Starship Asterisk*

That camera guess was mine btw, forgot my name.

The professor does wear glasses too http://mit.edu/8.03/www/ maybe that has something to do with it?

Was anything set up, or was this photo possible because of the setting or because of conditions already present at the construction sight?

I spent 17 years at 3M working on retroreflective sheeting and traffic markings. Most of the information on retroreflective optics is found in patents. Search google or the us patent office for retroreflective bead optics. also see http://www.pottersbeads.com

Wouldn't total internal reflection would cause a true rainbow circle? I think the conditions are met only for a narrow range of angles.

I think that the light is reflecting specularly off the rear curved glass-air interface of the bead and tends to be redirected to its source by the curved front glass-air interface. This leads to a fairly uniform intensity distribution within the ãpprox. 25 degree cone of light that is observed. The cutoff angle depends on the refractive index and ( i think) the bead diameter.

This phenomenon is very similar to the Glory with Brocken Specter. However, the Glory naturally occurs due to water droplets. In a Glory, the angle of the rainbow effect is much larger with respect to the bright inner region. In this phenomenon, the angle of the rainbow is much narrower in relationship to the inner bright region. For this to occur, the spherical medium reflecting and refracting the light would need to have a radius different than a water droplet, so the reflecting angle of all the colors (the white portion) would be larger than the refracting angle. Likely, the material is those glass beads (used for spraying on top of fresh roadway markings to make the marking reflective), which has been spilled on the pavement.

I'm tempted to write a computer program to simulate this effect (if I can find the time). It would be interesting to adjust the radius of the spheres to see how the angle of the rainbow is affected. If I do, I'll post the results.

It looks like an ordinary rainbow to me.

The photographer is standing close to a dirty window with the sun directly behind. Behind the glass is a spray of water. Maybe a spray to keep setting concrete cool?

The brightness in the center is the normal rainbow effect where light rays within the rainbow angle are reflected back to the viewer and those outside are not.

Perhaps the glass is at an angle and the sun is fairly high in the sky and the photographer is bending over slightly. If the glass were vertical, the sun would be near the horizon and the rainbow might not be so bright.

There may also be a very slight "halo" around the photographer's head due to the fact that the dust particles in line with the sun are covering their own shadows while those at a greater angle are not.

It is Sunday june 20 and the professor is standing directly under a crane in a construction site. (likely one of those big biotech buildings going up.)

When the crew left on Friday they hoisted a heavy pipe with the crane so it would not blow around.

The pipe, maybe, a foot in diameter is 60 feet up and is dangling at an angle of 22.5 degrees from vertical.

The shot is at high noon when the sun is 22.5 degrees from vertical.

The effect is simple constructive and destructive interference of the light from the sun's disk passing through the pipe.

Like shooting a laser through a slit but using all the available visible wavelengths. Does that make it a fresnel fringe. It's been a while.

Either that or it is the crane ball alone way up there and a more difficult to explain interference pattern is going on.

It's a simple rainbow, except that instead of raindrops, the light is bouncing around in glass spheres embedded in a concrete wall (or floor?). These spheres are added to the mix to give a concrete with a lower density and higher strength-to-weight ratio. Since the spheres are throughout the bulk of the concrete, a significant number are exposed on the surface. The optical properties are just a bonus.
One source of these spheres is http://www.bluecirclesoutherncement.com ... efits.html, but googling on (concrete glass spheres) will find many other links.

Got a reply to my email. (sent 24 hrs ago) Correct enought for an extra course credit!

My favorite examples of the glory are in pictures from the moon. Look for the shadow of the astronaut's head in these examples:

Astronaut Glory Pictures
http://www.apolloarchive.com/apollo_gallery.html

http://www.hq.nasa.gov/office/pao/Histo ... 0-5882.jpg

(I know that there are many answers like this one, but I don't speak English enough to write mine quickly, it took me a day to write it. Be patient, my English is a little poor...)
First of all, I think it's obvious that the light can not be produced by a flash, simply because of the shadow of the man: to produce a shadow like this one, the source of light (the flash) must be behind the man, not in his hands!
My first thought was the Heilingeschein, but this phenomena usually fades "slowly", doesn't have the color border shown in the picture. Maybe there is a little of this effect, but just in the centre, around the shadow of Lewin's head. So, I think it's a rainbow; 1) the brighter area inside; 2) the colorful border and the dispoSition of the colors (red on the outside, and blue and violet on the inside), and 3) the darkness outside, these three effects are typical of the rainbow.
It may be caused by a high density of little drops of water between the source of light and the ground, or something that acts in a similar way, maybe with a different angle of refraction. If it's water, it could be artificially produced by a machine in the construction area (i don't think it's natural fog because the shadow has sharp edges, not like in a foggy day). I tried to make this effect yesterday at 13:30 in the south balcony of my house, in Girona (Europe), with a spray of water (the kind you use to vaporize plants or to iron clothes). I stayed with the sun behind me, and vaporized in front of me. The result is a round rainbow around my shadow, not an arc but a complete circle, just interrupted by the shadow of my own legs. Yesterday, in Girona, at 42ºN (just like Boston, Massachussets), at 13:30 (local time), this circular rainbow was "floating" in the low front of me. If I wanted it on the ground (just like the picture of Lewin), I think I should wait until summer equinox, when the sun is higher, and even bend myself a little, like doing a reverence.
There is a second possibility: the rainbow is not produced by waterdorps, but by another spherical medium (don't know which one). This would explain the size of the circle, that appears smaller than the one I made at home, maybe because of a different angle of diffraction.

Montse Bosch

Glory & opposition effect, isn't it?

Hi

I posted my thoughts on this earlier. These can be found on page 5. I have been in contact with Prof. Lewin and this solution is correct and the grains of material on the ground which he used to produce the effect is bow glass

Emma

http://www.sundog.clara.co.uk/droplets/globrock.htm
http://www.sundog.clara.co.uk/droplets/glory.htm
http://www.sundog.clara.co.uk/droplets/heilig.htm

It looks like a glory and Heiligenschein to me. The white powder is acting like the waterdroplets in a glory. The links I put above show a glory but the spectrum is more dispersed. I think that because the poweder particles are more uniform in size and the distance from the observer and powder is a plane the spectrun is "finer'.

Hello,
Can anyone tell me what is "bow glass"? I suppose it can be "fibra de vidrio" in Spanish, used for example for making boats, but I'm not sure.
Thanks.

Emma wrote:Hi

I posted my thoughts on this earlier. These can be found on page 5. I have been in contact with Prof. Lewin and this solution is correct and the grains of material on the ground which he used to produce the effect is bow glass

Emma

Check out this "road paint bow" - look familiar?

http://www.geocities.com/bowlturner/unu ... inbow.html

The true "Broken spectre with glory" phenomenon requires misty atmospheric conditions in line with and distal to the sun-viewer axis. Judging by the crispness of the author's shadow here, I assume bright, summer equinox sunlight in clear air. Therefore, some substance on or very near to the ground is likely to be responsible for the disc reflexion and annular diffraction. Could it possibly be that the author has wandered into line with a shadow cast from a higher structure (e.g. crane jib) and has imaged it's "glory" around his own standard shadow?

Dear, oh dear - that should of course be "reflection". My appologies.[/i]

It's a normal simple rainbow. The lighter area inside the circle, and the blue on the inside of the circle and red on the outside confirm it. The water droplets are between the camera and the darker background scene, probable from a lawn or flower mister. You could do the same thing with a lawn sprinkler.

Just your basic Pilots Halo. I see it almost daily from the cockpit.

Its a white light shone directly at somebody taking a picture of the light on a misty night with the professor taking a photo directly behind them with his flash turned off

It looks like a flash lite with an adjustable lens to me!! Maybe some mountain climbers haveing fun. They shinned the light on the snowy granit wall held up the camera and someone from behind snaped a picture. Like the painter painting a picture of the painter.

All,
Prof Lewin sets the APOD world a puzzle, announces that he will reveal the true explanation in December and sets the bulletin board ablaze.

Meanwhile, he spills his explanation to "Emma", who tattles here. What a disappointment! That either he cannot keep his word or that he has friends that do not honour his confidences.

Prof Lewin, learn better manners or get better friends.

John

Nice photo of a "glory"

Also note the bright spot in the center or the image which is partially shadowed by the photographer. It is a pile of the glass beads which has been swept together to create this image. Secondly note the versatile talent in the APOD readership.