Starship Asterisk*

I think that the professor is photographing a thin layer of oil.

I think that the rainbow forms by the same way. More clearly is explained on the draw: (In order to be more clear, I painted only the voilet and the red rays)

Although I am not sure what is causing the colors (oil, refracting elements in the payment??), isn't this a combination of a "glory" and a "Heiligenschein?" (See APOD 8/6/2004)

The image seems to be the projection of a light source thru a big convex lens, before the focal lenght.

The fearless physicist gets in the path of the light and snaps the photo.

Keep APOD alive !! - I enjoy it every day
Miguel - Mexico City

At first I thought this was an example of a heiligenschein counterglow, perhaps off fine oil droplets, but the well-defined outer colored ring and bright inner area is exactly as a rainbow would appear, only in this case we are seeing almost the complete bow. It's not clear what the angle of view of the lens is but it could be wide enough to take in the 42 degree radius of a bow -- an ultrawide lens would make the bow appear smaller than it really is, plus the fact it is projected onto a nearby surface not on the distant sky (a reverse moon illusion). So my guess-- a rainbow, with droplets of water on the pavement as the source, or could it be a bow from droplets of another liquid like oil??

-- Alan Dyer

OK, here goes. I think the surface is a wall, the photographer is upright, the sun is directly to the east and the photog. is facing west, and the effect is a nearly full rainbow (missing only the photog's shadow) with the scattered light scattering toward the inside of the bow and away from the outside of the bow, as rainbows do. (I think this rules out the glory.)

I think the ultimate cause is a (remarkably uniform) early morning dew on an east-facing wall on the solstice, when the sun hits such a wall at exactly a right angle. The wall looks nearly-but-not-quite smooth to me, such as new but cured concrete, and the porous surface has provided a lot of close-packed sites for dew formation.

The photog is not doing anything unusual to get the shot, just standing a few feet away, with his(?) back to the newly-risen sun, taking a normal picture with any film that shows color well and perhaps just a little adjusting of aperture, exposure time, etc. to emphasize (but not create) the effect. In fact, I suspect that the photog did not have time to do much more, as it looks more like an unplanned, serendipitous event, in which case he(?) would not have much time before the sun rose too high and the effect disappeared.

I realize that most of this has been posted to this discussion by others, but perhaps not this exact combination of factors spelled out this way.

Thanks. It's been fun.

I believe this phenomenon is similar to what sailors call "moon dogs" or
"sun dogs". As most physics buffs realise, all rainbows are actually rain circles in which moisture acts as a prismatic lens breaking up white light into it's component spectrum. The light behind the man on the cell phone is probably the sun or a very bright arc lamp. (high pressure sodium?)

Upon further reflection, if you will forgive the pun, I have come to the conclusion that this is solely due to the point of observation, there were no additional devices utilized in creating the picture, and it is naturally occurring.

Imagine if you will the multiple rays of light coming from the sun. The rays are parallel, for all intents and purposes. This will create an even lighting of the ground in all areas that are flat. (Reference all areas outside of the "rainbow" - for lack of a better word.)

No light comes from the area of the shadow, for obvious reasons - it is being blocked by the photographer.

The bright area is reflection from the particles on the ground (water droplets?), and the brightness is evenly distributed within the circle. When we get to the edge of the droplets' ability to reflect the light, we get the bending of each color component in the order of most easily bent (violet) on the inside to least easily bent (red) on the outside. This is representative of the parallel light beams from the sun reflecting on the backside of the droplets in it's dispersion of the spectrum. Outside of the red ring lies beyone the angle in which the sunlight will do anything more than light the surface.

I don't believe that the picture being taken near the solstice or at a particular latitude has much to do with it since the area over which the illusion appears seems to be about 4 feet across, judging by the size of the shadow. In other words, the conditions aren't that much different than on any other day.

scott.ellis@ps.ge.com

Reference my above posting:

I mean internal reflection of the water particles in creating the bright area internal to the "rainbow", and in the creating of the "rainbow".

scott.ellis@ps.ge.com

A greasy wet floor during high noon.

[quote="ahecht"]The actual effect, I assume, is very similar to the one in this old APOD: [url]http://antwrp.gsfc.nasa.gov/apod/ap040806.html[/url][/quote]

But why are the colors inverted if that is what is happening?


Nicole

Ok I have read "ALL" the links, some really bizzare stuff out there. Anyway.The only thing that makes sense is the fine little glass beads on on the ground, probably a bag of them got spilled. There are obvious scuff marks or tracks through the stuff. At the the 2o'clock position the halo is almost gone and the surface is much darker. ie No Beads. Why is it brightest dead center. The sunlight reflecting straight back from the beads. The halo is a "glory". Way is it not an ellipse. Because the camera is a the focal point "center" of the halo. And last I checked, the water droplets that form rainbows are not at exactly on the same plane either. Looking at the shadow I would guess the sun to be at about 50 to 60 degress. And no I don't think he is wearing a heavy coat, just a shoulder bag full of stuff (camera supplies?). Yes, I have a hard time thinking there is any ice on the ground in massachusetts in June during the daytime.

I am a bit late, but I think this is essentially a 'Glory' as we've seen on APOD before.

I think that the ground is covered by the reflective beads that they use on road markings such as crosswalks.

My guess would be that FiberMesh, which is sometimes used in concrete, is reflecting light of different wavelengths (hence the rainbow appearence and bright light in the center) from the sun and the flash of the camera. FiberMesh is ground up fiberglass mixed up in concrete to strengthen it and to keep it from pulling apart if it cracks. The photographer is taking a picture of the ground with the sun behind him, so we see his shadow. Just a guess.

One thing I forgot to mention. If Prof Walter Lewin is like most professors he is not going to spend a lot of time staging a photograph. He might ask one of the construction workers to dump some glass beads on the ground, (paying the guy would be unthinkable). I think he was probobly walking to his office and noticed the halo, whipped out his trusty camera that he keeps with him in case he is around for a plane wreck or a bolide or what ever, one never know, and he took the picture. APOD July 28, 2001 or APOD Oct 1, 2003.

Dear Professor

Like myself, you suffer from male pattern baldness. And, if like me, your remaining scalp is smooth and shiny, it can bend light like no other phenomena in the universe. Just be careful, with just the right tilt of the head we can blind someone on a sunny day.

Best of luck with the other "guesses."

A ball of water in orbit?

perhaps colors formed by some reflection and despersion of light in a moisten place after it rained or there was fog.

I can see two options.

The first is a tiny hole in a roof/wall far above/behind is projecting the sun (like a pinhole camera) onto the photographer's back, with the light of the sun diffracting a little around the edge of the hole. If the hole is round this would work...not quite as predictable if the "pinhole" were irregular. (science freak answer)

The second is an ellipsoidal spotlight in tight focus lighting the photographer from behind. The ellipsoidal reflector keeps the light which hits it in tight "mathematical" focus, but the light which goes straight through the lens without hitting the reflector is mostly blocked by a black circular gate placed at the focal point. Some light makes past the gate and through the lens, refracting a little as it went past the gate, making the rainbow effect which is stretched out by the lens. (showbiz guy answer)

From what I've seen; Glories, or Brocken spectra, or angels appear as multiple concentric colour rings, with at least one dominant red inner ring, surrounded by a green and blue ring.

This is quite clearly a bright white central reflection with a single rainbow around it (blue on the inside, surrounded by green and red).

Rainbows are caused by reflection inside raindrops, the angular radius of the arc being independent of the size of the raindrops, whereas Glories are diffraction effects, with the radius dependent on the size of the (much smaller) mist or fog particles.

In this case, the effect seems most likely to be caused by glass microbeads, normally used to give a high reflection surface to signs but here they have been spilled on the ground.

As the photographer stands with the sun behind him or her, the beads give high reflection back towards the source (behind the photographer's head), and a rainbow effect further out.

A fascinating image and excellent to have an 'interacive' APOD.

sirs:

the image is of a photographer's shadow in front of the light phenomena.

seems to me that the light source in the photo is from the "shadow photographer's" camera, i.e., if the light source were behind him, he would not be a "shadow," he would be illuminated.

it is likely the "shadow photographer" is right handed, statistically speaking, and that would be consistent with the image in the photo, assuming another person taking the photo from behind him.

i have read all of the submissions, and like emma's the best (other than my own, of course), but i have yet to read anything which would explain how the defracted light is focused in concentric rings around the circumference of the illuminated circle. now, i can imagine beads and the like defracting the light, but how does it focus it?

the only way i can imagine light being focused in such a manner would be if it were not in fact on a flat surface, but were some sort of spherical phenomena is a very dense fog, or water mist, as some have suggested, but i still don't understand how it would so sharp on the edges of the circle.

if the light isn't split somehow and focused onto a surface, is there anything which would explain how it might have been projected from the camera flash?

obviously, i cannot get over the issue of how the defracted light is focused to the edge of the image so finely.

emma, do you have any explanation?

john jay

It looks like an oil splatter on the ground with the sun shining down on it. The oil droplets, perhaps mixed with water droplets act like a prism creating a rainbow effect. You cannot see the sun because the photographer is blocking its view.

jojojay@charter.net wrote: i have read all of the submissions, and like emma's the best (other than my own, of course), but i have yet to read anything which would explain how the defracted light is focused in concentric rings around the circumference of the illuminated circle. now, i can imagine beads and the like defracting the light, but how does it focus it?

John Jay
The different colours in the sunlight are thrown off at the same angle from all of the beads, but only around the edge of the bright area does the light come into the camera. It is exactly the same as the reason a rainbow has such a distinct shape.

see the second rainbow diagram on this webpage
http://physics.uwstout.edu/WX/Notes/ch15notes.htm

http://antwrp.gsfc.nasa.gov/apod/ap040806.html

A Link to August 6....surprising that no one caught this. It seems to be the same phenomenon as the Sept 13 image. Challenge...PAH!

If I could take a guess, I would have to say it is the "Opposition effect". The soil being very open in this case could, around the anti-solar point, hide the very shadows it creates. This would account for the bright centre of the object. This is to say, more sunlit surface as compared to shadowed surface. Heiligenschein to my knowledge is caused by water droplets.
My guess then would be a combination of the two effects.