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View Full Version : APOD-Contest: Identify this Phenomenon



kucharek
2004-Sep-13, 09:16 AM
Identify this Phenomenon (http://antwrp.gsfc.nasa.gov/apod/ap040913.html)

Jay should have a field day with this :D

jt-3d
2004-Sep-13, 09:18 AM
Clearly it's a spot light behind the photographer.

Ut
2004-Sep-13, 12:44 PM
You know, I think I've actually seen this before. I don't remember clearly, but I just have a strong sense of deja vu while looking at the picture. I think it was on dry, discoloured pavement.

gritmonger
2004-Sep-13, 12:50 PM
It's that German word- on the tip of my tongue- Gegenschein: same as when mountaneers would see their shadow in the middle of a complete circular rainbow, can be seen when flying in an airplane, opposite the direction of the sun...

Normandy6644
2004-Sep-13, 01:15 PM
Very cool picture nonetheless.

Gmann
2004-Sep-13, 01:15 PM
Perhaps it's some kind of Heiligenschien, which I recall is proof that we didn't actually go to the Moon if you follow Bart Siebrel's line of logic, which is similar in shape to a failed field sobriety test...but that is a matter for another forum.

Seriously, I believe it is a picture taken with the Sun directly behind the photographer. The ground is a black material mixed with clear crystals that create the lighter area, and the prism effect on the perimeter of the lighter area.

wackywizjr
2004-Sep-13, 02:09 PM
Perhaps it's some kind of Heiligenschien, which I recall is proof that we didn't actually go to the Moon if you follow Bart Siebrel's line of logic, which is similar in shape to a failed field sobriety test...but that is a matter for another forum.

Seriously, I believe it is a picture taken with the Sun directly behind the photographer. The ground is a black material mixed with clear crystals that create the lighter area, and the prism effect on the perimeter of the lighter area.

I think you are close =D> \:D/ , The white dust on the ground looks like Bead Blasting remains :-k . That would be the dust left over from using microscopic glass beads to sand blast. I have seen this effect before in the back lot of the place I used to work. I believe it is caused by light difraction and reflection off of the cracked surfaces of the beads.

Gmann
2004-Sep-13, 02:23 PM
I sent in my reply, with your glass bead theory to the address on the picture. If I get the "Nobel prize for fizziks" I'll split it with ya :D

Andromeda321
2004-Sep-13, 07:17 PM
Ok I'm no expert in prisims so I won't attempt an answer. But I can't help but point out to people that it's rather interesting if you click on the "students" "colleagues and "APOD editors" links. :D

wackywizjr
2004-Sep-13, 07:30 PM
Check out this link 8)

http://www.geocities.com/CapeCanaveral/Launchpad/5320/minnaert.html#TLP

It explains the effect better than I can 8-[ .

Dark Helmet
2004-Sep-14, 03:36 AM
sun-balls.

Fighter pilots plac
e them of an enemy plane, and can then attack without beeing seen*

*well, they are visible, but you can't look at them of your eyes water up, because you are looking at the sun.

Eroica
2004-Sep-14, 04:10 PM
I'm going to say that the bright centre is an example of Heiligenschein, while the rainbow ring is a glory produced by the light of his camera flash being backscattered by dewdrops on the ground.

Betenoire
2004-Sep-14, 05:11 PM
Also called a Brochen's Specter (and my spelling is atrocious), right?

mike alexander
2004-Sep-15, 12:07 AM
If I assume that the picture was taken by the camera held in the picture, then the only way I can think of getting it is by standing in front of a reflecting surface (imagine standing in a room in front of a mirror and snapping a shot. You MUST be looking at the lens in this photo, otherwise how could the picture exist?).

The light source is approximately specular and behind the photographer's head, so he's in shadow.

The streaks and goobers I don't know, but they look like out-of-focus junk. Perhaps the shot was taken through a dirty window fairly close to the lens with a mirror or other reflecting surface further behind it.

The color ring would be a glory, maybe from scratches or stuff on the glass. It would be in front of the photographer as he looked at it (glory in front, light directly behind), superimposed on the reflected outline image.

Or, maybe it's a Martian Saint :o

Eroica
2004-Sep-15, 10:50 AM
If I assume that the picture was taken by the camera held in the picture, then the only way I can think of getting it is by standing in front of a reflecting surface (imagine standing in a room in front of a mirror and snapping a shot. You MUST be looking at the lens in this photo, otherwise how could the picture exist?).

I assumed that the photographer was looking down at his shadow on the ground.

Incidentally, I think that wackywizjr may be on to something with his "Bead Blasting remains", which makes better sense than dewdrops (otherwise why tell us that the photo was taken at a construction site?).

mike alexander
2004-Sep-15, 05:07 PM
And NEVER try to analyze ambiguous data when you are tired/distracted. :-?

I'm sticking with thew Martian Saint theory for now.

gromit
2004-Sep-15, 05:57 PM
Everybody is assuming the ground is flat. If the ground was bowl shaped we should get a similar reflection. If you look in the center of the light there appears to be a lot of dirt confirming my suspicions that it is picture of a depression.

mike alexander
2004-Sep-15, 08:04 PM
Wait. I conditionally recant my recantation.

Since the only image-viewing software I have on my computer here is Paint (!) I used the invert function, making the silhouetted black outline white. Turns out I think I can see some structure in there, especially what looks like a rectangle and circle at eye level. If that's the camera, then it can't just be a shadow on the ground.

Can someone with Photoshop or similar bump up the gamma or modify the tone map to see if there is any detail in there? If so, then it can't be a shadow and has to be a reflection.

(edit)

I fooled around a bit with Microsoft Photo editor (lower gamma to 0.1, increase contrast) and can see what looks like a camera.

I don't have any way to link to a local server to show the picture. Can I send it to anyone who can?

Eroica
2004-Oct-05, 04:56 PM
Apparently, it's not a glory, Brocken Spectre, or Heiligenschein!


Glories (=Heiligenschein=Brocken Spectre) are produced by mist, fog and clouds (they can often be seen when your plane is flying over clouds). Dew on grass can also cause a glory. The colors are washed out; they are never as crisp and well localized as the colors in my picture.

Donnie B.
2004-Oct-05, 05:29 PM
All I can say for sure is that Walter Lewin seems to have a haircut inspired by Muppet Labs employee Beaker. :wink:

01101001
2004-Dec-11, 10:22 AM
Dang. It's an effect of glass bead-blasting media (http://space.mit.edu/~lewin/apod/).

That was my guess -- sure, no, really! -- but I didn't record it and I certainly couldn't explain all the details Lewin requested.

But, I had seen it before, when out for a walk I encountered similar retroreflective beads on the road as a result of a crosswalk striping job.

I constantly kick myself for not gathering up a few handfuls of them. I have several times since wished I had some for various projects and only see them available on the Web in, like, 50-pound bags. I always keep looking for a paint crew I can "borrow" a cup of beads from.

Congratulations to wackywizjr (http://www.badastronomy.com/phpBB/viewtopic.php?p=330893#330893)!


I have seen this effect before the white powder on the ground is sand blasting beads.

Andromeda321
2004-Dec-11, 06:14 PM
So was anyone here one of the thousands of people who wrote to him? I was, got a response after three or so weeks. My answer was partly on the right track, though, so he said I had "quite an imagination" and had I been in his MIT class he'd've given me some extra credit. 8)

SAMU
2004-Dec-11, 10:07 PM
It's just a rainbow. Ordinarily you can only see part of the circle and you can't usually see a shadow of your head because it's usually cloudy when it rains. But you can see this any time the sun is out by spraying a fine mist of water from your garden hose with the sun to your back. The center of the rainbow circle is the shadow of your head.The prism is formed in a rainbow by the surfaces of the droplets that are at an angle to the lense of your eye. Thats why the rainbow is centered on your head, because the rainbow is really just in your eye or, in this case, the film of the camera.

In fact, in conditions where you can see the shadow of your head, since the light wavelengths are strongly seperated, the frequencies are also concentrated on the places where they fall in your eye. So you can feel a rainbow in your eye that way. It feels kind of like when you have been swimming in chlorinated water and look at lights.

It's a fun gimick to play on someone to say "Have you ever felt a rainbow?" You just get them to look at the shadow of their head and ask if they can feel it.

Spacewriter
2004-Dec-11, 10:26 PM
yeh. I saw this before. Doesn't the answer involve chalk or blasting powder?

;)

01101001
2004-Dec-11, 10:53 PM
yeh. I saw this before. Doesn't the answer involve chalk or blasting powder?
I revived the thread (http://www.badastronomy.com/phpBB/viewtopic.php?p=379272#379272) when I posted a link to Lewin's official answer (http://space.mit.edu/~lewin/apod/).