Atmospheric Illusions

[RoDaSm]

Lie on the ground on a hot day and the legs of cattle in the distance seem to shimmer. In fact most things close to the ground in the distance seem to shimmer. Could someone explain to me what this is and what it is caused by? It is a form of refraction but there is a special name for it.

[swansont]

Lie on the ground on a hot day and the legs of cattle in the distance seem to shimmer. In fact most things close to the ground in the distance seem to shimmer. Could someone explain to me what this is and what it is caused by? It is a form of refraction but there is a special name for it.

 

Atmospheric refraction. I don't know if there's any more special name for the phenomenon. It's from the varying density of the air, basically from turbulence; in this case from the ground heating the air above it. Refractive turbulence is a problem for astronomers using terrestrial telescopes..

[Acme]

Lie on the ground on a hot day and the legs of cattle in the distance seem to shimmer. In fact most things close to the ground in the distance seem to shimmer. Could someone explain to me what this is and what it is caused by? It is a form of refraction but there is a special name for it.

The special name is mirage. More specifically, heat haze or heat shimmer, a type of inferior mirage.

 

mirage @ Wiki: >> http://en.wikipedia.org/wiki/Mirage

...

Heat haze

 

Heat haze, also called heat shimmer, refers to the inferior mirage experienced when viewing objects through a layer of heated air; for example, viewing objects across hot asphalt or through the exhaust gases produced by jet engines. When appearing on roads due to the hot asphalt, it is often referred to as a highway mirage.

 

Convection causes the temperature of the air to vary, and the variation between the hot air at the surface of the road and the denser cool air above it creates a gradient in the refractive index of the air. This produces a blurred shimmering effect, which affects the ability to resolve objects, the effect being increased when the image is magnified through a telescope or telephoto lens. ...