To show how air currents cause the "twinkling" of a star.
Laser cart with hot plate.
A laser beam is directed on a distant wall or screen. When the heater is positioned below the laser beam, hot air convection currents and density changes cause the beam to move continuously, or "twinkle."◙
Jay S. Huebner and Terry L. Smith, Why Magnification Works, TPT 32, 102-103 (1994). Jay S. Huebner and Terry L. Smith, Letter: More on Twinkling, TPT 32, 263 (1994).