Lewin's Challenge Image

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

Lewin's challenge

Post by guest » Mon Sep 13, 2004 2:39 pm

This ring of colors and the bright center is created similarly to a rainbow. The observer is facing directly opposite the sun. The bright center is caused by the light from the sun being reflected at smaller angles than the outside ring and since all wavelengths are reflected it appears white. The dark outside is due to most all of the light being refracted at smaller angles and very little if any being refracted at larger angles therefore little light is seen outside the ring. The colors are explained by Descartes when he did his experiment and discovered that at an observation angle or approximately 42 degrees you see red light and when the angle is decreased the other colors become visible.

guest

challange picture

Post by guest » Mon Sep 13, 2004 2:45 pm

I have been coming to APOD for years now and wouldn't miss a photo, ever! This subject has been touched on before: http://antwrp.gsfc.nasa.gov/apod/ap040806.html

It is commonly known as "the glory".

Thanks for providing an intelligent discussion on the web.

Jason Humphrey
Denver, CO

Peter Thomas

Aperture Bebunked

Post by Peter Thomas » Mon Sep 13, 2004 2:57 pm

The shadow extending ouside the circle does not debunk the aperture theory. It is a construction site and there would be some ambient light from dust scattering light. Still, I don't think it is a light shaft anymore. It's two perfect of a circle, the aperture would have to be perfectly circular and perpendicular to the light shaft.

I am now inclined to believe it is a point source light, like a construction light in a tunnel (Big Dig in Boston). The effect is similar to a glory, but two dimensional not three dimensional. There is something on the wall like dew, sand or maybe beads from blasting the surface clean. With a glory, the relective/refractive material, water droplets, is spread in three dimensions, not limited to a two dimensional coating on the wall.

Here's what I think is happening. It is a combined effect of relective surface and the camera lens. Dew or beads are bouncing light back in the direction of the light source but not directly back, spread in a cone refracted into a cone. Red at the edges of the cone and blue in the center. The camera has a large aperature and inside the circle the lens is reintegrating the refracted light so it appears to be white.

If a longer exposure with small aperature, the entire circle would appear white.

Meeker77

Lewin's Challenge

Post by Meeker77 » Mon Sep 13, 2004 2:57 pm

I'm going to go with it's a "glory" and that it was taken in the morning (phtographer's jacket outline) and it was a heavy dew on the ground or depending on the construction site it could have been very small pieces of glass or quartz-like substance (ie very fine sand, possible from plasting) or a combination of both.

Check this site out, for some of you who think it can't possibly be a glory for it's too close to the photographer:
http://www.weather-photography.com/Phot ... igenschein

Purdue ME student

Not Diffraction - But maybe an inclined surface

Post by Purdue ME student » Mon Sep 13, 2004 3:01 pm

I cannot agree with the aperture thory, because not only would this significantly diminish the photographer's shadow, as previously mentioned, but one of the most important things I learned in physics about diffraction was that it must be monochromatic light in order for diffraction to have an effect. Also, for the wrecking ball theorists, if the ball is so far away that it can be covered by the photographer's head, then the effect of diffraction around the ball would be even less noticeable.
As for the fact that the circle would be an ellipse if it was on the ground, it is possible that there was an inclined surface that was perpendicular to a line between the observer and the sun. This was a construction site, so there would be sheets of paterial propped up and waiting for use.

Emma's theory makes the most sense to me.

Contractor

Lewin's rigged photo

Post by Contractor » Mon Sep 13, 2004 3:02 pm

First of all the background is a stabilized base pavement. It had obviously been swept free of this unknown particulite more than likely a dust control or a light snow dusting. When Lewin realized he could have it swept closer to bare pavement, he had it done. There are wheel marks indicating some sort of mechanism was turning. He left if heavier in some spots closer to the shadow, and infringed on the circle at about eight o'clock. Rather than lose his shot he neglected some areas outside the ring. I assume the halo is some sort of glory phenomenon that responders are talking about, but how would I know? I'm just a contractor. (Retired at that).

sterling o

brain teaser

Post by sterling o » Mon Sep 13, 2004 3:06 pm

First off, it's great that APOD has decided on a little interactive brain teasing from its dedicated viewers. My first thought was of course, the glory phenomenon, but if this is correct, how could it be that the APOD editors would not have identified it. So I'm stumped. My next lead may be the date it was taken. June 20 is right around the summer solstice... Could this be some sort of event occurring on or near solstice days? As for the construction materials, I don't know much about that, but its as good a guess as anything else. Thanks for guess work, I'll be eagerly anticipating the correct answer...

Trudy E. Bell, Science Wr

APOD 9/12/04 - construction rainbow

Post by Trudy E. Bell, Science Wr » Mon Sep 13, 2004 3:06 pm

I am virtually certain it's the full circle of the rainbow, likely reflected from traffic beads, as I photographed myself a couple of years ago here in Ohio.
I'm willing to wager it is NOT the diffraction effect of the Brocken specter or the glory - those are often produced by microscopic fog-sized particles close to the wavelength of light, whereas traffic beads (like raindrops) are much larger than the wavelength of light. How can I tell? The outer ring is red, and according to Greenler all phenomena produced by refraction have the red edge toward the sun, whereas phenomena produced by diffraction have a blue edge toward the sun.
The bright area inside results from the fact that in a rainbow, more light is scattered inward (toward the antisolar point) than outward. There may also be some kind of heiligenschein effect contributing to the interior brightness, especially around the photographer's head. - Trudy E. Bell, Science Writer

J.David F.

Professor Lewin's picture

Post by J.David F. » Mon Sep 13, 2004 3:21 pm

It seems to me to be an interference pattern of two dissimilar light sources. Perhaps a mercury light and a sodium based lamp.

J.David F.

Professor Lewin's picture

Post by J.David F. » Mon Sep 13, 2004 3:25 pm

It seems to me to be an interference pattern of two dissimilar light sources. Perhaps a mercury light and a sodium based lamp.

regiroux

The Glory

Post by regiroux » Mon Sep 13, 2004 3:39 pm


Ed

Post by Ed » Mon Sep 13, 2004 3:39 pm

I believe this is called a glory and is found mostly at high altitudes. It's formed by ice particles reflecting sunlight (the central brightness) and appears like a halo. Thus the name "Glory."

Am I even close?

Naresh

Post by Naresh » Mon Sep 13, 2004 3:46 pm

The phenomenon is 'The Glory'. Its the same thing happening with the August 6, 2004 APOD.

HJKeats

APOD for September 13, 2004 - Professor Lewin's challenge

Post by HJKeats » Mon Sep 13, 2004 3:48 pm

I enjoy APOD everyday and this kind of interaction is great.

My guess would be that it is a diffusion of sunlight coming from a magnifying lens for object viewing such as the camera that Professor is holding.

I remember as a child using a magnifying glass to burn holes in paper and if you hold it far enough away it would expand into a circular pattern much like in the APOD photograph.

If you examine closely the centre of the circle is near where the viewing lens for the camera is to.

Thanks,

Hayward Keats…

rhonda

heiligenschein

Post by rhonda » Mon Sep 13, 2004 4:09 pm

The photographer has captured a Glory, a "halo" of back-scattered light from small water droplets. The German word for it is heiligenschein, also called the Spectre of the Brocken. See APOD of 2004 August 6.

sruhl

Post by sruhl » Mon Sep 13, 2004 4:15 pm

I believe the answer is far simpler. The image is a projection of the sun through the viewfinder of the camera. The rainbow fring in the result of normal refraction through the lens.

John W.

Professor Lewin's challenge

Post by John W. » Mon Sep 13, 2004 4:35 pm

I think the professor was out for a bike ride on Sunday morning when he came across this. He's wearing a bike helmet! The wheel marks show where he rode over the spot when he first saw the phenomenon.

As reported by most people, it is most likely a Glory/Rainbow caused by visibeads or some other reflective material on the ground. The professor was only out for a ride. He didn't do any tricks to create this! It was there when he rode over it.

Rainbows are brighter in the center of the arc with the center of the circle being the observers head.

http://my.unidata.ucar.edu/content/staf ... /rnbw.html


Ahecht already give this web site on the visibeads.
http://www.pottersbeads.com/markets/hig ... sibead.asp

Stephen Hauskins

Walter Lwein's APOD

Post by Stephen Hauskins » Mon Sep 13, 2004 4:47 pm

This is essentially the same thing as a rainbow.

If you apply Snell's law you will find the various critical angles of refraction for red and blue light, rough 42 and 40 degrees respectively.

The white area is the reflection of white light within the critical angles above.

This is exactly how a rainbow is formed, with red on the outside and blue on inside.

I would venture to guess that if you measure that angle as viewed from the center of where the picture is taken that you will find red at 42 degrees approximately.

If you look at a single drop of water and apply snell's law you will see this phenomenon....

Stephen Hauskins
University of California, Santa Cruz
stephen@acg.ucsc.edu

RupertPupkin
Asternaut
Posts: 2
Joined: Mon Sep 13, 2004 4:43 pm

Post by RupertPupkin » Mon Sep 13, 2004 4:48 pm

May I point out sruhl that if it were a projection through the viewfinder of the camera his shadow would not be included, unless of course he were holding the camera behind his head.

EL_Kabong

Brocken Spectre

Post by EL_Kabong » Mon Sep 13, 2004 4:53 pm

...it's a Brocken Spectre. :shock:

George T

The Asterisk

Post by George T » Mon Sep 13, 2004 4:59 pm

The light circle is a perfect circle relative to the camera, and it's obvious that the light source is behind. Therefore something must generating a bright circle and rainbow regardless of the viewing angle.

Any shadow casting object or focusing source from above would be affected by the viewing angle - and create and ellipse.

A glory is created from water in the air. He's too close to the ground for enough water air to create a glory. The best explaination lies in refraction at the ground surface. This does create a perfect circle because the light refracted at the ground would scatter light consistently, and the view colors change with the angle offset from the source light.

Since light refracts more with are larger angle of incidence. A very shallow angle of incidents results in almost no refractions, and more of a direct reflections - i.e. pure white light. Hence bright center and colored halo.

Dan Mt Shasta, Ca.

its ..

Post by Dan Mt Shasta, Ca. » Mon Sep 13, 2004 5:00 pm

A picture from the spacewalk on the ISS..

RupertPupkin
Asternaut
Posts: 2
Joined: Mon Sep 13, 2004 4:43 pm

Post by RupertPupkin » Mon Sep 13, 2004 5:07 pm

Perhaps he's holding a child's bubble wand in front of the lens and the rainbow effect is caused by the soap solution. All this water on the ground talk seems far-fetched, it looks like the surface of mars.

stargazerdan

APOD 9-13-04

Post by stargazerdan » Mon Sep 13, 2004 5:17 pm

The picture is a glory (kinda) simular to the ones seen from airplanes looking away from Sun towards clouds or haze. The center is the reflection of sunlight back at you (same as in the brighter area inside a rainbow) and the colored circle is a rainbow but the arc is completed.

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bystander
Apathetic Retiree
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APOD - Identify this Phenomenon

Post by bystander » Mon Sep 13, 2004 5:18 pm

Very similar picture with an explanation following at http://www.geocities.com/CapeCanaveral/ ... t.html#TLP