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Temperature, Color, Radius & Compositioni

Temperature, Color, Radius & Compositioni. Surface Temperature. Most light comes from photosphere – thin layer at bottom of atmosphere. Sun’s visible “surface” is photosphere. Hot & dense gas – emits continuous spectrum. Cooler, thinner gas – absorbs continuous light.

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Temperature, Color, Radius & Compositioni

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  1. Temperature, Color, Radius & Compositioni

  2. Surface Temperature

  3. Most light comes from photosphere – thin layer at bottom of atmosphere.. Sun’s visible “surface” is photosphere.

  4. Hot & dense gas – emits continuous spectrum Cooler, thinner gas – absorbs continuous light

  5. Sun’s spectrum Absorption lines The star Vega

  6. Originates at bottom of photosphere. Result of absorption.

  7. 12,000 K 6000 K Intensity 3000 K Wavelength 1. Location of peak of blackbody (continuous emission) curve yields temperature.

  8. Real Stars Intensity 50,000 K 10,000 K 6000 K (Sun) Wavelength

  9. Line Strength 10,000 K Temp. • Appearance (“Strength”) of the spectrum • lines reflects temperature. e.g., Hydrogen (“Balmer”) lines

  10. Appearance (“Strength”) of the spectrum • lines reflects temperature. Temp Wavelength

  11. Balmer Thermometer Balmer line transitions. •  High temp: most H is • ionized. • Low temp: most H is in ground state.

  12. Lines of many elements respond to temperature. Line Strength Temp.

  13. Color

  14. 12,000 K 6000 K Intensity 3000 K Wavelength * Star color is determined by temperature.

  15. Taurus (“The Bull”) T  13,000 K T  3500 K

  16. Radius

  17. D  d (AU)  (o) D = 865,000 mi Sun d 0.50 0.25 0.10 0.05 0.005 1 2 5 10 100

  18. In general . . . d &   D Sun: d = 1 AU,  = 0.5o D = 865,000 mi For other stars, it’s not so easy to get diameter . . .  Sun at 4 ly from Earth:  = 0.000002o

  19. Exception:Betelgeuse

  20. R 1 m2 E Another way to get radius . . . Stars radiate like blackbodies. From each sq meter, energy E radiated: E  T4 Total energyemitted by star = total surface area  E

  21. Chemical Composition

  22. Appearance of lines of element implies presence of element. • But, absence of lines does not imply absence of element. • e.g., Hydrogen •  Astronomers find: most stars dominated by • hydrogen & helium. • e.g., Sun: H 74% • He 25%

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