Aureole effect
Encyclopedia
The aureole effect or water aureole is an optical phenomenon
similar to Heiligenschein
, 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 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
, 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.
Optical phenomenon
An optical phenomenon is any observable event that results from the interaction of light and matter. See also list of optical topics and optics. A mirage is an example of an optical phenomenon....
similar to Heiligenschein
Heiligenschein
Heiligenschein is an optical phenomenon which creates a bright spot around the shadow of the viewer's head. It is created when the surface on which the shadow falls has special optical characteristics. Dewy grass is known to exhibit these characteristics, and creates a Heiligenschein...
, 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 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
Antisolar point
The antisolar point is the imaginary point on the celestial sphere exactly opposite the Sun. It is where anticrepuscular rays appear to converge, and on a moonless night away from city lights, it is often possible to see the gegenschein there. The apex of a rainbow will also form roughly 42...
, within the viewer's shadow.
As in similar antisolar optical effects (such as a glory
Glory (optical phenomenon)
A glory is an optical phenomenon that resembles an iconic saint's halo about the shadow of the observer's head. The effect is produced by light backscattered towards its source by a cloud of uniformly sized water droplets...
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.