1. Survey of the Universe Tom Burbine tburbine@mtholyoke.edu

2. HW HW #4 and #5 are due this Wednesday

3. Stars have different colors

5. Surface Temperature Determine surface temperature by determining the wavelength where a star emits the maximum amount of radiation Surface temperature does not vary according to distance so easier to measure

7. 1913

8. Who were these people? These were the women (called computers) who recorded, classified, and catalogued stellar spectra Were paid 25 cents a day Willamina Fleming (1857-1911) classified stellar spectra according to the strength of their hydrogen lines Classified over 10,000 stars

9. http://www.youtube.com/watch?v=R6_dZhE-4bk

11. Fleming’s classification A - strongest hydrogen lines B - slighter weaker lines C, D, E, … L, M, N O - weakest hydrogen lines lines

12. Annie Jump Cannon (1863-1941) Cannon reordered the classification sequence by temperature and tossed out most of the classes She devised OBAFGKM http://andyrivkin.bandcamp.com/track/obafgkm

13. More information Each spectral type had 10 subclasses e.g., A0, A1, A2, … A9 in the order from the hottest to the coolest Cannon classified over 400,000 stars

15. OBAFGKM Oh Be A Fine Girl/Gal Kiss Me

17. http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap04/FG04_05.jpg

18. http://spiff.rit.edu/classes/phys301/lectures/spec_lines/spec_lines.html

19. http://scope.pari.edu/images/stellarspectrum.jpg

20. absorption line - A dark feature in the spectrum of a star, formed by cooler gas in the star's outer layers (the photosphere) that absorbs radiation emitted by hotter gas below.

21. Any Questions?