1. Starlight continued
How study of stellar spectra reveals the nature of the stars

2. Spectra (plural of spectrum)
The solar spectrum
A fundamental measurement to extract more information from starlight
Spread out light according to wavelength
See Section 16.5

3. Kirchoff’s Laws of Radiation
Demo of Kirchoff’s 3rd Law

4. Kirchoff’s First Law + Wien’s Law
Hot, opaque objects produce continuous spectrum
The hotter the object, the bluer it is
Wien’s Law wmax = 2.9E-03/T
The hotter an object, the brighter it is
demo

5. Why does Wien’s Law look like that?
A physicist is bothered when he or she sees an equation like:
The form which emerges from fundamental equations of physics is:

6. What is the little “h” that appears in the correct form of Wien’s Law?
The speed of light
The scale height of the Sun’s atmosphere
The Universal Gas constant
Planck’s constant
The electrical charge of the electron

7. Kirchoff’s First Law + Wien’s Law

8. Important point: a hotter blackbody is brighter at all wavelengths than a cooler blackbody of the same size

9. Kirchoff’s Third Law: Absorption Spectra
See Figure 16.6

10. Starlight…application of spectroscopy to stars
Continuous spectrum gives surface temperature (Wien’s Law)
Spectral lines give chemical composition, temperature (also), speed of rotation (How?) and other properties
Examples of stellar spectra…what can we say?

11. Spectral classes of stars: O,B,A,F,G,K,M
What can you say about the temperatures of these stars?

12. Examples of stellar spectra
Question: apply Wien’s
Law to the O5 star. What
Can you say about its
Temperature (relative to the
Sun?)

13. With information provided by spectroscopy, we can search for correlations between stellar properties

14. What the data show: the Hertzsprung-Russell Diagram
Highest quality data from the Hipparchus spacecraft

15. The Sun is generically related to most other stars. How? Why?
The Sun is here
The Sun is generically related to most other stars. How? Why?

16. Filling out the Hertzsprung-Russell diagram

17. The Hertzsprung-Russell Diagram and the Types of Stars
See Figure 16.20
Types of stars, important terms
Main Sequence (luminosity class V)
Giants (luminosity class III)
Supergiants (luminosity class I)
White dwarfs
What does it all mean?

18. The Hertzsprung-Russell Diagram

19. The scientific classification scheme for the Sun
The Sun is a class G2V star…the Galaxy probably has a billion of them

20. The Hertzsprung-Russell diagram is a plotting board for the nature and evolution of stars