The word ‘Aureole’ means the light that surrounds something; just like in movies when we see some holy body, the light radiating from the backward of that holy body can be related to this effect. The aureole effect can also be called the ‘water aureole’ which is basically an optical phenomenon. It is just similar to ‘Heiligenschein’ which is a German word for aureole. Aureole is said to be a bright illuminated area that is surrounding a source of atmospheric light (it may be the Sun) when the light is allowed to travel through a medium containing particles of many sizes or droplets that are much large when compared to the wavelength of the light.
The primary Aureole effect refers to creating a very sparkling light and dark rays that we can usually see radiating from the shadow over the viewer’s head. This effect is seen only over a rippling water surface or any water surface that is in slight motions and has the formation of ripples. The waves here, act as lenses to focus and to defocus the sunlight.
Focused sunlight often produces what we call as, lighter rays. While if we talk about the defocused rays of the sunlight, then they produce what we call as the darker rays. The aureole effect becomes much more noticeable than before due to the presence of suspended particles, this is because of the fact that suspended particles often reflect the rays of Sunlight when they fall on them. So here the presence of suspended particles inside the waterbody helps to make the aureole effect more pronounced. This effect is at a greater angular distance when seen from the viewer’s shadow when the viewer is at a higher level above the waterbody, and it can sometimes be seen from a plane.
We know that rays travel in a straight line under normal prevailing conditions. Same is the case here, the focused ray cones that are the lighter ray cones, are actually more or less somewhat parallel to each other. The rays of the aureole effect appear to be coming out from the shadow of the viewer’s head due to several viewing effects. Since the viewer’s line of sight is parallel, so if seen from the viewer’s perspective, these rays seem to be radiating somewhere from the point opposite to the direction of the sun (also called as Antisolar Point) within the viewer’s shadow.
It is interesting to know that in such a kind of antisolar optical effect, each observer will observe an aureole effect radiating only from their own shadow of the head. Same is in the case where a photographer holds his camera at the length of their arm, the aureole effect that appears in the picture will be seen just coming out from the shadow of his own camera. But in this case, the photographer would still see the aureole effect around the shadow of their head while taking a picture. This generally happens due to the reason that the aureole effect is always seen directly opposite to the sun, centered somewhere at the antisolar point. If we look at the antisolar point then the point itself is located within the shadow of the observer. When we try to take the picture of aureole effects from a plane, it becomes possible for us to tell where the photographer was seated by looking into the picture for this antisolar point.
The aureole effect needs a few things to be seen, first, the water’s surface should not be still. It does not mean that for the effect to be seen there should be running water but the water should be in such a state that it should be neither running nor still which means it must show ripples. Anyone who jumps inside a swimming pool or if any time when we through the stone on the surface of the water, ripples can be seen. These are of light and dark waves that appear as soon as the surface of the water is agitated or disturbed. These waves act as lenses to focus light on certain points. These patterns of light and dark form the rays that you seeing anytime in a water aureole whenever the surface is disturbed.
One second condition that is needed for this effect to be observed is slightly dirty water which means that their tiny pieces of dust or girt should be present in it. These tiny particles allow the light to scatter and reach upwards towards our eye. When sunlight or any other source of light strikes the particles, the part of the sunlight becomes visible just in the same way as the floating dust particles in a dark movie theater lets you see the path of the light from the projector.
The last condition for this effect to be observed is that the sun or the source of light should be exactly in the opposite direction of your head or camera (in case you are capturing the effect). The rays of the light don’t really stream out from your head. The rays of light or may it be the beams of the sun, all are parallel to each other, but when the sun is in the opposite direction as you (the sun is behind you) and then you look directly down to them they will appear to you like they are coming out in all the directions. This phenomenon can also be seen in the household, for example when we see a bathtub full of water in the bathroom or in a kitchen sink. The aureole effect is a very interesting phenomenon and may also be used in those areas where photography at different light angles or at different levels of creativity of light is to be considered.