6A40.47 - Refraction - Twinkling Planets and Stars

Code Number:
Demo Title:
Refraction - Twinkling Planets and Stars
Change of Refractive Index with Temperature
Area of Study:
Laser, Hot Plate or Grill Lighter, and Screen.

Shine the laser on a distant wall or screen. Place a hot plate or the grill lighter directly under the beam and close to the laser. The image of the spot on the wall will be be steady until heat is applied after which it will appear to move, shimmer, and twinkle. This is due to the change in refractive index of the air through which the beam moves. The same effect takes place when viewing stars through the atmosphere.

A second effect is also observable.  Mark the place on the wall where the laser beam spot is initially.  Then move the hot plate under the laser beam.  You will observe that the laser spot moves very visibly upward due to traveling through the less dense hot air above the hot plate.  

  • Lorne Whitehead, John Huizinga, and Michele Mossman, "Why do Stars Twinkle, and do they Twinkle on Mars?", AJP, Vol. 80, #11, Nov. 2012, p. 980. 
  • C. L. Enloe, M. L. Brake, and T. E. Repetti, "Laser Deflection Through a Spark", AJP, Vol. 58, #4, Apr. 1990, p. 400.
  • Lauren Richey, Bailey Stewart, Justin Peatross, "Creating and Analyzing a Mirage", TPT, Vol. 44, # 7, Oct. 2006, p. 460.
  • Daniel Engber, "Why Do Stars Really Twinkle?", Popular Science, Vol. 287, #5, Nov. 2015, p. 65.
  • James C. Kernohan, "Astronomy Demonstrations: 5. Twinkling of Stars", PIRA News, Vol. 9, #3, Jan. 1995, p. 22.
  • "O-226. Laser Dance Across Hot Plate", DICK and RAE Physics Demo Notebook.
  • "O-225. Star Twinkle with Hot Plate", DICK and RAE Physics Demo Notebook.
  • Jearl Walker, "6.33, Shadow Bands", The Flying Circus of Physics Ed. 2, p. 254 - 255.
  • Jearl Walker, "6.32, Shimmy and Twinkling Stars", The Flying Circus of Physics Ed. 2, p. 254.
  • Julien Clinton Sprott, "6.4. Twinkling Stars", Physics Demonstrations, ISBN 0-299-21580-6, p. 240 - 241.
  • Janice VanCleave, "73, Twinkling Star", Janice VanCleave's Astronomy for Every Kid, p. 158 - 159.
  • Janice VanCleave, "23, Twinkling Star", Janice VanCleave's 202 Oozing, Bubbling and Bouncing Experiments, p. 15.
  • M. Minnaert, "44. Shadow Bands", Nature of Light and Color in the Open Air", p. 71 - 73.
  • M. Minnaert, "43. Scintillation of Planets", Nature of Light and Color in the Open Air", p. 70 - 71.
  • Sara Stein, "The Sun Appears Before It Rises", The Science Book, p. 192.
  • Julius Sumner Miller, Q214 & A214, Millergrams II – Some More Enchanting Questions for Enquiring Minds, p. 65 & 113.

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