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ASTR 1102-002 2008 Fall Semester

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  1. ASTR 1102-0022008 Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture03]

  2. University-wide, Gustav-motivated Calendar Modifications

  3. University-wide, Gustav-motivated Calendar Modifications

  4. Gustav’s Effect on this Course • Fall Holiday has been cancelled, which means our class will meet on Thursday, 9 October. (This makes up for one class day lost to Gustav last week.) • We will hold an additional makeup class on Saturday, 20 September! (This will account for the second class day lost to Gustav last week.) • Date of Exam #1 has been changed to Tuesday, 23 September!

  5. Course Syllabus

  6. Course Syllabus

  7. Chapter 17: The Nature of Stars

  8. Describe a Population of Stars

  9. Individual Stars… • Location in Space • Coordinate (angular) position on the sky [Right ascension & Declination] • Distance from Earth [use Stellar Parallax] • Motion through Space • Motion across the sky [“proper” motion] • Motion toward/away from us (radial velocity) [use Doppler Effect]

  10. Google Earth/Sky

  11. Stellar Parallax (§17-1) • Understand Figs. 17-1, 17-2, and eyes+thumb illustrations. • Star ‘A’ exhibits a stellar parallax that is twice as large as the stellar parallax exhibited by star ‘B’. • Which star is farther from us? • How much farther away? • If parallax angle (p) is measured in arcseconds and distance is measured in ‘parsecs’ (see §1-7 and Fig. 1-14), then ... • d = 1/p

  12. Stellar Parallax (§17-1) • Understand Figs. 17-1, 17-2, and eyes+thumb illustrations. • Star ‘A’ exhibits a stellar parallax that is twice as large as the stellar parallax exhibited by star ‘B’. • Which star is farther from us? • How much farther away? • If parallax angle (p) is measured in arcseconds and distance is measured in ‘parsecs’ (see §1-7 and Fig. 1-14), then ... • d = 1/p

  13. March sky image

  14. September sky image

  15. Stellar Parallax (§17-1) • Understand Figs. 17-1, 17-2, and eyes+thumb illustrations. • Star ‘A’ exhibits a stellar parallax that is twice as large as the stellar parallax exhibited by star ‘B’. • Which star is farther from us? • How much farther away? • If parallax angle (p) is measured in ‘arcseconds’ and distance is measured in ‘parsecs’ (see §1-7 and Fig. 1-14), then ... • d = 1/p

  16. Individual Stars… • Location in Space • Coordinate (angular) position on the sky [Right ascension & Declination] • Distance from Earth [use Stellar Parallax] • Motion through Space • Motion across the sky [“proper” motion] • Motion toward/away from us (radial velocity) [use Doppler Effect; §5-9]

  17. Motion Across the Sky(“proper” motion) http://www.psi.edu/~esquerdo/jim/astfov.gif

  18. Prominent and Obscured Objects

  19. Prominent and Obscured Objects

  20. NOTE: Transient Events (in time) also occur

  21. NOTE: Transient Events (in time) also occur

  22. NOTE: Transient Events (in time) also occur

  23. NOTE: Transient Events (in time) also occur

  24. NOTE: Transient Events (in time) also occur

  25. Individual Stars… • Location in Space • Coordinate (angular) position on the sky • Distance from Earth • Motion through Space • Motion across the sky (“proper” motion) • Motion toward/away from us (radial velocity) • Intrinsic properties • Brightness (luminosity/magnitude) • Color (surface temperature) • Mass • Age

  26. Stars of different brightness

  27. Stars of different colors

  28. Apparent brightness due to… • Each star’s intrinsic brightness • Each star’s distance from us

  29. Apparent Brightness varies with Distance

  30. Color-Temperature Relationship

  31. More About: Continuous Spectra from Hot Dense Gases (or Solids) • Kirchhoff’s 1st Law: Hot dense gas produces a continuous spectrum (a complete rainbow of colors) • A plot of light intensity versus wavelength always has the same general appearance (blackbody function): • Very little light at very short wavelengths • Very little light at very long wavelengths • Intensity of light peaks at some intermediate wavelength • But the color that marks the brightest intensity varies with gas temperature: • Hot objects are “bluer” • Cold objects are “redder”

  32. The Sun’s Continuous Spectrum (Textbook Figure 5-12)

  33. Wien’s Law for Blackbody Spectra • As the textbook points out (§5-4), there is a mathematical equation that shows precisely how the wavelength (color) of maximum intensity varies with gas temperature.