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The aureole effect or water aureole is an
The aureole effect or water aureole is an optical phenomenon
Optical phenomena are any observable events that result from the interaction of light and matter.
All optical phenomena coincide with quantum phenomena. Common optical phenomena are often due to the interaction of light from the sun or moon wit ...
similar to Heiligenschein
(; ) is an optical phenomenon in which a bright spot appears around the shadow of the viewer's head in the presence of dew. In photogrammetry and remote sensing, it is more commonly known as the hotspot. It is also occasionally known as Cellini ...
, creating sparkling light and dark rays radiating from the shadow of the viewer's head. This effect is seen only over a rippling water surface. The waves act as lenses
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
to focus and defocus sunlight: focused sunlight produces the lighter rays, while defocused sunlight produces the darker rays. Suspended particles in the water help make the aureole effect more pronounced. The effect extends a greater angular distance from the viewer's shadow when the viewer is higher above the water, and can sometimes be seen from a plane.
Although the focused (light) ray cones are actually more or less parallel to each other, the rays from the aureole effect appear to be radiating from the shadow of the viewer’s head due to perspective effects. The viewer's line of sight is parallel and lies within the cones, so from the viewer's perspective the rays seem to be radiating from the antisolar point
The antisolar point is the abstract point on the celestial sphere directly opposite the Sun from an observer's perspective. This means that the antisolar point lies above the horizon when the Sun is below it, and vice versa. On a sunny day, t ...
, within the viewer's shadow.
As in similar antisolar optical effects (such as a glory or Heiligenschein), each observer will see an aureole effect radiating only from their own head’s shadow. Similarly, if a photographer holds their camera at arm's length, the aureole effect appearing in the picture will be seen radiating from the shadow of the camera, although the photographer would still see it around their head's shadow while taking the picture. This happens because the aureole effect always appears directly opposite the sun, centered at the antisolar point. The antisolar point itself is located within the shadow of the viewer, whatever this is: the eyes of the viewer or the camera's lens. As a matter of fact, when aureole effects are photographed from a plane, it is possible to tell where the photographer was seated.
See also
*Gegenschein
Gegenschein (; ; ) or counterglow is a faintly bright spot in the night sky centered at the antisolar point. The backscatter of sunlight by interplanetary dust causes this optical phenomenon.
Explanation
Like zodiacal light, gegenschein is su ...
* Retroreflection
A retroreflector (sometimes called a retroflector or cataphote) is a device or surface that reflects radiation (usually light) back to its source with minimum scattering. This works at a wide range of angle of incidence, unlike a planar mirror, ...
* Subparhelic circle
The subparhelic circle is a rare halo, an optical phenomenon, located below the horizon. It passes through both the subsun (below the Sun) and the antisolar point (opposite to the Sun). The subparhelic circle is the subhorizon counterpart to the p ...
* Sylvanshine
References
{{Reflist Atmospheric optical phenomena