APOD: A Hall of Mountain Glory (2010 May 04)

[alter-ego]

I think the determining factors will ultimately be determined by physics. I think testable physical differences between fogbows and glories should decide this. Does anyone know of anything definitive that would clearly decide between the two possibilities in this case?

Rob,
I'd like to share my thoughts on this question. I finally found some time to catch up and focus on these a halos. It looks to me the Glory and Fogbow are night and day different, and I think Les' pictures are better for comparing these halos that the Wiki link, and I will go so far as to say that the Wiki article needs more work. It is short and incomplete. Given all the Fogbow pictures I've seen (all are different than the Glory), I believe Wiki is wrong to say "a fogbow has no colors." Also, the Wiki pictures are convoluted with simultaneous glory and fogbow halos.

With that said, here are my observations that strongly (and repeatably) differentiate the two halos:
1. A fogbow has it's brightest ring outside, with supernumeraries inside the primary ring and which are progressively fainter towards the antisolar point. A glory has the opposite; primary ring brightest nearest the antisolar point with secondary rings getting fainter moving away from the antisolar point
2. The color progression for the fogbow supernumeraries is also opposite of the glory secondary rings. For the fogbow, the red spectral band exists on the inside (toward the antisolar point) of the white band. For the glory, the red band exists on the outside of the white band.

Interestingly, the anitsolar point in the APOD picture is in the ground, just below a mound of rocks. Could there also be a glory? Maybe, but we don't know; the rings, they exist, are "behind" the outcropping. So, in my mind, the distinctions between a fogbow w/supernumeraries and a glory are clearly evident, and although I didn't duscuss pure physics parameters, I think basic characteristic differences do exist. Close observation reveals these and agree with the many pictures on Les' site. I hold a high regard for Les' knowledge in these matters, and, in all ways, I view his site for atmospheric phenomena as solid as the APOD site is for astronomy. Both are great sources for knowledge and entertainment.

[orin stepanek]

From Henry Sharpe's description: http://gdl.cdlr.strath.ac.uk/smcj/smcj014/smcj01408.htm I"d call it a glory. Seems as though; if it were a bow there would be separation between each.

[RJN]

After revisiting Les Cowley's impressive website, I now believe that the most likely explanation of the pictured phenomenon is a fogbow with an unusual amount of bright internal supernumeraries. In retrospect, I should have done more of my background research on his site and less on wikipedia. I would advise Les or others to update the wikipedia pages on glories and fogbows.

Although an unfortunate oversight, this was a good opportunity for me to learn more about an interesting area. Scientists in my view are ordinary people trying to make sense of extraordinary events, and like everyone we make mistakes. This is not the first APOD that I have erred, and surely it will not be the last.

Here is the science as I currently understand it. First, fogbows and glories are different physical phenomena. Fogbows are extensions of rainbows to fogs and clouds and are relatively well understood in terms of reflection and refraction. (The supernumeraries are perhaps less well understood.) Glories are less well understood but are generally thought to also include a significant amount of diffraction. Fogbows and glories can be individually very different because of different droplet size distributions.

Observationally, fogbows are almost always angularly larger than glories. Although both depend on water droplet size, fogbows, which are similar to common rainbows, may vary from 20 to 40 degrees in angular radius, while glories typically range from the central shadow to as much as 20 degrees. Now the angular size of the arcs on this APOD were not reported and hard to estimate from visual cues. Still, I will try to email the photographer and obtain this information. (If someone wants to do this first, please have at it.)

Next, it appears that glory arcs are brightest near the central shadow and the surrounding arcs are progressively less bright. In contrast (ha!), fogbows have their brightest arcs far from the center and have more faint arcs, called "supernumerary arcs", inside. An exception to this is a full "secondary fogbow" (caused by an additional internal reflection inside the drops, I think) which are well outside the primary fogbow and are more faint. (This was another reason why I thought this APOD featured a glory.) This, currently, is the main reason why I now feel that this APOD features a fogbow and not glories -- the internal arcs appear fainter like supernumerary arcs of a fogbow.

Color progression: this was not as clear to me as indicative to fogbows as it was to Alter-Ego (but thanks AE!). I found the colors too hard to track to be definitive. Perhaps if I expanded the image and went through it more carefully the color progression would more clearly indicate a fogbow.

I apologize for this mistake. I will fix the APOD probably sometime this weekend when I return home. I also apologize for the slow progress of my understanding, which I might blame on being on travel and so busy. I thank everyone for their points in the discussion, and would welcome even more comments. Putting my scientist hat back on, this and other unusual arc cases might make good "mini-papers" that would help future photographers (and scientists and science writers) better label and understand unusual atmospheric optical phenomena.

- RJN

[alex.tudorica]

Hello,

First I would like to thank you for the APOD, it was quite a surprise for me this time and I found out from some of my friends just before an important exam .

Second, I'd like to apologize because I checked and I didn't clearly specified in my email message the phenomenon that I photographed and neither useful technical details about the photograph (except for that it was taken trough a linear polarizing filter). I have checked now (roughly) and from the antisolar point to the middle of the exterior fogbow arc there are 37 degrees. The view was not very different visually from the picture, by post-processing I tried to get it as closest to what I had seen as possible. As I have a 17 mm lens for wide angle and a 1.6 crop factor digital camera I am trying to get wider images by making panoramas; this is the case for this image too, being composed out of four other.
It is actually one of the most impressive fogbows I've ever seen in the last 7 years, since I started to look for them. I counted 4 supernumerary arcs inside the main bow that time but usually I saw at most two. Here you can find an excellent image with many supernumeraries, "ending up" in a glory: http://www.atoptics.co.uk/fz343.htm
If you are going to change the caption for the picture this weekend, can you please also specify the location of the photograph? It was taken near the "Observatorio del Roque de Los Muchachos", La Palma, Canary islands.

Clear skies,

Alex Tudorica

[BillWhite36]

I have experienced The Glory many times while skydiving – from the plane, in freefall, and under the ‘chute. I got a big surprise falling into The Glory one noon:
Normally, as you approach something, it seems to get bigger. We expect to see that. But as I fell towards the glory, my shadow in the center got smaller.
BTW, clouds are WET inside, and they will fog up your goggles and altimeter!
BillWhite36

[neufer]

A Hall of Mountain Glory

Explanation: If you tried to enter this hall of fog, you would find it dissipates around you. The hall is actually an optical illusion created by sunlight backscattering off of a cloud passing below the peak of the mountain from which this picture was taken. Known as "the glory", the phenomenon is frequently seen from airplanes. The ring's center is not visible, but if it were, the shadow of the observer would appear. This shadow would likely change as clouds passed, creating a faux moving giant known as the Brocken Spectre. Pictured above, several concentric rings of the glory appear to create a hall for this mountain king.

Still waiting for correction.

A fog bow, solar glory and Brocken spectre at the Golden Gate Bridge in San Francisco.


A solar glory and the Brocken spectre observed in San Francisco.

[RJN]

I am finally back and have just made the correction. The main NASA APOD site now carries the corrected text. Mirror sites are advised to update their text to match. Once again I apologize for the oversight. - RJN

[bystander]

APOD: A Hall of Mountain Fogbows (2010 May 04)

If you tried to enter this hall of fog, you would find it dissipates around you. The hall is actually an optical illusion created by sunlight backscattering off of a cloud passing below the peak of the mountain from which this picture was taken. Known as a fogbow and similar in some ways to "the glory", the phenomenon is sometimes seen from airplanes. The ring's center appears near the image bottom where the shadow of the photographer is visible. This shadow would likely change as clouds passed, creating a faux moving giant known as the Brocken Spectre. In the picture, several concentric rings of the fogbow appear to create a hall for this mountain king. The cause of fogbow supernumeraries arcs and glories have only been understood recently and are relatively complex. Briefly, small droplets of water reflect, refract, and diffract sunlight backwards towards the Sun. Atmospheric backscattering phenomena have a counterpart in astronomy, where looking out from planet Earth in the direction opposite the Sun yields a bright spot called the gegenschein.

[DavidLeodis]

Thank you Robert for providing the corrected explanation. It is greatly appreciated.

The image does look like a view down a tunnel. It would be a fascinating experience if there actually was a colorful tunnel to walk through like that.

[neufer]

Thank you Robert for providing the corrected explanation. It is greatly appreciated.

The image does look like a view down a tunnel. It would be a fascinating experience if there actually was a colorful tunnel to walk through like that.

I regret if I have rushed you in any way on this, Robert.

The old version was wrong and somewhat confusing;
while the new version is simply confusing as hell, IMO.

I would recommend that you start from scratch and
drop ALL references to glories, Brocken Spectres and mountain kings.

Fog bows are closely akin to rainbows NOT GLORIES (and certainly NOT gegenschein).

[Chris Peterson]

Fog bows are closely akin to rainbows NOT GLORIES (and certainly NOT gegenschein).

Fogbows are similar to rainbows- both phenomena primarily associated with internal reflections in water droplets. Glories and gegenschein are similar, as both are primarily associated with scattering.

[owlice]

Fogbows: white on the outside, (sometimes) crunchy colored on the inside
Glories: colored on the outside, (possibly) white on the inside
Rainbows: just colors
Polychrome: daughter of the Rainbow

[neufer]

Fog bows are closely akin to rainbows NOT GLORIES (and certainly NOT gegenschein).

Fogbows are similar to rainbows- both phenomena primarily associated with internal reflections in water droplets.

<<Fogbows form in the same way as rainbows. A small fraction of the light entering
droplets is internally reflected once and emerges to form a large circle opposite the sun.

But... ...beyond that there are major differences. Rainbows are formed by raindrops which are so large that rays passing through them follow well defined 'geometrical optics' paths. Fogbows are formed by much smaller cloud and fog droplets which diffract light extensively. The emergent light is mostly deviated 135 to 150° from its incident direction to produce the main fogbow of 30 - 45° radius centered on the antisolar point. The deviation corresponds roughly to the geometric optics angle of minimum deviation of ~138° for the 42° radius rainbow.

Fogbows are almost white with faint reds on the outside and blues inside. The colours are so washed out because the bow in each colour is very broad and the colours overlap. Widely spaced supernumerary bows inside the main arc are produced by the constructive and destructive interference of overlapping wave crests along the main light path.


As the droplet diameter (shown above in microns) increases, the bow narrows and the inner supernumerary bows move closer together. Eventually, for raindrops larger than 1 mm diameter, diffraction effects become small and we have a rainbow with bright colours and hardly noticeable supernumeraries. Cloud and fog droplets rarely exceed 100 micron diameter. The bows intermediate in appearance from 100 - 500 micron dia. droplets are occasionally seen in the sprays of waterfalls.>>

[neufer]

Fogbows: white on the outside, (sometimes) crunchy colored on the inside

• 

• Arctic Fogbow

[alter-ego]

Fog bows are closely akin to rainbows NOT GLORIES (and certainly NOT gegenschein).

Fogbows are similar to rainbows- both phenomena primarily associated with internal reflections in water droplets. Glories and gegenschein are similar, as both are primarily associated with scattering.

Also, for all practical purposes, glories and gegenschein exist at the anti-solar point. In contrast, bows are centered on (but not at) the anti-solar point, so this similarity is less obvious.

[Chris Peterson]

Also, for all practical purposes, glories and gegenschein exist at the anti-solar point. In contrast, bows are centered on (but not at) the anti-solar point, so this similarity is less obvious.

I think it is clearer to say that all of these phenomena are centered on the anti-solar point. Rainbows and fogbows, because of the way that light is internally reflected in different sized water drops, show their most obvious effects at a large angle from their centers. Glories and gegenschein are the result of Mie scattering, which means that there are two strong scattering lobes, the largest in the direction of the light source (but this is normally invisible due to the light source itself), and the second at 180° to the light source. Therefore, these show their most obvious effects right at their centers. The fact that glories are produced by scattered light from water droplets, while the gegenschein is produced by scattered light from dust, doesn't make all that much difference. The dust will produce stronger back scatter, but the principle is the same.

[owlice]

Alex,

Thank you very much for the additional information on your lovely APOD! It's very nice to hear from the photographer himself!

neufer,

Fogbows: white on the outside, (sometimes) crunchy colored on the inside

• 

"If we took the bones out, it wouldn't be crunchy, would it?"

[smokehidesstars]

WHAT DOES IT MEAN!?!?!?

[Beyond]

I never thought that i would ever find so much information that i did not know about "OZ" in Apod. What an amazing place!

[owlice]

You didn't know about Polychrome, beyond?! She's a delightful character in Oz!

[Beyond]

just the two movies - the wizard of oz and the wiz.

[owlice]

Oh! They were books first, and in some cases, just.