8B30.20 - HR Diagram

Credit for the picture and explanation: ESO ( European Southern Observatory).
Credit for the picture and explanation: ESO ( European Southern Observatory).
Code Number:
Demo Title:
HR Diagram
Area of Study:
Stellar Astronomy
Opaque Plexiglass plate, diffraction grating, Overhead Projector.

(1)  Set up your basic overhead projector with a piece of diffraction grading film on the reflector at top with two solid moveable black poly carbonate pieces for your slit. (2) The classic result is a spectrum, but choose the one with Violet to the left side on your screen as opposed to the red on the left one would normally do.  (3) widen your two black pieces so your slit now is projecting overlapping rainbows, so to speak, and you no longer have green in the center.  This will help explain why we see no "green" stars and why our green sun appears white in space.  (4) With the white in the center now I can put markers or arrows on the screen if it is magnetic, and lecture about the HR diagram and track the lifetime of stars. 

Credit for the picture and explanation:  ESO ( European Southern Observatory).  

In the Hertzsprung-Russell diagram the temperatures of stars are plotted against their luminosities.  The position of a star in the diagram provides information about its present stage and its mass.  Stars that burn hydrogen into helium lie on the diagonal branch, the so-called main sequence.  Red dwarfs like AB Doradus C lie in the cool and faint corner.  AB Dor C has itself a temperature of about 3,000 degrees and a luminosity which is 0.2% that of the Sun.  When a star exhausts all the hydrogen, it leaves the main sequence and becomes a red giant or a supergiant, depending on its mass (AB Doradus C will never leave the main sequence since it burns so little hydrogen).  Stars with the mass of the Sun which have burnt all their fuel evolve finally into a white dwarf (left low corner).

  • H. Hauptmann, F. Herrmannm and K. Schmidt, "The Transformation of a Main Sequence Star into a Red-Giant Start in the Core-and Shell Model", TPT, Vol. 68, # 5, May 2000, p. 421.
  • Christopher L. Mulliss, "Teaching the Main Sequence", TPT, Vol. 34, # 6, Sept. 1996, p. 327.
  • Emilia P. Belserene, "Response", TPT, Vol. 27, # 4, April 1989, p. 231. 
  • David L. Mott, "Aging Stars", TPT, Vol. 27, # 4, April 1989, p. 231. 
  • Emilia Pisani Belserene, "Can We Watch the Stars Grow Older?", TPT, Vol. 25, # 7, Oct. 1987, p. 420.
  • Henry Albers, "It's the Temperature, Not the Composition", TPT, Vol. 18, # 1, Jan. 1980, p. 10.
  • Claudine Carlton, "Stellar Evolution and Cosmology in High School Physics", TPT, Vol. 17, # 7, Oct. 1979, p. 460. 
  • Robert T. Deck, "Comments on 'Why is the Sun So Large?'", AJP, Vol. 74, # 1, Oct. 2006, p. 10.
  • D. J. Mullan, "Why is the Sun So Large?", AJP, Vol. 74, # 1, Jan. 2006, p. 10.
  • H. Hauptmann, F. Herrmann, K. Schmidt, "The Transformation of a Main Sequence Star Into a Red - Giant Star in the Core - Shell - Model", AJP, Vol. 68, # 5, May 2000, p. 421.
  • M. Maercker et al., "Deciphering a Star's Spiral Shell", Back Scatter, Physics Today, Dec. 2012, p. 92.
  • D. Tattersfield, "7.25, The Hertzsprung-Russell Diagram", Projects and Demonstrations in Astronomy, p. 171.
  • Janice VanCleave, "Demonstrate Why Stars of the Same Luminosity Can Appear to Be of Different Brightness", Super Science Challenges, p. 15.
  • Janice VanCleave, "Winter Colors", Constellations for Every Kid, p. 208.

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