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

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

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

Post by HJK » Mon Sep 13, 2004 3:09 pm

My guess would be that it is a diffusion of light 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.


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APOD - Identify this Phenomenon

Post by bystander » Mon Sep 13, 2004 5:28 pm

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


This is something very strange

Post by Blacky » Mon Sep 13, 2004 9:33 pm

This is what i would like to call explain the unexplained.

Considering the conditions in which the picture was taken, and knowing i haven't got to the optical lessons at physics i can only guess... :D

Well the source of light (Sun) apears to right above the point from which the picture was taken, and is also very very powerful, i think these are important clues and also the fact that the picture is taken of a flat surface ( at least it appears flat).

So from this to the conclusions... a difcult way.

Maybe the light that is reflected from the grownd somehow it is also reflected
in the camera's exposure lens. Something similar to puting two mirrors, one in front of another. An echo... i don't know.


My Hypothesis

Post by SCole » Mon Sep 13, 2004 9:55 pm

This looks like a phenomenon related to heiligenschein,
as the center of the circle, the lens of the camera and the sun are all aligned. The circular "rainbow" must be caused by small clear spheres of plastic or glass scattered on the pavement. I think such spheres are found in reflective paints used to mark traffic lanes on highways. The symmetry of the "rainbow" suggests uniformity in the shape of the refracting/reflecting elements. The particles act as raindrops do in forming a standard rainbow. White light enters, the various colors refract at different angles, reflect internally and are then projected back to the observer.


Sept 13 pic of the day

Post by dguzman » Mon Sep 13, 2004 11:47 pm

This appears to be a glory, or a colored difraction of rings around an (antisolar point) in this case, the professors head. Usually, glories can be seen on mountains or clouds and occasionally, if atmospheric conditions are right, they can be seen on or near the ground. (ie, when it is cold out). The reason is because the glory forms when light (sun) defracts, in most cases off mist, clouds, or even ones breath in cold weather. The size of these glories or magnificent light circles appear to be inversly proportional to the size of the cloud, mist or breath droplets.

Also, glories are always seen directly opposite the sun and thier rings are centered on the observer's shadow (the professor).


Fits of Reflection

Post by GreekJimbo » Sat Sep 18, 2004 6:50 am

I sent Dr. Lewin the following explaination. Curious to see if anyone agrees.

My guess is that your APOD is a perfect visual representation of the quantum effects of light reflecting off of several surfaces. In your picture's case, the surfaces are oil on water on concrete.


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Post by Dan Cordell » Thu Sep 23, 2004 4:33 am

Please keep all discussion related to Dr. Lewin's challenge in this thread.
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