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PH0021 Astronomy Lecture 19 (The Sun) 021203v7 The Sun, in all its glory!

PH0021 Astronomy Lecture 19 (The Sun) 021203v7 The Sun, in all its glory!. Prof Rick Gaitskell Department of Physics Brown University See course pages for source http://gaitskell.brown.edu. Sun Data. The Sun - Photosphere. Size Scale Composition Compare terrestrial planets

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PH0021 Astronomy Lecture 19 (The Sun) 021203v7 The Sun, in all its glory!

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  1. PH0021AstronomyLecture 19 (The Sun)021203v7The Sun, in all its glory! Prof Rick Gaitskell Department of PhysicsBrown University See course pages for source http://gaitskell.brown.edu

  2. Sun Data

  3. The Sun - Photosphere • Size • Scale • Composition • Compare terrestrial planets • Compare Jovian planets • Sun • GAS/PLASMA - No solids, even at core, despite pressure… • Why does it appear as a well defined “ball”? • (i) Gas distribution is nearly spherical • (ii) Only seeing gas from thin layer of gas • PHOTOSPHERE • Thin layer of gas 400 km • 1/2000th radius (Rsun~0.7x106 km) • “Limb darkening”

  4. Absorption Lines - Photosphere

  5. The Sun - Structure of Photosphere Typical grain ~1000 km (hires solar images) [DEMO Silicon Oil & Al flakes]

  6. Chromosphere • Above Photosphere (rPhoto~0.01% of rEarth atmosphere) • Is even less dense Chromosphere (rChromo~0.01% of rPhoto ) • Difficult to see, except during real or artificial eclipse • Pink in colour! Why pink?? • Emission Spectrum [BOARD]

  7. Emission Lines

  8. Corona • Outermost layer of Sun is the Corona (“Crown”) • Requires eclipse (or coronagraph to observe) • Not sphereical • Streamers/projections • Emission lines [see next] indicate hotter than Chromosph. • Not just Fe+ but Fe13+ • => T~2x106 • Intensity? (Flux ~ sT4 )

  9. Corona in x-rays

  10. Coronal Mass Ejection • SOHO Satellite observation • C3 coronagraph • (obs range 3.5-30 solar corona radii) • Coronal Mass Ejection • 18 Feb, 2000 (Medium Sized) • Follows onset of solar flare previous day (but not necessarily linked) • Takes ~2 days to arrive (this one is heading direct for Eath, hence “halo” like appearance • Up to 109 tonnes plasma @ 0.01 c Like solar flares, they occur whenever there's a rapid, large-scale change in the sun's magnetic field. Solar flares and CMEs often occur together, but not necessarily because the flare triggers the CME or vice versa. One can happen without the other and frequently during solar maximum we see CMEs without an associated flare http://www.southpole.com/headlines/y2000/ast18feb_1.htm

  11. 5700K 4300K Photosphere6300K Sun Spots • And the Brightest and Hottest parts of Corona are… • …directly above another conspicuous feature: SUN SPOTS [DEMO]

  12. 26 days 36 days Differential Rotation of Sun • Sun Spot Observation • Clear that different horizontal bands (latitudes) rotate at different rates • Gallileo made first rot obs • (Live ~2 months) • Richard Carrington, 1859 • Differential rotation • Helioseismology • 1980’s able to determine how bulk is behaving

  13. Sun Spot Cycle (# of Sun Spots & Position) • 11 year cycle • i.e. ~11 years between max # • max -> min (no sun spots) -> max • Position migrates over cycle • Min -> Starts ~30 deg lat • Max as moves toward equator • Next Min as Spots annihilate at equator [BOARD]

  14. Zeeman Spliting of Abs. Lines in Sun Spots • George Hale 1908 • Permit determination of magnetic field strength and polarity

  15. Magnetic-Dynamo Model (explain 22-year cycle) • Horace Babcock 1960 • Proposes Magnetic-Dynamo Model to explain 22-year cycle (with polarity flips) • Makes use of • Differential Rotation • Convection See http://science.msfc.nasa.gov/ssl/pad/solar/quests.htm for dynamo discussion and figs

  16. Sun Spot Movie • First part • Differential Rotation of Sun Spots • Sphere is then mapped onto sheet • Second Part • Again see differential rotation • Makes higher latitudes move slower than equator • Evolution of Sun Spots over 22 year cycle • 1980 max • Top Hemisph: Yellow leads Blue • Bot Hemisph: Blue leads Yellow • 1986 minima • 1991 max (Poles Reversed) • Top Hemisph: Blue leads Yellow • Bot Hemisph: Yellow leads Blue • 1997 minima http://science.msfc.nasa.gov/ssl/pad/solar/images/MagMovie.mov

  17. Solar Flares

  18. Hydrostatic Equilibrium • [DEMO - Balloons]

  19. Regions of Sun • What happens at radius~0.7? • Inside - radiation • Outside - convection • T is low enough that neutral hydrogen forms • H absorbs visible light much better • Opacity increases • ->Convection

  20. Summary • Starting at the top… • Corona (Flares/CME) • Very high temperature gas/plasma • Flares (hot ionized gas from sun spot) and CME (larger amounts of coronal gas) • Chromasphere • Photosphere (Sun Spots) • 400 km thick, 5800 K (Blackbody appears Yellow) • Sun spots show 22-year cycle (magnetic behaviour of Sun) • Convection Zone [cell structure] • Radiation Zone [r<0.7] • Core (Fusion) [r<0.25] • Has it gone out, no! We see neutrinos! • But not as many as we expected…particle physics!

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