Lewin's Challenge Image

Comments and questions about the APOD on the main view screen.
User avatar
Posts: 12
Joined: Wed Sep 29, 2004 7:28 pm
Location: Seattle, WA, USA

another photo

Post by wbeaty » Wed Sep 29, 2004 10:52 pm

Another photo of glass-bead rainbow
http://www.geocities.com/CapeCanaveral/ ... t.html#TLP


looks like polished stone to me

Post by jgallmeier » Thu Sep 30, 2004 5:24 pm

It looks like Dr. Lewin is standing over a slab of polished stone sometime around the middle of the day. The coating on the stone is reflecting sunlight giving the bright center and the coating is acting like a prism producing the rainbow of colors. I notice that the color order is opposite the glory photos posted.



Post by abc5 » Fri Oct 01, 2004 1:45 am

Is this similar to a previous Astronomy Image of the Day The Giant and The Glory?


Jim Bouton

Post by Jim Bouton » Fri Oct 01, 2004 12:03 pm

I rut in a answer early on,but I don't see it .I'll say it again,on a construction site there are a lot of oily spots on the ground.This a picture of one with the sun directly behind the photographer.the oil diffracts the light enough to cause the ring,in the picture or focal length.

Bob Peterson
Posts: 35
Joined: Sun Sep 19, 2004 10:47 am

Free Standing Glass Beads

Post by Bob Peterson » Fri Oct 01, 2004 2:04 pm

It should be apparent at this point that free standing glass beads on the pavement, with the sun as the source of light, have created the rainbow ring and bright area. How did the glass beads become free standing? The glass beads are placed in dispensers, to be applied to the wet paint creating retroreflective highway markings. The Prof is probably standing at a glass bead loading location, where it appears considerable spillage of the beads has taken place. Refer to my prior posts. The links posted in this thread re glass bead rainbows are very compelling. I changed my thinking as the evidence mounted.
Last edited by Bob Peterson on Fri Oct 01, 2004 2:58 pm, edited 2 times in total.


Identify the astronomy picture of the day

Post by Sandor » Fri Oct 01, 2004 2:30 pm

Some of the comments indicated the background had to be flat (beads scattered on

pavement, etc), but that is not necessary at all. In fact clues in the picture indicate

to me that Prof. Lewin took the photo in the direction of a dumped pile of particles. [Note the angular lines at the upper right and upper left of the picture, showing this to be a pile of material, and the non-uniformity of the light dispersion bears this out, as well.]
Other readers, such as jojojay, indicated the pattern should be eliptical, but such an elipse would only appear if the (planar) surface were viewed from a different, off-axis, angle. [In fact, on a non-uniform shape (or pile), would not be an elipse at all]
Anyway, the broad spectrum (white) light or sunlight comes from directly behind Mr. Lewin, hits reflective particles of grester than 0.3 mm in size (more likely 0.7 mm plus), much of the light reflects directly back at the observer (in this case the camera), resulting in the brighter central area, while the light reflected beyond a certain angle (deviation angle about 40 degrees) breaks into the rainbow effect. Beyond about 42 degrees the light is not reflected back at all, thus the area beyond the chromatic fringe is darker. The reason the particle size must be larger than the limit given is the lack of secondary or multiple "rainbows" which appear for smaller particle sizes down to about 0.01 mm (typical cloud or fog drop) or smaller where the colors overlap to the point where the color effect does not appear at all. Only if the particle size is greater than 1/3 mm. can we see red in the spectral ring, which we do in this photo. The chromatic dispersion effect relates to the size of the particles in relationship to the wavelength of the colors in question.

I have little doubt that the particle shape in question is spherical, but there are other shapes which would allow the phenomenon as well. When you shine a light into the inside corner of a cube, it will be reflected directly back towards the source, and a randomly tumbled pile could account for the dispersion in a ring, similar to that produced by spheres. However, the most likely item at a construction site to produce this effect is clear spherical beads as some others picked up on.

:D thanks,
"Dr. Dan"

Bob Peterson
Posts: 35
Joined: Sun Sep 19, 2004 10:47 am

Beadheads Win

Post by Bob Peterson » Fri Oct 01, 2004 4:19 pm

So, in conclusion, FREE STANDING GLASS BEADS IN COMBINATION WITH THE SUN AS THE SOURCE OF LIGHT is the WINNER. Thanks to all of you that have contributed to this obvious scenario. Here's another URL that explains the "Bright Area" inside the glassbeadbow:http://www.du.edu/~jcalvert/astro/heilig.htm
Last edited by Bob Peterson on Sat Oct 02, 2004 2:25 pm, edited 2 times in total.


I beg to differ about it being pavement paint

Post by jlfonz » Sat Oct 02, 2004 4:31 am

And as far as I know December 7th hasn't passed so I would have to assume that the good doctor hasn't let the genie out.

It looks rather obious to me that the object in the photo is a marble slate that is leaning upright. How would the good doctor get a picture like this otherwise? Was he laying on diving board while the sun is directly overhead?

He was probably walking by this construction site when he walked by the granite (or marble?) with the sun directly behing him. Sheets like these are shipped stacked on their edges and then polished when they get there. I'd wager that the "glass beads" that create the light image that has been well sussed out on the board, come from the friction of the sheets rubbing together during the shipping. That would explain what appears to be fingerprints distubing the layer.

I also considered the fact that it may also be simply morning condensation. Water molecules can cause the same effect just as easily.

I just had to put in my 2 cents.


construction site corona

Post by jarmstrong » Sat Oct 02, 2004 3:01 pm

I agree that this appears to be a solid-particle equivalent of a Glory, most probably caused by a spill of the glass beads (the sandy material on the ground) used to illuminate paint and traffic signs. The particles are perfectly spherical, have a fairly high refractive index and are a very uniform size, all conducive to the formation of this type of coronal effect. They are primarily used to produce corner-prism reflection, but their spherical shape would allow for coronal effects when they are not imbedded in a matrix (i.e paint).



The answer you have been looking for

Post by yogibear » Sat Oct 09, 2004 5:30 am

Strictly put it has to be a solareclipes in rear, with the camera angled correctly, you should get a straight symetrical path if done right. My opinion and if it is wrong it is something i totally have to try it out next time.


Posts: 1
Joined: Sat Oct 09, 2004 7:21 am

i had something like this happen today.

Post by stormdaile » Sat Oct 09, 2004 7:49 am

i saw something really similar..
i am a delivery driver and it is very humid here due to rain. i had some antifog on the windows but it rebelled and collects moisture and fogs. well it has now a nice layer of dust coating it that becomes a foggy opaque in the sun. i was not using a defrost and the setting sun came thru the front glass. i had on a pair of shooting glasses that i put the same stuff on tand they collected moisture and fogged too. out the front i saw the same ring appear. it was not like others because the rainbow was inverted. i saw this article sometime back and when i saw that to day i remembered this and thought id share my expereince. maby it will help find the answer. or then again it could have been a fluke...


very similar to this

Post by cgrinne » Tue Oct 12, 2004 11:07 pm

I saw the same effect when we were on an Alaskan cruise last summer. The fog was just starting to burn off and the sun was behind us about 9:00 AM. The shadows we cast from the railing into the still water next to the ship in the bay in front of the glacier caused the same diffraction pattern centered around our own shadows. The distance to the water was probably over one hundred feet so the center was not as brilliantly lit but I remember how fascinating it was to see.



Post by DavidByrden » Thu Oct 14, 2004 12:11 am

I want to comment on some things that were said. Apologies if I repeat arguments already made, I can't read all 22 pages.

The diffraction-through-a-hole idea: I've seen a lot of this in my daily life. Never had a coloured fringe.

The patch-of-oil idea: if the Prof were looking at a drop of oil spread on the ground, he would have to be directly overhead to make it appear circular. If so, the light source would have to be directly overhead, which the Sun does not do in Massachussets.

The shadow-of-a-wrecking-ball idea: Light rays from the Sun are parallel, so the shadow of a wrecking ball would have the same size no matter how far away it was, so the Prof could never cover it with his head.

The camera-flash idea: nice, but why would anyone place a camera flash unit BEHIND their own head, and why do it on a grimy construction site, and why ask us about it?

Someone said "not enough particles to create a glory in this short distance". In fact you can get a good rainbow with a small garden sprinkler, because it puts out a much higher density of water than a mist or cloud. If these are glass surfacing beads, as many suggested, there is no problem having enough of them on a wall or the ground to make a rainbow.

The bright area within the circle: not a problem. This is a standard feature of rainbows.

Surface is not perpendicular: not a problem. After all, you see perfect rainbows in clouds that are not flat or perpendicular to you! Since each droplet reflects light from the sun to you, and the sun is effectively at infinite distance, the distance of the drops (or glass beads) is irrelevant. You will see a circle even looking at level ground from an angle (which the Prof is doing).

Ice particles: you need circular particles to make a uniform circular rainbow. Ice particles would be too angular. I don't know if fine-grit construction sand would fit the bill.


Just taking a guess

Post by emarts » Tue Oct 19, 2004 8:08 pm

Looks like he's standing outside a car wash or something. Those look like soap bubbles on the ground and there's a fine mist causing the rainbow affect. The sun is directly behind him. His head is in the center of the circle. To see a rainbow one must stand directly in front of the sun. You would only see half the rainbow as the bottom half would follow beneath the horizon. In this case the nearly entire rainbow is visible because the mist is surrounding the viewer and there's nothing obstructing his view. The brightness in the center is consistent with rainbows.



Circle of light around photographer

Post by WhimpeyD » Mon Oct 25, 2004 7:14 am

This happened to me in Kauai - Jan '04. I took an 8mm film motion picture of the effect. This is what happened:

I was looking at clouds from the cliffs above the Napali coastline when I noticed I could see my shaddow on the clouds. (Sun was behind me.) Around my shaddow was a perfect rainbow in the shape of a circle - like in the posted picture. I rolled my camera on it & it came out on film too. Every color of the rainbow circled around my shaddow. I thought it was the same effect that happens when we see rainbows, except this wasn't an arch, it was a perfect circle around my head & shoulders.

Why could I see that? And just like with rainbows, it appeared to move with me when I did. (Like when the sunlight on water appears to move with you if you walk beside it.)


Post by Guest » Sun Nov 14, 2004 5:16 pm



Post by Anthony » Mon Nov 15, 2004 12:24 am

SimplySeven wrote:I am a Boeing 707 pilot and I see these rings on a regular basis whenever I go fly. It normally occurs on a bright sunny day when the shadow of my jet is cast on a flat blanket of clouds a few thousand feet below me. If the clouds are close enough, the outline of my jet can be quite crisp, but as the clouds become more distant the shadow will eventually disappear and actually become the brightest point in the middle of the colored rings. I always figured it is kind of like a magnifying glass/concave lens. If you put an object directly between a lens and the surface where its light is cast you can still completely eliminate the objects shadow when placed at the right distance. So, you may ask how does an airplane act as a lens? Well, it doesn't, it is like a prism. Since the light is cast all the way around my jet the result is a circle, much like a lens. And since the light is dispersed like it would be by a prism the resulting colors of violet, blue, green, yellow, orange, and then red can be seen. The colors in Prof Walter Lewin's picture aren’t so identifiable because of the poor surface of which he took the picture on. However, on a pure white cloud the colors are much more crisp. If you look very closely at the professor’s picture though, the colors are all there. No light other than the Sun's is used and no photographic tricks or special materials were implemented.
I have seen the exact same effect once, while on an airplane a couple of months ago. At first I thought it was caused by the window glass, or that there was something wrong with my eyes. So I moved around to check if the "halo" changed position relatively to the window. It did, so I thought it could not be the window that caused it. I also checked from another window to double check At first I noticed it on the clouds below (I can't figure how much lower the clouds were). Yet this is exactly what I saw, a very subtle "halo" centered around the plane's shadow. I could also see the effect on the ground, although it became *much* more difficult. I had to focus somewhere else instead of where it actually was. What puzzled me was that if the plane acted as some kind of lens or prism it would be very strange, given the irregularity in the plane's shape. Yet the halo seemed perfectly round.

Anyway, I never got to find how this effect happened. Next thing I know I stumble by accident on this post :-)


another view

Post by trak0r » Tue Dec 07, 2004 7:49 pm

It looks like your taking this picture while facing a mirror or window, with the sun directly behind you head. You used very fast film, low grain quantity, to get the effect that you have in the surrounding area that you see (either the reflection or through the window reflection or direct view (can't tell). You probably didn't change the exposure of the film or digital camera settings at all except maybe reduce the brightness or use an F stop of like 28 or higher to reduce the amount of light that was able to get into the camera; and as a result you have a silhouette. The colored rings that we see are the same effect that you get with lens flare, or like a rainbow. The light bends at different angles depending on which wavelength it is in any medium, glass in this case, water in the rainbows. The fact that it is a circle rather then an arc is do to the fact that there isn't much of an angle if any because it is directly behind you 180 degrees? the fact that it is lighter in the middle of the circle compared to the outer is because the angle of the lens, which caused the spectrum is less then the 22 degrees or whatever it needed to be to cause the spectrum in glass in the first place, and the therefore you have greater transmission of photons and the darker is the opposite.

- trak0r

S Bilderback

My best guess

Post by S Bilderback » Wed Dec 08, 2004 1:14 pm

I know it is the 8th but I don't se a solution posted so here I go.

I looks to me like a single direct light source (the Sun) projecting through a relatively small opening in the shadow of a structure at distance explaining the brightness and symmetry of the circle, I don't remember my refraction equations well enough to know if the refracted light at the perimeter is caused by something at the light source, the thickness of the obstruction or what it's made from, or my better guess is sandblasting residue coating the ground causing the refraction.


Post by Scooby108 » Thu Dec 09, 2004 7:50 pm

I didn't feel like reading ALL 22 pages of posts, but could this be caused by the viewfinder of the camera? The camera taking the picture has a wideangle lens, so when you look through the viewfinder, the scene you see looks smaller. Look through the opposite end of the viewfinder and what you see looks bigger. So, the light from the sun going through the viewfinder is basically passing through a magnifying glass. The bright center of the ring is an image of the Sun that is out of focus (we all know what happens to ants when it is IN focus). Prismatic effect is so pronounced because the use of low quality optics in the viewfinder.


It's the sun being projected through the camera's viewfinder

Post by onus » Thu Dec 09, 2004 8:05 pm

You've got a camera with a viewfinder on it. It's projecting the sun onto the pavement in a circular pattern due to the lens itself.

I'm not sure about the order of the colors.


Post by Guest » Thu Dec 09, 2004 8:05 pm

Ooops, I didn't see Scooby's post.

I agree with what you said!



A comparable 'mystery picture'?

Post by DDAVIS » Fri Dec 10, 2004 6:12 pm

The APOD image reminded me of an old photographic mystery I have held onto for nearly 30 years. A photo taken by a friend simply to finish off a roll of film contains some odd streaks I at first dismissed as shadows of hairs inside the camera. Upon close inspection the streaks seem to disappear into and behind buildings in the view. I will probably never know what the photo shows, although if anyone familiar with B&W photography has encountered something similar 'artifacts' which are somehow a 'by product' of the medium I would like to hear about it.

Don Davis


a Glory ?

Post by Georg » Tue Dec 14, 2004 3:10 pm

I forgot about the deadline but did not find an answer either so... I think this is a wall or angled wall with dew on it . Semispherical water droplets reflect the sun's light back to the camera in the center. Further away from the center only refracted and reflected light reaches the lens therefore the colors. Beyond the colors the angle is to large for light to reach the camera.
I would say, something very similar if not a glory.

Georg L

S. Bilderback

Post by S. Bilderback » Fri Dec 17, 2004 11:42 pm

Is someone going to post the answer or tell me where I might find it?