Lewin's Challenge Image

Comments and questions about the APOD on the main view screen.

APOD guess what it is

Post by Jack092251@aol » Tue Sep 21, 2004 12:18 am

I think it is a photo taken looking down from a bridge at frozen water.
the outer area is dark because the incidence od reflection is reached on the outer angles. The inner colored area is within the incidence of refraction for ice. There would have to be an even layer of ice above a layer of air or water.

Am I right?



Post by GT » Tue Sep 21, 2004 2:29 am




Post by mick » Tue Sep 21, 2004 4:18 am

I don't think it's that complex really.

if a flash was used why would the professors own shadow appear in the image?

i've seen this effect (or perhaps a similar one) several times before. It was caused by fine particles of glassy sand spread thinly over concrete or asphalt. The sun was high overhead and bright around noon. As you walk around the ring follows you. actually it's dizzying. i suppose it moves like when you're looking at a rainbow in a sprinkler and walking by.

maybe someone else has mentioned this (sorry). i just didn't have the gas to read the in-between 18 pages of posts.


Re: rainbow

Post by elija » Tue Sep 21, 2004 4:37 am

mick wrote:I don't think it's that complex really.

if a flash was used why would the professors own shadow appear in the image?
not a flash on the camera, a big light box (like the pros use). he's standing in front of it, and, therefore, casts a shadow. i shoulda been more specific, sorry.


Paul Morgan

Prof Lewin in the trench coat

Post by Paul Morgan » Tue Sep 21, 2004 4:51 am

Looks like pinhole camera effect, from a hole (a grommet, maybe?) in a sheet of canvas that was normal to the sun's rays on this longest day of Bean Town's year. The shadowy cameraman stood in the center of the limelight.



Post by MapleSD » Tue Sep 21, 2004 5:14 pm

camera aimed at window reflecting to ground, refraction from window and or window film.

otherwise...the glory idea was my original thought.

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


Post by Bob Peterson » Tue Sep 21, 2004 6:27 pm

The highest elevation in Massachusetts is found at the summit of Mt. Greylock at 3491 ft. Not very high for summertime freezing conditions, I would think.


time fluctuations

Post by spacermikey » Tue Sep 21, 2004 7:59 pm

when astronauts return from space, does their clock show an earlier time than on earth

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

More Beads

Post by Bob Peterson » Tue Sep 21, 2004 8:51 pm

Click Link. Look somewhat familiar? I have to stop obsessing about this matter and start obsessing about something else.

http://www.physics.umd.edu/lecdem/servi ... /n1-43.htm


Post by Brian » Tue Sep 21, 2004 11:38 pm

Earth - Bob
Come in BOB

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


Post by Bob Peterson » Wed Sep 22, 2004 1:20 am

Could be right Brian. Maybe I've been at the Space Station a tad too long. The best example supporting glass beads is a photo on the Japanese link furnished by ICE. I placed that link in one of my posts on page 19. For pavement markings requiring glass beads for retroreflectivity, there's a good chance for glass bead spillage. This is because the paint is administered first and then the glass beads are evenly spread on the paint surface. In the case of some small projects, the glass beads are spread on the wet paint by hand. If a machine is used, the paint and glass beads are placed in separate containers(another chance for spillage). If the glass beads are'nt embedded into the paint, but are laying free on the pavement surface, we have a whole new ball game with respect to light source and refraction.
Last edited by Bob Peterson on Fri Sep 24, 2004 3:18 pm, edited 3 times in total.

Col Man
Posts: 3
Joined: Wed Sep 22, 2004 3:35 am
Location: Leeds England

Post by Col Man » Wed Sep 22, 2004 3:45 am

is caused by the flash and the interaction of the light with the water droplets in the atmosphere.is a kind of rainbow effect...


Post by Mark » Wed Sep 22, 2004 9:08 pm

Did anyone else spot that it was summer solstice, putting the sun at around 70 degrees at noon in Massachusetts? Hence the shadow.

random dance

a p o d

Post by random dance » Wed Sep 22, 2004 10:12 pm

It looks like a photo of a slab of marble vibrating in the sun light eclipsed by the photografer


Post by ttt » Thu Sep 23, 2004 12:42 am

Photoshop works magic :D


Diffraction Corona

Post by Guest » Thu Sep 23, 2004 4:45 am

It can't be a glory as the colors are in the wrong order. Also most glories are
not as distict as his photo.

Otherwise, many of the same physical properties of a glory apply (bright
center region, shadow of obscuring object, etc.)

I do believe the powder on the ground is some sort of reflective medium
such as small glass beads or something like that.

The angle of incidence of the sun's rays on June 20 (summer solstice) in
mid-day would be very nearly 90-degrees even as far north as MA
resulting in a symmetrical display,

So I say it's a Diffraction Corona.

--Dave in Dallas

Diamond Dave

It’s a glassbow!

Post by Diamond Dave » Thu Sep 23, 2004 3:16 pm

It’s a glassbow, created by dispersion by artificial spherical glass beads. The artificial glass beads are likely derived from the leftover ingredients used to make reflective white lines on roads. The arc is brighter on the inside then the outside, like a typical rainbow but unlike a fog bow or glory. The light is split into a spectrum by dispersion not diffraction.

The angle of the bow is not as large as a rainbow. That's why it looks odd, the photo has properties of both rainbow and glory, thus the confusion. This is a very important point. Water has a much lower refractive index then glass, 1.33 V’s 1.55. Thus a bow made by glass beads will be narrower then one made by water droplets. Light is bent at a more acute angle in glassbows.

Fog bows and glories produce even narrower arcs, by diffraction. The particle size has to be minute and the same size. Sand does not form such small particles, it is soluble it is micron sizes and is never uniform. Glass beads cannot be made in uniform micron sized grains by the billions, unless you go into space – zero G helps.

If it is dispersion, the grains are perfectly spherical and glassy smooth. Sand is rarely round unless windblown. Windblown sands maybe spherical but grain surfaces are pitted and scarred by impacts with other grains making grain surfaces matt.

No, the material consists of tiny man made glass beads, the left overs from road marking. It’s not surprising that the phenomenon was photographed on new looking tarmac road.

Atb, Diamond Dave


Re: Lewin's Challenge Image

Post by Eddie » Thu Sep 23, 2004 5:28 pm

It appears the Doctor is taking a flash picture of the dust covered ground at a construction site. This is his shadow in the picture. The flash caused the bright central light, which has been blocked by his body. The dust on the ground has been disturbed and diffracted by the flash, causing the halo (moondog or sundog) effect.


Post by eddie2 » Thu Sep 23, 2004 5:40 pm

The Doctor is taking a picture of a dust covered floor at a construction site but is not using a flash. The overhead sun has cast his shadow in the picture and has caused the bright central light. The dust on the floor has been slightly disturbed and diffracted by the sunlight, causing the halo (moondog or sundog) effect.



Post by Kathy » Sat Sep 25, 2004 2:38 am

Nice picture. I have a guess. You are standing with the sun behind you, obviously, the sun shining onto a slab of polished stone and reflecting back through a pane of fogged up glass or sheet of plastic, the water droplets refracting the sunlight into an inverted circular rainbow right before your eyes? That would be a very "cool" thing to see.
Kathy A. Collins


Identify this phenomenum

Post by Jack » Mon Sep 27, 2004 6:06 am

My gues is the "rainbow" pattern around Prof. lewin's shadow is produced by tiny ice crystals high in the atmosphere. I believe I read somewhere that mountain climbers have seen similar effects.


Prof Lewin's Image

Post by jupton » Wed Sep 29, 2004 2:06 am


It's direct sunlight reflecting/refracting through the viewfinder of the camera causing the prism and circular effect being projected onto the surface.

That and a dollar will buy you a soda.

Jackl Upton


Prof Lewin's Image

Post by jupton » Wed Sep 29, 2004 2:14 am


It's glare from the white road surface reflecting back onto the camera lens glass causing the circular and prism refraction.

That and another dollar will buy you another soda!

Jack Upton,

User avatar
Posts: 12
Joined: Wed Sep 29, 2004 7:28 pm
Location: Seattle, WA, USA

Post by wbeaty » Wed Sep 29, 2004 7:51 pm


With a bag of beads, you can reproduce Dr. Lewin's photo at any time. A sunny day is required though.

I still have about 100LBS of the stuff out in my garage; bought for distribution at the monthly meeting of the Seattle Weird Science Salon. We also used it in 1992 for a science museum exhibit on rainbows. And this June I put rainbows on the sidwalk at Seattle's COCA gallery. Guerilla physics-art!

(((((((((((((((((((( ( ( (O) ) ) ))))))))))))))))))))
William J. Beaty billb@amasci.com
Chemistry Dept. #74 Bagley Hall
University of Washington 206-543-6195

User avatar
Posts: 12
Joined: Wed Sep 29, 2004 7:28 pm
Location: Seattle, WA, USA

Post by wbeaty » Wed Sep 29, 2004 7:54 pm

The "underground sidewalk-rainbows" effect also works great at night under a single streetlight.

When I develop enough ambition, I go and sprinkle a bit of the stuff on the sidewalk surrounding the bronze Jimi Hendrix statue on Seattle's Broadway Avenue:
http://www.vrseattle.com/html/vrview.ph ... _id=vrs756

(((((((((((((((((((( ( ( (O) ) ) ))))))))))))))))))))
William J. Beaty billb@amasci.com
Chemistry Dept. #74 Bagley Hall
University of Washington 206-543-6195