Starship Asterisk*

My quick explanation of the photo is that this is a picture taken of reflective beads (spherical beads as used to add reflectivity to highway signs or roadways). The sun, of course, is directly behind the photographer. The particular zone of reflection is due to the spherical nature of the beads. The phenomenon also occurs when you look at dew on the ground with the sun at your back (heiligenschein) or from an airplane look at clouds below the airplane (glory).
The substance on ground (pavement) might also be very high silicate sand - very fine grade.

My vote is for Spectre of the Brocken: http://www.sundog.clara.co.uk/droplets/globrock.htm

It means there had to be water droplets in the air, but as someone speculated, maybe there was water sprayed for dust control.

I'm afraid I'm not convinced by any guess made yet.
The main problem here seems to be the dark area outside the "glory" which BTW I don't believe has that much to do with the picture...

Wondering why all the people here seemed to believe the camera was pointing the ground instead of a wall...

Two more questions:

1) is this a picture of something Prof Lewin SAW that morning (placing THEN himself straight in the center...) or taking the picture itself CAUSED that?

2) obviously the light source is behind Prof Lewin and this explains in some way the light concentration, but is there something between the camera and what I believe it's a simple wall?

I do apologize for my bad English, ciao

Stefano

It's a glory for sure, but we don't get enough information about the environment to say what causes the phenomenon. Water vapour as some have suggested is possible, but it could also be very fine dust grains, either in the air or on the ground. In that case, the spectrum is caused by dispersion rather than refraction.

The EXIF information is still intact so there is no need to speculate about the time and date of the picture; a lot more useful information is available from this:

The picture was taken on June 20 at exactly 14:40, camera used was a Canon EOS digital rebel.

ISO100, 1/2000 second exposure at F/5.6. This is an extremely short exposure time, meaning the object was very bright.

What if the source of this light is not a flashlight, but a high powered construction lightbulb?

It is a 'glory'.

i suppose the picture shows the "heiligenscheineffekt" called in german. heiligenschein is "holy light in english, the bright rings above heads of angels.

my explanation:
very small water or ice particles on the floor refract light of the sun, so that the area around the observers shadow is brightened up.
i suppose, the coloured spectre ring around this bright zone on the floor is caused by refraction on particular sizes of ice crystals or waterdrops on the floor. and only the person, who causes the shadow can observe the phenomenon.

another pic of this phenomenon:


i hope you did understand my bad english

some pics like this (other atmospheric phenomenons) on my website:
http://www.kopfgeist.com/fotos.htm

greets

jens

refractive effect on surface with tiny crystalls ?:))

It looks like a Brocken Spectre. The Brocken Spectre appears when a low sun is behind the climber who is looking down from a ridge or peak into mist. The glow and rings are of course a glory centered directly opposite the sun at the antisolar point. But what then is the ghostly figure? It is no more than the shadow of the climber projected forward through the mist. All shadows converge towards the antisolar point where the glory also shines. The sometimes odd triangular shape is a perspective effect. The Brocken Spectre is a similar effect to anti-crepuscular rays and cloud shadows.

It appears to be the diffraction of the light of the flash of the camera by the construccion area, which is acting like a prism, and as the light of the flash bounces away, so does the ring(rainbow).

It is the flash of the camera reflecting off a type of Crystal Quartz in the rock.

I am not even a college graduate but hope I can offer a simple explanation... The caption mentions that the photograph was taken on a worksite. There's silicone all over the ground.
The silicone acts much in the same way the clouds do when looking towards the shadow of the aircraft you may be flying on.
If my memory serves me correctly it's called the 'Angel effect' and can also occur when looking down one's own shadow from a mountaintop.
If any of what i am saying is correct, i'd also be prepared to put a small wager on the rainbow 'halo' being the same angle from the camera lense, as the sun has to be in the sky to cause a rainbow.??? Which i think is around 45 degrees.
Please correct me if i am wrong.

While some might think that Prof. Walter Lewin is angling for canonization or using his body and camera to create a pretty good shadow of an Apollo LEM on the moon's surface, my explanation is that he took a flash photo of a wet surface, and the flash and the wetness created an effect of the halo.

Ok the caption states...
Your answer should be able to explain the color sequence and the bright area in the center.

That is the SUN causing the shadow. Not a camera flash or anything like that.
Obviously Infa Red is on the outside of the ring. This is consitant with a rainbow caused by water - this halo is caused by sand i am sure as it looks like sand to me. Infa Red is refracted the MOST, and Ultra Violet gets refracted the LEAST - (this is also a guess as i look at my bedroom lightbulb in the reflection of a Compact Disc.)

The bright area in the centre is caused by the silica reflecting ONLY that light which is within the (45 degrees i think) of the halo. The silica obvoisly doesn't refract light more than that point. - This explains why the outside of the ring being dark.

I thank you.
Jeremy - Sydney - Australia
...
..
.

Hi

I think that I can explain the photo

This is a the same as the physics occuring when a rainbow is formed. The ground must have had some kind of grains in it that were spherical in shape which light can pass through.

Consider just the top of the rainbow pattern. The light refracts once upon entering the grain and the blue light is refracted through a greater angle than the red light as it has a larger index of refraction. The seperated light then reflects of the back of grain and the blue light is therefore deflected upwards more than the red. The light is the refracted again upon leaving the grain causing an even greater seperation. Because the blue light is upward more, the blue light which reaches the camera comes from grains which are lower down. This happens the entire way around in a circle and explains the colour ordering.

The bright area in the center is also a phenomenon which can be seen in rainbows (there is bright section either side of the primary and secondary rainbow with a dark patch in the center). The light paths for parallel rays through the grain which produce the rainbow pattern come from the grains that are furthest from the center of the circle which have single reflections. All others reach the eye from further in grain which lighten the area. This effect is made even more noticable because any grains further out than the circle can not bend the light towards the camera which makes this region darker than the actual ground.

There should be a 2nd circular rainbow further out on than the photo with the reverse colour order which corresponds to light which is doubly reflected within the grain. Further out from here would be another light patch.

A good website which explains rainbow physics is

http://hyperphysics.phy-astr.gsu.edu/hb ... on.html#c1

That's exactly how i tried to explain it.. except my compact disc has taught me differently.
Thanks!

Emma, you have convinced me to go to University as a mature age student!
I loved your explanation!
It exaclty how i wish i could have written what i can see in the picture.
Brilliant. Thank you.

The rainbow which you see when looking at your compact disk is formed by the circular tracks around the disk acting as a diffraction grating. This is a similar concept but not quite the same.

Even still it was a pretty good guess. I'm actually a third year physics student at university and optics is taught at from 1st year onwards

The image is a projection of the sun on the ground through a small hole, probably a sheet of heavy steel. The construction workers most likely set it up to watch the transit of Venus. The two color rings are likely caused by the corona of the sun and earth's atmosphere.

Yes it is a very different process.
I'm not looking for a reply but I am disappointed then that the UV end of the compact disc spectrum appears closest to the lightbulb in the disc?
Never mind. My hypothesis was a stab in the dark.
I absoultely agree with your explanation and found the link you provided to be a perfect example of what we/ you wanted to say.
I didn't think any of the other answers to be anywhere near close.

Tell me you're Joking Sy Kaplan!!
PLEASE!

Sy's answer is incorrect. Although you would see a ring pattern it would be quite different. You would get what is called a Airy Disk pattern which is a circular pattern of bright and dark regions.

My solution is actually correct and I have emailed Walter Lewin (the photographer and physics lecturer at MIT) who confirmed this.

Silica sand from a sand-blaster produces the halo effect from reflection and difraction.

It appears to be a form of Glory, or Brocken Spectre. I assume the sun is in back of the photographer and there is frost or dew on a dark smooth wall in front of the photographer.

Bob LaMontagne
Providence College