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ASTR 1102-002 2008 Fall Semester

This lecture discusses the nature of stars, including their location in space, angular position on the sky, distance from Earth (using stellar parallax), motion through space, motion across the sky (proper motion), and motion toward/away from us (radial velocity). It also covers the relationship between brightness, color, mass, and age of stars, as well as the color-temperature relationship and the Sun's continuous spectrum.

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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.

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