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APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 3:51 am
by APOD Robot
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. The cause of the glory has only been understood recently and is relatively complex.
Briefly, small droplets of water
reflect,
refract, and
diffract sunlight backwards towards the Sun. The
phenomenon has a counterpart in astronomy, where looking out from planet Earth in the direction opposite the Sun yields a bright spot called
the gegenschein.
[/b]
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 4:02 am
by Apollo16
The ring's center is not visible, but if it were, the shadow of the observer would appear.
Ah... yes it is and yes you do. Look at the bottom of the picture. You do see the shadow of the photographer.
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 4:47 am
by Astronut
Yes....You can see the Photographer's shadow and if you listen very closely, you may be just able to hear him starting to sing - Somewhere....over the rain-bow-bow-bow-bow..................
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 5:43 am
by alter-ego
APOD Robot wrote:The
phenomenon has a counterpart in astronomy, where looking out from planet Earth in the direction opposite the Sun yields a bright spot called
the gegenschein.
I like the photo, and I don't mean to quibble, but the gegenschein is far from a "bright spot". I believe a reasonable brightness estimate is ~6 magnitudes per square degree. Good skies are needed for this (as you can probably tell from the gegenschein link).
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 7:26 am
by Les Cowley
This is NOT a glory. The explanation is incorrect. It is a fogbow. A fogbow is similar to a rainbow but produced by small mist and fog droplets rather than raindrops. Significant diffraction occurs in the small droplets causing the bow to be diffuse, with weak color and multiple supernumeraries. See
http://www.atoptics.co.uk/droplets/fogbow.htm
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 7:47 am
by Radek
It is not a glory. It's a fogbow (a white rainbow) with supernumerary arcs. Great photo.
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 7:56 am
by boris the aphid
The first link in the explanation is broken, it is missing the <a> I think! Great picture though as always. APOD takes my breath away sometimes...
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 7:59 am
by agulesin
Interesting photo of a more interesting phenomenon, whatever it is called.
One thing I wondered is why the rings all have the same sequence of light colours? In a "normal" rainbow the secondary bow's colours are reversed relative to the primary. In this photo, they all seem to be in the same direction (even though looking at the monitor that closely hurts my eyes!).
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 8:06 am
by metleif
Radek wrote:It is not a glory. It's a fogbow (a white rainbow) with supernumerary arcs. Great photo.
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 8:18 am
by metleif
metleif wrote:Radek wrote:It is not a glory. It's a fogbow (a white rainbow) with supernumerary arcs. Great photo.
In a fogbow the radius of the main bow should be 42 deg. I doubt it is. A teleobjective has been used..
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 11:26 am
by HellCat
Whether or not it's a fogbow or glory, there's still a typo.
The hall is actually an the mountain from which this picture was taken.
So maybe it should be "on" the mountain?
And what IS the deal with the color sequence? Does this mean that each rainbow reflected back towards the viewer has its 'reversed' sequence reflected back in the opposite direction, another angle, or somehow suppressed?
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 12:02 pm
by Redbone
I do not believe that we correctly understand glories yet. I see them all the time, with or without clouds. When there is no cloud base to project upon, the colors are not visible, only a circular brightening. I believe that this is caused by light waves refracting around the plane. There does not seem to be a correlation to airspeed or relative humidity. As described, they may be quite complex and require moisture back-scattering to produce the rainbow effect, but the concentric brightening rings are present every time the sun is within a large angular window above the plane or other blocking object.
Nice picture!
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 12:47 pm
by Steve M
I have seen this effect while riding a motorcycle away from the sun in light fog. The halo around the head of the shadow is awe inspiring. It also is difficult an quite by chance to set up, I have yet to get a picture of it. Your photo is very nice and does capture the effect well.
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 1:11 pm
by jisles
Another related astronomical phenomenon is, I assume, the brightening of Saturn's rings at opposition (when the planet and the Sun are on opposite sides of the Earth). The rings are composed mainly of ice particles.
APOD May 4 - NOT A GLORY!
Posted: Tue May 04, 2010 2:24 pm
by Les Cowley
This is NOT a glory. The title and caption are incorrect. It is a fogbow. A fogbow is similar to a rainbow but produced by small mist and fog droplets rather than raindrops. Significant diffraction occurs in the small droplets causing the bow to be diffuse, with weak color and multiple supernumeraries. See
http://www.atoptics.co.uk/droplets/fogbow.htm
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 2:43 pm
by oannis
I agree with agulesin and hellcat, what is with the color sequence?
That's the first thing I noticed.
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 2:48 pm
by John Adam
I agree with Les Cowley - this is not a glory, it's a fogbow, with nice supernumeraries!
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 3:59 pm
by alter-ego
Les Cowley wrote:This is NOT a glory. The title and caption are incorrect. It is a fogbow. A fogbow is similar to a rainbow but produced by small mist and fog droplets rather than raindrops. Significant diffraction occurs in the small droplets causing the bow to be diffuse, with weak color and multiple supernumeraries. See
http://www.atoptics.co.uk/droplets/fogbow.htm
Les is an expert on halo phenomena. By default, I side with Les.
Leave it to me to miss the fun stuff
..
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 4:13 pm
by Myyk
I am wondering if this phenomenon is the same as when you are in a boat on a slightly murky lake and the sun is behind you and you see your shadow in the water and it appears as if there are rays of light emanating from the shadow, the rays look a bit like crepuscular rays. Has anyone else seen this. Also, just a guess, but I think the difference between this and a rainbow where the additional bows keep reversing the color sequence, is that you are between the source of light and the refraction so you only see the refraction that is reflected back at you, whereas with a rainbow you are down on the ground with the source of both the light and the refracting above you and you see both directions that the light is refracted in.
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 4:33 pm
by Chris Peterson
Myyk wrote:I am wondering if this phenomenon is the same as when you are in a boat on a slightly murky lake and the sun is behind you and you see your shadow in the water and it appears as if there are rays of light emanating from the shadow, the rays look a bit like crepuscular rays. Has anyone else seen this.
It isn't the same phenomenon. The fogbow is produced by refraction through water droplets, while the effect you are seeing in water is produced by scatter. That makes it very similar to a glory.
- IM2_12330p.jpg (32.95 KiB) Viewed 3388 times
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 5:04 pm
by RJN
Indeed, perhaps I erred in writing this APOD's caption. Still, it seems possible to me that a glory is actually pictured. Although cloud optics is not my subspecialty, while researching this topic, I was well aware of the fogbow possibility and investigated it. I was influenced by the wikipedia entry for Fogbow found here:
http://en.wikipedia.org/wiki/Fogbow. In this entry it says:
Unlike a glory, which has multiple pale colored rings caused by diffraction, the fogbow is entirely white. The fogbow's lack of colors is caused by the smaller water drops... so small that the quantum mechanical wavelength of light becomes important and smears out colors that would be created by larger rainbow water drops...[1]
So it seems to me that this APOD image indeed has multiple pale colored rings which are not completely white. So I concluded that this APOD featured a glory. Also, the published images of fogbows both on the above referenced wikipedia page and on previous APOD pages about fogbows do not match the above image as well as the previous APOD images of glories, in my opinion. (Please, though, gentle readers -- confirm this for yourselves.)
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?
Last, I am traveling and so cannot myself change this APOD caption until later this week. Still, if I am wrong, change it I will.
- RJN
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 7:19 pm
by orin stepanek
Whether or not it is a fog bow or glory; it makes an excellent background and that's good enough for me.
For now I'll go along with RJN's answer.
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Tue May 04, 2010 8:31 pm
by HellCat
These are links to the only two articles I could find on cloud droplet size distribution.
http://ramanlidar.gsfc.nasa.gov/activit ... teretc.pdf
http://langley.atmos.colostate.edu/publ ... I_1978.pdf
Is it possible that the fogbow and glory are the same phenomena with different droplets? Are the radii and reflective bands the same? Are the 'gaps' in this 'glory' filled with the missing inverse colors? And now that RJN has got me started, what's really going on inside those droplets?
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Wed May 05, 2010 2:33 am
by wyomom
This one is way-y-y- more realistic than Pacholka's APOD fogbow of 2010 February 2
Re: APOD: A Hall of Mountain Glory (2010 May 04)
Posted: Wed May 05, 2010 4:02 am
by alter-ego
Like you, I tend to gravitate towards pretty detailed articles, but in this case I think pictures and 2-D model predictions are worth thousands of words. If you haven't already, please check out Les' web site. I think the IRIS software available there is extremely useful to explore and create halos, and fun too. I mention this because in his "Formation" sections under Glory and Fogbow, there are great halo simulations revealing how droplet size affects the halo. Great stuff! Between the great pictures, and his descriptions (technical enough for most readers), Atmospheric Optics is a high quality, educational website. I really enjoy that site.