Lewin's Challenge Image

[pez]

I believe this is the refraction phenomenon known as a Glory, more commonly seen as a circular rainbow around the shadow of an aircraft on clouds below. Normally the refraction is caused by same-size water vapour particles. In this case, I believe it must be something like those reflective beads used in road markings. As for the brighter appearance inside the circle, I'm going to guess that it has something to do with diffraction about the opaque object (Dr. Lewin).

[Ka-Spel]

I used to work at a fiberglass plant. In the parking lot at night you could see halos on the ground around each street light.
I think the guy who said it was the fine glass beads is correct.
Afterall, 'construction site' is the main clue and would be a source of the materials needed.
Khataclimichi

[javaguy78]

It seems to me that it is a perfect example of the Glory.

I once had the same effect in Estes Park, Colorado in a motel. I took a really hot shower, causing the mirror to fog up. The incoming light from the window from my back reflected off the foggy mirror and into my eyes. I saw two rings, one around each eye in the foggy reflection. I have determined that it was only mine that I could see, because I called someone else in and they could see their "Spectral Rings" but not mine and vice versa. I can repeat the experiment flawlessly by fogging up a mirror and standing opposite a window. It seems to only work with natural light.

I believe the glory is the same thing. Only the person it is happening to can see it, except you can take a picture of it... where as my "Spectral Rings" cannot.

My conclusion is it is a refraction of light caused by high humidity levels. The himidity in the hot shower room caused the refraction of light in my eyes, and the glory seems to be caused by refraction of light through water dropplets surrounding the spectator. I have never witnessed the Glory in dry areas such as the rocky mountains, but I have seen the same thing in Miami on the sidewalks.

If someone can help me out with my Spectral Rings in the eyes, please feel free to contact me at cschalk@hotmail.com

[interstellarmichael]

this is a glory. it essencally the opposite of a rainbow. the winter morning sunlight frequently comes thru the peephole on the front door and makes a ring of colors with a shadow in the center on the wall above the fireplace. that is a rainbow. a glory has the opposite color sequence and is bright in the center. i saw a glory while i was in a jet once. however, this has not been an explanation, only an identification.

[sbellis]

I have noticed a similar bright ring when walking my dog at night under a bright street light on dew-covered grass.
1. Reflective-refractive material on the ground. Most likely, water droplets are the culprit here. The area (to me) appears to be the rough first pass of asphalt with some sand on it. Since there is no change in brightness from one material to the other, but the brightness in the center IS of the ground surface, it isn't a mist suspended in-air.

Quality of bright area diminshed with distance from the light source and/or increase of distance from viewpoint to center of ring along path of light in the direction of the shadow.
2. Diffraction around viewer (a focus mechanism?) plays a part in this. Additionally, this distance is crutial in getting the rainbow around the rim of the bright area, and directly relates to the angle between the viewer, the sun (assumed as the light source), and the spectrum.

Note that the ring is not quite circular, but that it is wider than it is tall. I'll admit I'm stsill trying to figure all of this out... I'm just thinking out loud right now...

scott.ellis@ps.ge.com

[Keegan]

So I've been enjoying exploring this and similar optical phenomena today, and have learned a great deal from you my cohorts out there, but I've been running into a brain-block. Emma gives an excellent description of how a rainbow comes to be seen, but logically to me at this point, rainbows must be viewed at a plane perpendicular to the viewer's line-of-sight (otherwise our 42 degree angles must get smaller, yet remain red...). In this case, the surface with the silica globes would have to be inclined at near 42 degrees in order to be perpendicular the the viewer's line-of-sight (42 deg. because of the elevation of the sun in Massachusetts--latitude 42N--on one June 20th--not because of the curiously coincidental angle of refraction/reflection of red through a drop of water also being 42 deg.). Our sand (or silica or other clear globe) doesn't seem to be sliding downward as if it were tilted at such an angle, so it seems a safe assumption that the ground is relativley flat.

Also, near the bottom of page 9 of this thread a link is given to a picture of a glass bead rainbow and described as having a 22.5 degree angle of return to the viewer's eye. If that were so, would our silica spheres also be a 22.5 degree angle? And would that affect any of our previous assumptions? My guess is 'probably not', but something is still bothering me about the summer solstice and the latitude of Mass. being the same as the angle of return that red makes through water droplets.....

Somebody set my mind at ease soon--by Dec. 7th I will have lost it!!

[tharrym]

Visible light is part of the electromagnetic spectrum that we see. Each color has a different wavelength. Violet is the shortest and red has the longest, that we can see. Light travels through space in a straight line until another force acts upon it such as dust or gas molecules universal gravitation..... The white light is visible when all the colors of the spectrum are present, as in the center of the halo. the violet light has the highter frequency and are absorbed more often than the lower reds. So violet light bends the most, which is why they are in the inner part of the halo and the reds are the are in the outersphere.
There are several ways to achieve this,especially if you are at a construction site. When light passes through different mediums it is refracted. It could be caused by dust or gas in the air or the ground, there could be glass or a mirror in the area to cause the light to change its speed and direction...........nano, nano

[Rusty]

The Prof took the picture with the sun above him, and it being June 20
the Summer Solstice, a phenomenon akin to a " sun dog" appeared.
The colors of the rings are arranged from high frequency, low wavelength
blue to lower frequency, higher wavelength red. It looks like it might
be on ice or maybe glass.

[Guest]

Also, near the bottom of page 9 of this thread a link is given to a picture of a glass bead rainbow and described as having a 22.5 degree angle of return to the viewer's eye

That's bystander--see above on this page

[ThinkAboutIt]

I think everyone is going to have to come to one of two conclusions

A)This is NOT a glory

or

B) the APOD editors lied about not knowing what this was

In fact, i would think that they probably used much of the same deduction you all have to guess that it was a glory, only to be told they are wrong, and thats why they linked to the Aug 6th APOD directly from this photo where it says explain the color

[Les Cowley]

The outer ring is a rainbow produced by small glass beads on the ground of the construction site. Glass spheres will produce a rainbow of about 22º radius which is the same as that of the image. A water drop rainbow is much larger with a radius of ~42º

The bright area inside the bow is normal for a rainbow and can be seen in the sky also.

The brighter area immediately around the shadow of the camera is a "heiligenschein" produced by backscattering form the beads.
More details on my site at
http://www.sundog.clara.co.uk/droplets/heilig.htm

[f12x@yahoo.com]

The rainbow is formed by light (from a source behind the photographer) incident on the surface shown in the photo. As the light rays enter the meduim (that isn't air), they are refracted a certain amount (blue is bent most, red least). This refraction is enough that the rays in the medium undergo total internal reflection when they arrive at another change in medium. The then are sent on a course towards the observer, and when they leave the medium they are refracted again. This would explain the rainbow halo centered on the camera's optical axis.

-Dan

[Guest]

I have read about some similar phenomenon to be seen from a mountain top somewhere in Germany. Has anyone else heard about that? I can't remember where I read it or what the explanation was.

[Guest]

Zounds, such complex explainations.

It looks like a "Camera Obscura" image to me. Somewhere behind and above the photographer is a opaque surface with a small opening in it. The photo is a picture of the sun projected through that opening. The spectrum is light bending as it crosses the edge of the opening.

Of course, I may not know what I'm talking about.

[Eburacum45]

I think that it is some spilled reflective paint with spherical glass balls, which appears to have been spread out on a flat surface by some kind of wheeled vehicle.
The photographer may well have noticed it while cycling.

Internal reflections have caused a rainbow effect at an angle of 22 degrees, as Les Cowley says.
inside the circle we are just getting white light reflected in a heilegenshein effect; the heilegenshein can be seen on the Moon in photos, as there are spherical balls of volcanic glass up there. Moondust also displays the opposition effect, where shaddows disappear, because it is loosely packed; I don't think that is responsible for the shine in this image, though.

[shoeguy101]

It appears to be sunlight near noon (June 20 !!!) passing through a leveling bubble on a tripod or transit for surveying.

[les]

http://www.clarinet.fi/~raimrask/Rainbows5.htm

[akiro]

this always happens at my grandma's house when the screen from the bathroom window is just about to fall off and the sun reflecting from Dad's 1966 Galaxie 500 bumper hits the bathroom window. Wham! same picture every time, now where do I collect my $20 ?

thanks, Akiro Kurosawa

[MC]

The ground is frozen from construction on the Boston subway causing ice crystals to be in the air near the surface. This allows the glory to occur.

[gabeef]

I think it is clearly heiligenschein or heiligenscheit. However, the spectrum around the edge is not usuall. Most of my experience with the phenomena is with the sun at my back and my shadow cast on wet grass. So, I wonder if the surface is important and perhaps the phase of the water.

[michael.edmonds@cox.net]

My guess at the setup in the photograph of this optical phenomenon would be:

The sun is very low near the horizon and at the photographer's back, so he’d be facing roughly east between 7:00PM and sunset on 6/20. It’s still damp perhaps following an afternoon rain. Sunlight is being diffracted through a circular opening behind him and projected on the wall in front of him. Perhaps there was a hole in a wall or structure at the construction site behind him projecting the diffracted sunlight on the wall in front of him where he saw the effect, stepped into the light path and snapped the photo.

Why? From the way his bag is hanging, I would guess he is standing upright, not bending over. If he was, he'd have set his bag on the ground so it didn't hang in front of the camera. Therefore, this should be a picture of optical phenomena on a wall of sorts and not on the ground and the axis of light is near horizontal. The wall and the image are warm colored so I would believe that this is close to either sunrise or sunset. Since the evening of 6/20 was the solstice, I would guess he was out snooping for pictures and looking for that Stonehenge kind of feeling between mysticism and science, perhaps. With the wet color of what appears to be a cement wall, I would guess its damp; maybe following an afternoon rain. Also, his shadow appears to be fairly bulky – still wearing rain gear or a shell, perhaps. The rings on the airy disc are nearly circular and broad spectrum, so I would guess the strong, white light source is directly behind him: probably the sun - given that’s often the subject of solstice seekers. Reflection, refraction or diffraction off-axis or through a rectangular piece of optics or grating would produce greater eccentricity in the circular rings. Circular lens are not commonplace on construction sites. Since there is no bright spot in the center of the shadow, I don’t think it’s a circular obstruction causing the effect. There is a big variance in light levels between his shadow, the light pattern and the rest of the wall. And, he has an “in the spotlight,” sharp shadow in front of this bright, airy disc. The scene would probably need far more consistent light exposure if it were to be a glory type diffraction effect. However, a diffraction pattern through circular opening could produce such an effect and the lighting variances in the photo.

[Greg Miller]

The horrible thing about a quiz like this is there are an infinte number of correct and equally likley answers based on the information we've been given. We simply don't know if certain aspects of the image were or if someone just walked up and snapped a picture and the whole thing is a natural phenomenon. The idea that the whole image is nothing but graffiti can't be discounted.

IMHO the shadow of the camera man can only be explained by one of these three explanations (all of which are equally likley based on what we know):

1. There are two camera men in a completley dark area. One taking a picture of the wall, the other taking a picture of the guy taking a picture of the wall. The guy in front uses a flash, the guy in back doesn't. The difraction pattern is caused by the non-normal surface of the wall.

2. The shadow is caused by the sun reflecting off of something. The diffraction pattern is caused by either what it's reflected off of, or somthing it passes through on the way to the wall. The camera man deliberatley stood in the center of the circle. No flash was used.

3. Same as #2, but the difraction pattern is caused by the wall and will "move" with the observer. No flash was used.

It's worth noting that the light area of the image is correctly exposed, the dark area outside the ring is underexposed, but the shadow of the camera man is directly in the center of the image which is where the camera would automatically measure the correct exposure. There are a dozen ways to correct for that, but it proves at least some creativity on the part of the camera man. And the problem with answering the question is how much of the situation is natural, and how much of it is man made?

[paladingroup]

Oil spill

[Steve Spicer]

There's a quantity of spherical transparent objects - or nearly spherical objects on the ground.

Your picture is taken with the camera lens at the middle of of image with the sun directly behind you (evidence shadow).

The sun is providing the light source - unless he got lucky with some other point source of light far behind him,

Transparent spherical objects are reflecting the light back at the light source, but there's also light being bent outwards and inwards.

Light from the sun is essentially paralel, so the illumination is even. However, when it hits the beads, light being bend inwards make the centre brighter (the colours get mixed up so we see white), at the edges, the light bent outwards make the familair rainbow order of colour - which I guess corresponds to the wavelengths.

You'd need to be on - or near on axis for this to be seen. Easy with sunlight.

[Chris Denesha]

What an awesome APOD!! I agree that this is excellent interaction, but I hope the APOD editors do not do this every day - I am spending 'too much' time on this as it is!

There were a lot of variables thrown out there on purpose, or else what good is a question like this? Please check out the links for 'students', 'colleagues', and 'APOD editors'. Obviously they are joking about not knowing the answer!

I agree with all who have said that it is a rainbow affect, which seems to be the same as a glory or heiligenschein (new words to me).

The site is a construction site, and the EXIF info (Noam Levy also thought to check this) shows that it is either 2:18 or 2:40 PM. I think the facts of it being the summer soltice at the 42nd latitude are there to throw us off. All that is needed is the proper surface that is perpendicular to the sun at that time of day...

The surface has many smooth particles for the sun to reflect off of. For some, the light is reflected into the particle, refracted twice, and then reflected out the particle in the direction of our eyes. For those particles at the right angle, we thus see the colors of the rainbow in the proper order. For other particles the light is reflected back at a small angle - the mixture of colors combine to make white light.

I once saw an excellent college physics explanation of all of this, and believe it was Professor Lewin!

chris