A classic inferior mirage

October 25, 2000


Provided by: Pekka Parvianinen, Turku University
Summary authors & editors: Jim Foster

Because October is generally a fair month across much of the US and Europe, it's a nice time of year to be on or near the water. Mirages are commonly seen on many water bodies if clear skies and calm winds prevail. The above photograph was taken by Pekka Parviainen, a lecturer in mathematics at Turku University in Finland. It's a classic example of an inferior mirage. With an inferior mirage, the image of a distant object is always displaced downward. When the water is warmer than the air, as it often is in the autumn, a ray of light traveling through the air will be bent or refracted upward. The light rays are more noticably bent nearer the water surface than farther above it since the thermal gradients are stronger near the water surface (light refracts toward the more dense medium). So, a ray of light that enters your eye from the direction of the water in the distance, may actually have originated higher up in the sky. Notice in the above example that below the lighthouse and ship you can see a mirage of the sky as well as their inverted images - its inferior mirage.

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