1. H Atom 21 cm Line

3. Is the Milky Way a Spiral Galaxy like this one?

4. Because of the scattering by gas and dust in the disk

5. S   1-4

6. Because of the scattering by gas and dust in the disk S   1-4 We can only see (in the visible) about 1/6 (ca 6000ly) of the way to the Galactic Centre

7. View towards the Galactic Centre

9. Nuclear and electron spins paired

11. Nuclear and electron spins parallel

12. F = I+S = 0 F = I+S = 1 Nuclear and electron spins paired Nuclear and electron spins parallel

13. F = I+S = 0 F = I+S = 1 Fermi and Hargreaves Contact Term Nuclear and electron spins paired Nuclear and electron spins parallel

14. Classical picture of the nucleus as a spinning charge shell which gives rise to two magnetic field regions B = B int + B ext

15. Classical picture of the nucleus as a spinning charge shell which gives rise to two magnetic field regions B = B int + B ext

16. Classical picture of the nucleus as a spinning charge shell which gives rise to two magnetic field regions B = B int + B ext B int internal uniform magnetic field

17. Classical picture of the nucleus as a spinning charge shell which gives rise to two magnetic field regions B = B int + B ext B int internal uniform magnetic field B ext external magnetic field dipolar

18. s electron Electron density r

19. s electron p electron Electron density r

20. s electron p electron Electron density r H = B nucleus.  electron

21. r H =  B nucleus (r).  e (r) d 

22. s electron density r H =  B nucleus (r).  e (r) d 

23. s electron density r External dipolar term H =  B nucleus (r).  e (r) d 

24. s electron density r dipolar term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext )

25. s electron density r dipolar term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d  + B ext (r).  e (r)d 

26. s electron density r dipolar term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d  + B ext (r).  e (r)d 

27. s electron density r dipolar term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

28. s electron density r dipolar term B nucleus  I H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

29. s electron density r dipolar term B nucleus  I  e  S H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

30. s electron density r dipolar term B nucleus  I  e  S H = a I. S H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

31. s electron density r dipolar term B nucleus  I  e  S H = a I. S Fermi contact term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

32. a = (8  /3h) g e  B g H  N  (0)  2

33. g e electron g factor

34. a = (8  /3h) g e  B g H  N  (0)  2 g e electron g factor  B Bohr magneton

35. a = (8  /3h) g e  B g H  N  (0)  2 g e electron g factor  B Bohr magneton g H proton g factor

36. a = (8  /3h) g e  B g H  N  (0)  2 g e electron g factor  B Bohr magneton g H proton g factor  N nuclear magneton

37. a = (8  /3h) g e  B g H  N  (0)  2 g e electron g factor  B Bohr magneton g H proton g factor  N nuclear magneton  (0)  2 absolute value of the electron density at the nucleus squared

38.  1s = (  a o 3 ) -1/2 exp (-r/a 0 )

39.  1s (0)  2 = 1/  a o 3

40.  1s = (  a o 3 ) -1/2 exp (-r/a 0 )  1s (0)  2 = 1/  a o 3 a = 1420.4057 MHz

41.  1s = (  a o 3 ) -1/2 exp (-r/a 0 )  1s (0)  2 = 1/  a o 3 a = 1420.4057 MHz ca 21 cm

42. Historical Summary Fermi and Hargreaves calculated a in 1930

43. Historical Summary Fermi and Hargreaves calculated a in 1930 Rabi measured in lab 1949

44. Historical Summary Fermi and Hargreaves calculated a in 1930 Rabi measured in lab 1949 Van der Hulst suggested that this line might be detectable from space about 1945

45. Historical Summary Fermi and Hargreaves calculated a in 1930 Rabi measured in lab 1949 Van der Hulst suggested that this line might be detectable from space about 1945 Ewan and Purcell detected radio spectrum in 1951 Harry Kroto 2004

46. Doppler Shift  /  =  / = v/c  -v Blue shifted +v Red shifted  Harry Kroto 2004

54.  Sun Harry Kroto 2004

55.  Sun  1.6 H atoms per cc Harry Kroto 2004

57. E

58. E

59. a E

60. a b E

61. a b c E

62. a b c E

63. a b c E a’ Harry Kroto 2004

64. a b c E b’ a’ Harry Kroto 2004

65. a b c E b’ c’ a’ Harry Kroto 2004

66. a b c E b’ c’ a’ Harry Kroto 2004

67. a b c E b’ c’ a’ Harry Kroto 2004

68. a and b Blue Shifted c Red shifted - v 0 +v Intensity a b c Harry Kroto 2004

70. The data that indicate that the Milky Way is a Spiral Galaxy Harry Kroto 2004

71. The Doppler shifts not great enough to spatially resolve the clouds in this segment Harry Kroto 2004