The Aureole Effect, and Why It Makes You Look Like an Angel

What we see here is a picture taken off a pier in beautiful San Francisco. At the bottom middle, you can see the shadow of the photographer's head. At the top right there's a sea lion hoping that the photographer will drop a corn dog or something. Between the two there's a semi-circular explosion of sunbeams seeming to come up from under the water. This is known as water aureole, or the aureole effect, and it needs a few things to happen to let us see it.

First of all, the water's surface can't be still. Anyone who's ducked under a swimming pool surface has seen the ripples of light and dark that appear as soon as the pool's surface is agitated. The waves act as lenses to focus light at certain points. Those patterns of light and dark form the rays that you're seeing in water aureole.

Second you need slightly dirty water - dirty in the sense that there are tiny pieces of grit in it that will scatter the light upwards towards your eye. These let you see the path of the rays of sunlight, the same way dust floating in a darkened movie theater will let you see the path of the light from the projector.

And last you need the sun directly behind your head - or your camera. The rays don't really stream out from your brilliant noggin. The beams of sun are all pretty much parallel to each other, but when you look directly down them with the sun behind you, they look like they're arching out in all directions. It's a little like driving past an orchard full of straight lines of trees. Look directly into the trees as you pass and it will look like they're fanning out in diagonal lines to either side of your gaze. If you're not adventurous enough to get outdoors, you've probably also seen this in a tub, or in the bathroom or kitchen sink. Just get the light right, and look at your own halo.

Image: Brocken In a Glory

Via Atmospheric Optics and Color and Light in Nature.