Starship Asterisk*

One last thought. A lot of people have been talking about the angle of defraction and quoting specific numbers. Anyway the angles typically specified are for WATER to AIR interfaces. There are different values for GLASS to AIR, OIL to AIR, ETC to AIR.

I should have been more emphatic in my first post. I have seen this optical effect many times. There is nothing magical about it. We use a small sand blaster at work to clean parts. We do it outside on a cement slab. The silica sand grains are quite small and produce the wonderful halo effect when well lit by sunlight. The rainbow ring at the margin of the shining center is a strong part of the optical effect when viewed in person. Try it for yourself some time if you get a chance. It really is a wonderful sight. The simplest explanation can be easily tested.

I saw something like this when I had my car washed at a gas station and the door of the washing bay wasn't closed. The sun was just behind me when I looked at the center of the (brightest) rainbow ring, and a cloud of fine water droplets was coming towards me, where the size of the droplets could have been quite similar for all of them.
The dark background of the photo seems to be an asphalt covering, which could also have been wet, making the faint ring visible enough for a clear photo.
Moreover, if I remember correctly then I also noticed that the area within the ring was brighter than the area outside, but not as pronounced as in this picture. Perhaps some kind of polarizing filter?

M guess is that we're looking at some spilled glass beads of the kind used in road stripe paint. Clearly, the sun in directly behind the photographer and the white area in the center is sunlight reflected back to the photographer via total internal reflection in the beads. Total internal reflection inside the beads as well as imperfections in the bead surface, etc, will give rise to a relatively uniform "bright spot". The edge color is simply a mini-rainbow created by the beads at the edge of the total internal reflection cone (I estimate a cone half angle of about 20-25 deg, based on a 5.5' photographer and a rough estimate of the size of the shadow). Violet is on the inside, red on the outside due to the higher index of refraction for shorter wavelengths, just like a rainbow.

I have seen this phenomenon once in my life. I was in a hot air balloon over the Central Valley of California not long after sunrise. The sun was behind me and the shadow of the balloon on the rows of dew-moistened tomato plants below was surrounded by a halo of light and color. It was astonishing. I took pictures of it and my brother explained the phenomenon to me.

Is it an ordinary rainbow, in droplets of dew standing on the ground (water-repellant, maybe?).

The color order is right, and the angular dimensions of the arc, the bright interior and dark exterior are like an ordinary rainbow.

kilo*man, Ann Arbor wrote:Directly behind the photographer are two (or more) small apertures which are close together and through which a bright light is shining (perhaps the sun?). The apertures acts as lenses to focus the image of the bright light upon the surface that is being photographed. Thus the image of the light source is brighter than the surrounding dimly lit surface. The color rings are due to the diffraction patterns from the apertures interfering with one another and producing maxima for each wavelength.

I submitted my guess before reading any of the postings. The guess above is the closest I've seen to my guess.

There's only one hole. The sun is the light source. The central bright circle is the image of the sun focused by the pin hole which is behind the professor.

The color sequence is caused by diffraction with the edge of the hole. It's the opposite sequence seen in a "Glory".

What I did not originally guess about was the medium the hole is in. After reading someone's posting concerning visqueen (plastic) I'm convinced that the hole is in a transparent, or translucent medium.

Basically, the professor is standing in a camera obscura that uses a pinhole lens. The lens is a large distance from the focal plate and the hole is relatively large. I hadn't considered a translucent or transparent medium for the hole to be in, but that would explain the high illumination outside of the focused image of the sun.[/b]

Go to http://www.wunderground.com/history/air ... story.html for June 20, 2004 weather history. Snow! Not likely. Ice! Not unless liquid nitrogen was dumped (shades of the terminator).

This is an example of Heiligeschein.

when I got over the clouds hang gliding I saw this effect as a brilliantly lit wing shadow surrounded by a rainbow.
http://home.earthlink.net/~gamma-quadra ... lying.html

I'd go with the whitish granular substance for photo explanation.
whatever it is, it appears to be spilled on asphault - which is the next best clue - road contruction material used as a paint additive.

Could this just be an ordinary rainbow, it is at the antisolar point, there is no refrence as to how many degrees it spans, although it looks a little small, but this could have been a wide angle shot. The center is lighter than the outside though again suggesting this might just be an ordinary rainbow, pluss the colors are the same direction as with an ordinary rainbow

RJD in Dallas wrote:A circular diffraction pattern. Instead of sunlight, the source of light is the camera flash.

now that's kind of funny..how do you explain the shadow of the person taking the photo then? LOL..obviously the source of light had to be behing the person. it is the sun.

this phenomeno is very well known and commonly seen from airplane.

It is called a Broken Spectre. Now what was on the ground to cause that diffraction? that is the question. glass particles? ice? not in June I am guessing.

The professor is wearing one of those Ossam Bin Laden hats

http://images.ibsys.com/2003/0910/2469786_200X150.jpg

raze wrote: What I did not originally guess about was the medium the hole is in. After reading someone's posting concerning visqueen (plastic) I'm convinced that the hole is in a transparent, or translucent medium.

If that'S the case, then this is not a natural occurence but it is just a trick done with photographic equipement..no interest if that is the case.

Lot's of smart folks have suggested that glass beads are responsible for the optical treat. The sand-blasting suppliers rely on sources of sand that are nearly pure silica or glass. The bead size is quite small. I'd guess that it is less than half a mm. A layer of it is hard to stand up on. After you pour some out on concrete at about noon tomorrow if the sun is shining and take your photos, take a little run at it and try to be gracefull.
Cal

Yo professor so fat that light bends around him....

haha just kidding, 13 pages and couldn't let that one pass

Could there be light reflecting back through the camera eye piece in some strange way?

Since the coloration is the familiar one of the rainbow, it seems evident that sunlight is reflecting from the far side of transparent droplets Where might these droplets be? The most likely location is in the surface, which quite likely has glass beads put down by highway authorities seeking to increase the reflectivity of the roadway.

He is standing in front of a big pile of dirt. There is someone arc welding behind him. He catches a picture of his shadow on the big pile of dirt just as an welding flash goes off. It's cold but misty so there is a rainbow.

Anyway, just a guess.

It's a simple laser beam. You can get the same effect when sunlight shines directly through a peep hole on a door. If the sun was in eclipse during the shot, the cirle shape would take on the shape of the eclipsed sun.

i have gotten the same effect when i was a lighting designer in the theatre. the shadow in the center is well defined, but you move from spot focus towards flood focus. that causes the edges of the bean of light to change the way they have. usually have produced this effect with an ellipsoidal instrument, no gel or diffusion.

the previous post was from me, but i wasn't logged in. ROFL
sorry for the double posting

Actually, given the even-spread of the 'halo', and, the unlikely event that the phenomenon exists only because of the camera's lens or the photographer's presence, that the halo is related to reflective paint doesn't work. The paint isn't evenly spread and would diffuse too much light back to the viewer.

The brightness in the center is, nonetheless, likely due to something reflective splashed all over the pavement, but the halo comes from behind the photographer.....

.... probably from a concave (as seen from the pavement) transparent (or miniminally opaque) "bubble" of glass or plastic. The "bubble" would be acting like a lens (or series of lenses) causing the halo. The focal point of the 'lens' is somewhere beyond the pavement's surface so that the light has not yet come back together (good thing or the photographer might be feeling very much like an ant under a kid's magnifying glass!).

The color shift at the edges is probably due to wet pavement. Whether wet from water or a petrolium-based product (or both) would require a quick analysis from some far more versed in spectral analysis than myself.

This is my guess, The bright circle is caused by sunlght reflected off the bright pavement and back out the open camera shutter and lens. The colors are caused by the layer(s) of coating on the lens surface.

Obviously a ghost with rainbow colored hair. Simple! Voi la!