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04 The Sun Mc Neely
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04 The Sun Mc Neely

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  • 1. Astronomy Chapter 04 : The Sun Sunset over the Giza pyramids
  • 2. Sun & Earth
    • The sun is the star closest to earth
    • The sun provides light, heat, and energy for life
    • The sun is powered by nuclear fusion, the conversion of hydrogen into helium inside the sun
    • Ancient peoples such as the Egyptians, Greeks, and Aztecs worshipped the sun as a god
  • 3. Mythology of the Sun Clockwise from left: Egyptian, Greek, Aztec
  • 4. Luminosity
    • Luminosity is the sun’s total energy output
    • L = 3.85x10 26 watts (joules of energy per second)
    • Sun’s energy output is truly enormous and nearly inexhaustible
  • 5. Solar Constant
    • Solar Constant : Amount of solar energy that falls per second on earth’s outer atmosphere
    • Solar Constant = 1400 watts/m 2
    • One week of solar output equals the energy of all reserves of fossil fuels
  • 6. Astronomical Unit
    • Astronomical Unit (AU) is equal to the average earth-to-sun distance
    • 93 million miles (150 million km)
    • Used to measure distances in the solar system
  • 7. Solar System (AU) 39.5 Pluto 30 Neptune 19.2 Uranus 9.5 Saturn 5.2 Jupiter 1.5 Mars 1.0 Earth 0.7 Venus 0.4 Mercury Distance in AU Planet
  • 8. Size of Sun
    • Radius = 432,000 miles (696,000 km)
    • Sun = 99% of solar system mass
    • Angular Size = ½ degree, same as full moon
    • Sun is 400 times larger than the moon, yet 400 times more distant, so they appear about the same angular size
    • Remarkable coincidence allows solar eclipses
  • 9. Observing the Sun Safely
    • Solar projection through a telescope, the sun is observed safely on a screen
    • Never look at the sun through an unfiltered telescope!
  • 10. Solar Projection Solar projection during an eclipse Toward sun
  • 11. Origin of the Sun
    • Nebular Theory : Proposed by Immanuel Kant (1724-1804)
    • Sun and Planets formed together from a rotating cloud of gas and dust called the solar nebula about 5 billion years ago
    • Such nebulas are observed around young stars such as Beta Pictoris
  • 12. Nebular Theory Diagram The sun is believed to have been formed from a rotating disk of gas and dust, similar to the one observed around Beta Pictoris Beta Pictoris
  • 13. Elements in the Sun
    • Sun contains about 70 chemical elements
      • 73% Hydrogen
      • 25% Helium
      • 2% Other elements
  • 14. Sun’s Structure
    • Atmosphere
      • Corona
      • Chromosphere
      • Photosphere
    • Interior
      • Convection Zone
      • Radiation Zone
      • Core
  • 15. Sun Diagram
  • 16. Photosphere
    • The photosphere is the sun’s visible “surface”
    • Edge is termed the limb
    • Limb is darker than center, termed limb darkening (visible in telescope)
    • Photosphere can have a grainy appearance (granulation) in a good telescope
    • Sunspots visible
    • 10,000 K
    Granulation Photosphere “live”
  • 17. White Light Photosphere The safe solar filter covers the entire aperture of the telescope The solar photosphere can appear granular in a good telescope—note the limb darkening
  • 18. Limb Darkening
    • The photosphere appears slightly dimmer near its limb
    • This effect, limb darkening, is evident in this photograph of the sun
    http://users.otenet.gr/~a_evagel/Essay/faculae.htm
  • 19. Granulation
    • Grainy appearance of photosphere
    • Individual cells around 600 miles in diameter, represent rising and sinking columns of gas
  • 20. Sunspots
    • Sunspots are temporary, dark, cool patches on the sun’s bright photosphere
    • Sunspots can last from hours to months
    • Some visible to unaided eye at sunset or through hazy clouds
    • Chinese astronomers recorded sunspots as early as 800 BC.
  • 21. Sunspot Details
    • Range from the size of the earth to many earths
    • Umbra : Dark core
    • Penumbra : Grayish outer zone
    • Often appear in groups called active regions
    • Sunspots are created by variations in the sun’s magnetic field
    • First studied in west by Galileo (1610), he was able to deduce the sun’s rotational period
  • 22. Galileo’s Sunspot Observations A sketch of the sun by Galileo
    • Galileo was the first astronomer to observe the sky with a telescope
    • He used small, simple refracting telescopes that are crude by modern standards
  • 23. Identify umbra, penumbra, granules Sunspots http://www.spaceweather.com/swpod2006/14aug06/roel.jpg
  • 24. Chromosphere
    • The chromosphere is a thin, transparent layer about 6000 miles above photosphere
    • Visible during total eclipses, h-alpha telescope filters
    • Red layer, prominences visible
    Prominence, not the size of the earth for comparison Chromosphere “live”
  • 25. Chromosphere during Eclipse The chromosphere can be seen during eclipses as a red rim around the eclipsed sun
  • 26. Coronado PST Photo & Chromosphere A hydrogen-alpha filtered telescope, such as the Coronado PST, allows observation of the chromosphere at any time
  • 27. Prominences
    • Prominences resemble fiery outbursts along the edge of the sun
    • Represent gases held above solar surface by magnetic fields
    • Last for days to months
    • Named filaments when viewed on face of sun
  • 28. Prominences
  • 29. More Prominences http://www.spaceweather.com/swpod2006/09apr06/Chatman.jpg
  • 30. Filaments Dark filament, a prominence on the solar disk Note prominences around the solar limb in this H-Alpha photo
  • 31. Solar Features
  • 32. Corona
    • Corona is Latin, “crown”
    • Visible during total eclipses as a spiky, jagged white halo around the eclipsed sun, one of the most awesome sights in nature
    • Outermost atmosphere, extends millions of miles into space
    • High temp, up to 2 million K
    Corona “live”
  • 33. Totality, Awesome
  • 34. March 2006 http://www.buytelescopes.com/gallery/view_photo.asp?pid=8652&sg=1 Note the face of the moon is faintly visible in this highly processed image
  • 35. America’s Next Total Solar Eclipse-2017
    • Observers inside the red line will see a total eclipse
    • Observers within the shaded area will see a partial eclipse
  • 36. Interior
    • Below photosphere, temp and density increase with depth
    • Up 15 million degrees K inside, density 100 times that of water
    • Pressure = 200 billion earth atmospheres
    • Core, nuclear fusion powers the sun
    • Heat & energy of the sun provides pressure to balance the inward, crushing pull of gravity, keeps star intact as a sphere
  • 37. Equilibrium
    • Balance of two forces
    • Gravity-pushes inward
    • Gas pressure-pushes outward
    • Hydrostatic Equilibrium : Star’s radius represents a compromise between two forces
  • 38. Light from Within
    • Energy slowly transmitted out (radiative diffusion)
    • Takes about 20 million years for light from the core to reach the surface and become sunshine
  • 39. Sun’s Rotation
    • Sun rotates on an axis from west to east, just as the earth does
    • Sun is not a rigid body, different parts rotate at different speeds
    • Period of rotation = 25 days at equator, 35 days at poles
    • Termed differential rotation
  • 40. Solar Rotation
    • Note that sunspot groups on the sun appear to change position when observed for a few days in a row
    • The motion of sunspots reveals the sun’s rotation
  • 41. Rotation This animation shows the growth and rotation of sunspot 848, Jan. 19 th -21 st 2006 http://www.spaceweather.com/index.cgi
  • 42. Differential Rotation
    • Note the different rotation rates of the equator and poles of the sun
    • The interior rotates at a different rate also
    • The sun is a complex place!
  • 43. 11-Year Cycle
    • Number of sunspots rises and falls over an 11-year cycle
    • The highest part of the cycle is termed solar maximum, the lowest solar minimum
    • At solar max, the sun can display nearly 200 sunspots per year, at solar min it can approach zero
  • 44. Solar Cycles Present
  • 45. Cycle 23 (as of 2006) In what year did solar maximum occur? Minimum?
  • 46. Current Cycle http://www.swpc.noaa.gov/SolarCycle/
  • 47. Maunder Minimum
    • Period of low solar activity from 1645-1715, virtually no sunspots were visible for many years
    • Coincided with cold period in Europe (“Little Ice Age”)
    • River Thames froze solid
    • Apparently sunspots have a relationship to earth’s climate
  • 48. Butterfly Diagram
    • Sunspots tend to appear at high latitudes at the start of a solar 11-yr cycle
    • Latitudes shift toward solar equator through the rest of the cycle
    • Graph: Butterfly diagram
  • 49. Solar Magnetism
    • Sunspots act as huge magnets, have N and S poles
    • Entire sun exhibits a weak magnetic field offset 15 degrees from sun’s axis of rotation
    • Entire field extends out beyond Pluto
    • Magnetic polarity reverses every 11 years shortly after solar maximum, requires 22 years for a complete cycle
  • 50. Sunspot Magnetism Sunspots often appear in pairs displaying a north and south pole
  • 51. Flares
    • Solar Flare : A sudden, tremendous, explosive outburst of light, invisible radiation, and material from the sun
    • One great flare can equal the energy that would be used by the entire world in 100,000 years
    • Short, last a few minutes to a few hours
    • Occur near sunspot groups (active regions)
  • 52. Flare Effects
    • Can cause power outages, radio blackouts, electrical power outages, radiation hazard to astronauts
    • Cause of Northern Lights on earth (Aurora Borealis)
  • 53. Solar Flare This image was taken by the Soho satellite, a satellite devoted to observing the sun at various wavelengths
  • 54. Solar Flare Effects
  • 55. Aurora Borealis
    • Northern Lights, Southern Lights (Aurora Australis)
    • Bands of light visible from earth’s high latitudes, Arctic, and Antarctic; Occasionally lower (We can see them here sometimes)
    • Occur about 2 days after major solar flares
    • Occur when high-energy particles from the sun ionize gases in earth’s atmosphere
  • 56. Northern Lights
  • 57. Solar Wind
    • Solar Wind : A plasma, or stream of charged particles that flows outward from the sun at all times
    • Much faster, hotter, and thinner than earth wind
    • Solar wind escapes from the sun through “gaps” in the corona named coronal holes
    • Solar wind takes 4 days to reach earth, about 1 million miles/hour
    • Strongest during solar maximum
  • 58. Coronal Mass Ejections
    • CME : Coronal Mass Ejections, particularly large bursts of solar wind
    • Solar flares & CMEs emit blasts of solar wind, causing auroras and earth disturbances
  • 59. CME
    • In this image from a coronagraph, a cme appears to the right
    • The sun’s disk is represented by the small, central circle
    • Movie: http://sohowww.nascom.nasa.gov/bestofsoho/Movies/C3_Apr01/C3_Apr01sm.mpg
    http://solar-center.stanford.edu/magnetism/magnetismsun.html
  • 60. Earth’s Protective Shield
    • Earth’s magnetic field shields us from harmful bursts of solar radiation (solar wind and cmes)
    • Solar radiation is deflected around our planet
    Earth
  • 61. Heliopause
    • Heliopause : Edge of solar wind, lies beyond the orbit of Pluto
    • The heliopause represents the boundary marking the edge of the sun’s direct influence
    • Spacecraft from the 1970s and 80s, the Pioneers and Voyagers, will soon cross the heliopause
  • 62. Heliopause The heliopause marks the edge of the sun’s influence
  • 63. Motion in Space
    • Sun, like other stars, is racing through space
    • Apex of the Sun’s Way : Sun is speeding towards the star Vega at 45,000 mi/hr carrying the nine planets along with it
    • In consequence, the planets move in a spiral path through space as they orbit the moving sun
  • 64. Vega, the Apex of the Sun’s Way The direction of the sun’s motion through the galaxy is located near the star Vega on the celestial sphere
  • 65. Earth’s Spiral Motion Vega-Apex of the Sun’s Way Earth Sun
  • 66. Galactic Revolution
    • Sun & planets orbit the center of the Milky Way Galaxy at about 563,000 mi/hr
    • One revolution takes 230 million years
    • The sun is located about 28,000 ly from the Milky Way’s Center
  • 67. Sun’s Revolution in Milky Way

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