Life Cycles Of Stars


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Life Cycles Of Stars

  1. 1. The Stars
  2. 2. The Sun is a Star
  3. 3. Surface of the Sun
  4. 4. Solar Prominence
  5. 5. Solar Corona
  6. 6. The Stars in the Sky <ul><li>Vary in Brightness </li></ul><ul><li>Distance </li></ul><ul><li>Size </li></ul><ul><li>Vary in Color </li></ul><ul><li>Color = Temperature </li></ul>
  7. 7. Star Names <ul><li>Proper star names mostly Arabic </li></ul><ul><li>Greek Letters, Numbers </li></ul><ul><li>Catalog Identifiers </li></ul><ul><li>Faint stars usually have no name </li></ul>
  8. 8. Constellations <ul><li>89 in number </li></ul><ul><li>Based on Near Eastern myths via the Greeks </li></ul><ul><li>Some 17 th -18 th century Invented Constellations </li></ul><ul><li>Now Have Formal Boundaries </li></ul><ul><li>Every star is in one and only one constellation </li></ul><ul><li>Constellations are entirely human inventions. They are not “Really” in the sky. </li></ul>
  9. 9. The Southern Cross
  10. 10. A Myth in the Autumn Sky
  11. 11. A Star Map
  12. 12. Western Constellations
  13. 13. Chinese Constellations
  14. 14. The Heavens Are Not Changeless <ul><li>The Stars Move </li></ul><ul><ul><li>Most of our constellations would have been unrecognizable to Neanderthal Man </li></ul></ul><ul><li>The Solar System Moves </li></ul><ul><ul><li>Very few of our nearby stars would have been visible to the first humans </li></ul></ul><ul><li>Stars are Born, Live and Die </li></ul><ul><ul><li>Many of our brightest stars did not exist in the days of the dinosaurs </li></ul></ul>
  15. 15. Parallax and the Distances of Stars <ul><li>Stars appear identical all over Earth </li></ul><ul><li>They do show slight parallax shift from opposite sides of Earth’s orbit </li></ul>
  16. 16. Parallax: pre-1997 <ul><li>Parallax is tiny - was once used as argument against motion of the Earth </li></ul><ul><li>One second of arc = size of a quarter at 5 km (3 mi.) </li></ul><ul><li>Parallax angle of nearest star (4.3 l.y.) is 0.75” </li></ul><ul><li>Accuracy limited by Earth’s atmosphere </li></ul><ul><li>Fairly accurate to 30-40 l.y., rough to 100 </li></ul>
  17. 17. Hipparcos <ul><li>Named for ancient Greek astronomer who catalogued the stars </li></ul><ul><li>Hi gh P recision Par allax Co llecting S ystem </li></ul><ul><li>Launched by European Space Agency, 1989 </li></ul><ul><li>Data Collection 1989-1993 </li></ul><ul><li>Data Analysis 1993-1997 </li></ul>
  18. 18. The Hipparcos Data <ul><li>118,218 stars measured: parallax and motion </li></ul><ul><li>22,396 accurate to 10% - a 20-fold improvement </li></ul><ul><li>Stars out to 200-300 l.y. are known to within 10% </li></ul><ul><li>30,000 more accurate to 20% </li></ul><ul><li>All pre-Hipparcos distance data is obsolete </li></ul>
  19. 19. Brightness of Stars <ul><li>Variations in distance and intrinsic brightness </li></ul><ul><li>Scale based on one by Hipparcos 500 B.C. </li></ul><ul><li>Magnitude: Large Numbers = Fainter </li></ul><ul><ul><li>One magnitude = 2.5 x </li></ul></ul><ul><ul><li>Five magnitudes = 100 x </li></ul></ul>
  20. 20. Magnitudes <ul><li>Planet around nearby star: 30 </li></ul><ul><li>Pluto: 13 </li></ul><ul><li>Faintest Naked-Eye Star: 6 </li></ul><ul><li>Big Dipper Stars: 2 </li></ul><ul><li>Sirius (Brightest Star) -1.6 </li></ul><ul><li>Venus -4 </li></ul><ul><li>Full Moon -12 </li></ul><ul><li>Sun -27 </li></ul>
  21. 21. Absolute Magnitude <ul><li>Altair and Deneb are about equally bright as seen from Earth </li></ul><ul><li>Altair is 16 l.y. away, Deneb 1600 </li></ul><ul><li>Hence Deneb must be about 10,000 times brighter </li></ul>
  22. 22. Absolute Magnitude <ul><li>How bright a star would be at a distance of 32.6 l.y. (10 parsecs) </li></ul><ul><li>Sun: 4.5 (inconspicuous naked-eye star) </li></ul><ul><li>Altair: 2.2 </li></ul><ul><li>Deneb: -7.1 (bright as crescent moon) </li></ul><ul><ul><li>Note: Deneb - Altair about 10 magnitudes = 100 x 100 = 10,000 times </li></ul></ul>
  23. 23. Black-Body Radiation <ul><li>Objects Emit Radiation Because They Are Hot </li></ul><ul><li>Why “Black”? Because None of the Radiation is Reflected from Some Other Source </li></ul><ul><li>The Sun Emits Black-Body Radiation, the Moon Does Not </li></ul>
  24. 25. Color = Temperature
  25. 26. Why Black-Body Radiation is so Important <ul><li>Color is directly related to temperature </li></ul><ul><li>Temperature is the only determinant of color </li></ul><ul><li>Energy per unit area is the same if temperature is the same </li></ul><ul><ul><li>If two stars have the same color and distance, difference in brightness is due to difference in size </li></ul></ul><ul><ul><li>Dwarf and giant stars are literally dwarfs or giants </li></ul></ul>
  26. 27. Spectroscopy <ul><li>Different atoms absorb or emit specific wavelengths of light </li></ul><ul><li>When light spread into a spectrum, the absorbed wavelengths show up as dark (missing) bands </li></ul><ul><li>These spectral lines are indicators of: </li></ul><ul><ul><li>Chemical composition </li></ul></ul><ul><ul><li>Physical conditions </li></ul></ul>
  27. 28. Atoms and Radiation
  28. 29. The Solar Spectrum
  29. 30. Spectral Lines are Affected By: <ul><li>Electrical and Magnetic Fields </li></ul><ul><li>Number of Electrons Atoms Have Lost (Indicates Temperature and Pressure) </li></ul><ul><li>Motion (Doppler Effect) </li></ul><ul><li>Blue-shifted if Motion Toward Observer </li></ul><ul><li>Red-shifted if Motion Away From Observer </li></ul>
  30. 31. The Doppler Effect
  31. 32. The Doppler Effect
  32. 33. What the Doppler Effect Tells Us <ul><li>Radial Motion </li></ul><ul><li>Rotation of Stars </li></ul><ul><ul><li>Approaching side of star blue-shifted, receding side red-shifted </li></ul></ul><ul><li>Unseen Companions (Stars or Planets) </li></ul><ul><ul><li>Star oscillates around center of mass </li></ul></ul><ul><li>Surface and Interior Motions </li></ul><ul><ul><li>Changes in Size </li></ul></ul><ul><ul><li>Interior Oscillations </li></ul></ul>
  33. 34. The Hertzsprung-Russell Diagram
  34. 35. How Stars Form <ul><li>Collapsing gas and dust cloud </li></ul><ul><li>Protostar - mostly infrared </li></ul>
  35. 36. Main Sequence Stars <ul><li>Brown Dwarf </li></ul><ul><li>Red Dwarf </li></ul><ul><li>Normal Star </li></ul>
  36. 37. All Objects Exist Because of a Balance Between Gravity and Some Other Force <ul><li>People, Planets-Interatomic Forces </li></ul><ul><li>Normal Stars-Radiation </li></ul><ul><li>White Dwarfs-Electron Repulsion </li></ul><ul><li>Neutron Stars-Nuclear Forces </li></ul><ul><li>Black Holes-No Known Force </li></ul>
  37. 38. How Stars Die <ul><li>Main Sequence Stars Brighten With Age </li></ul><ul><li>The More Massive a Star, the Faster it Uses Fuel </li></ul><ul><li>Giant Phase </li></ul><ul><li>White Dwarf </li></ul><ul><li>Supernova </li></ul><ul><ul><li>Neutron Star - Pulsar </li></ul></ul><ul><ul><li>Black Hole </li></ul></ul>
  38. 39. Historical Supernovae <ul><li>1006 - Chinese </li></ul><ul><li>1054 - Chinese, European, Anasazi? </li></ul><ul><li>1572 - Tycho’s Star </li></ul><ul><li>1604 - Kepler’s Star </li></ul><ul><li>1987 - Small Magellanic Cloud (170,000 l.y.) </li></ul>
  39. 40. Life (Briefly!) Near a Supernova <ul><li>Sun’s Energy Output = 77 billion megatons/second </li></ul><ul><li>Let’s relate that to human scales. What would that be at one kilometer distance? </li></ul><ul><li>77 x 10 15 tons/(150 x 10 6 km) 2 = 3 tons </li></ul><ul><li>Picture a truckload of explosives a km away giving off a one-second burst of heat and light to rival the Sun </li></ul>
  40. 41. Now Assume the Sun Goes Supernova <ul><li>Brightens by 100 billion times </li></ul><ul><li>Our 3 tons of explosive becomes 300,000 megatons </li></ul><ul><li>Equivalent to entire Earth’s nuclear arsenal going off one km away - every second </li></ul><ul><li>This energy output would last for days </li></ul>
  41. 42. Planetary Systems <ul><li>Protoplanetary Disks </li></ul><ul><li>Accretion of Planets </li></ul><ul><li>Expulsion and Migration of Planets </li></ul><ul><li>About 120 extrasolar planets known </li></ul><ul><li>Our Solar System may be unusual? </li></ul>
  42. 43. Protoplanetary Disks in Orion