L P SC 100 Spring, /81 82

83 Sun in 3 different ultraviolet wavelengths. OU-L P SC 100 Spring, /81 Image Credit: SOHO/NASA/ESA 83

84 Additional Credits solar-heliospheric.engin.umich.edu/ solar.physics.montana.edu/ helio.estec.esa.nl/ulysses/ csep10.phys.utk.edu/ Peters Planetarium Image Library, for images not otherwise credited. 84

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