| MadSci Network: Physics |
The phenomenon you observed is due to variations in air density as the warmer air streams into the cooler air outside the car. Light is refracted or reflected as it passes from air at one density to air with a higher or lower density. If the door is left open long enough and the temperature of air inside the car equalizes with the temperature of air outside the car (not likely if the car is parked in the sun), then the streaming of warmer air into cooler ceases and the phenomena is no longer observed. The effect is related to that of mirages observed over hot desert surfaces, though in that case it's a warmer layer of air near the surface that gives rise to the mirage. Two excellent references for learning more about this type phenomena are the following: Page 45, and pages 63 to 66 of M. Minnaert's The Nature of Light & Colour in the Open Air, Dover Publications, 1954, sbn 486-20196-1. Page 63 of M. Minnaert's Light and Color in the Outdoors. Springer-Verlag, 1992, isbn 0-387-94413-3
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