APOD: Unusual Light Pillars Over Latvia (2009 Jan 12)

[nick.rassenti]

I'm am an architect.

I can't help noticing that the fanning pattern occurs primarily over what seem to be streetlights and not other light sources.

Street lights have an unusual light distribution pattern very different from simple point sources. They are designed so that in an array they will spread light evenly along the street. You will notice that when you walk directly under a street light that the light level actually falls off a bit, as if the luminaire has a blind spot. Maybe this has something to do with the fanned light pillars imaged by the ice fog.

[neufer]

I'm am an architect.

I can't help noticing that the fanning pattern occurs primarily over what seem to be streetlights and not other light sources.

Street lights have an unusual light distribution pattern very different from simple point sources. They are designed so that in an array they will spread light evenly along the street. You will notice that when you walk directly under a street light that the light level actually falls off a bit, as if the luminaire has a blind spot. Maybe this has something to do with the fanned light pillars imaged by the ice fog.

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. _The Adventure of the Six Napoleons_
........................................
"I wish to call your attention very particularly to the position
of this house, in the garden of which the bust was destroyed."
.
Lestrade looked about him.
.
"It was an empty house, and so he knew that
he would not be disturbed in the garden."
.
"Yes, but there is another empty house farther up the street
which he must have passed before he came to this one. Why did he
not break it there, since it is evident that every yard that he
carried it increased the risk of someone meeting him?"
.
"I give it up," said Lestrade.
.
Holmes pointed to the street lamp above our heads.
.
"He could see what he was doing here, and he could not there.
That was his reason."
.
"By Jove! that's true," said the detective. "Now that I come to
think of it, Dr. Barnicot's bust was broken not far from his red
lamp. Well, Mr. Holmes, what are we to do with that fact?"
.
"To remember it--to docket it.
We may come on something later which will bear upon it."
----------------------------------------------

[Trode]

This is one "cool" image . As one above has mentioned I to imediatly thought of Lightning "sprites" though there is little of that phenonama to apply here . I do agree with the above suggestion comparing the beam spread to "spotlight spread" pattern of stage lights . The light energy of the beem is concentrated ,hence brightest, where narrowly focused . Then the intensity drops off as one would expect with the spread/difusion past the focal point ....Trode

[Myriam]

hello!
I red only part of the readers proposals but my gess is more a camera optical effect than an atmospheric optical one.
When working on the picture with paint shop pro before joining you, I saw that the picture was shot outdoors through a stone window (no glass), see left side.
However, the camera was neither parallel to the first frame plan (right side is not so sharp than left one) and maybe nor to the pillars plan and this angle could have produced a sort of fish eye effet. The light are beginning to diverge where the "stone" frame is converging. the deepfield between the stone frame and the pillars and the difference in scale may explained the different angles.
What did the photograph really saw ?
Will we have a feedback about the more credible option ?

I take this oppotunity to thank APOD team for the always marvellous and challenging daily pictures.
Myriam . Belgium

[Aviator67]

Notice the convergence point toward the top of the image indicating considerable perspective distortion. This image was apparently shot through a window and I would agree with previous posts, perhaps a car or a train. The influence of a curved surface between the camera and the lights shouldn't be overlooked.

[james]

Unusual Light Pillars Over Latvia 2009-01-12

My best guess is that the light refracting ice crystals are dispersing the light above a focal point where the column is no longer visible from the camera's vantage point. A view from a higher elevation should confirm this guess.

The ice crystals are probably shaped much like a lens and focus the light straight up, but imperfections in the lens cause some of the light to be refracted horizontally. Multiply this effect by the number of ice crystals hanging in the air and you should see the phenomena shown.

The ice crystals are refracting the light horizontally, which is why the column is visible to the side. Much of the light is also being directed straight up through the transparent ice crystals to a focal point above which there is not enough light being refracted horizontally downward to be visible to the camera. The arcs above the focal point are where the ice crystals are refracting the horizontally refracted light from the column downward enough to be visible to the camera.

Again, this is my best guess.

Blessed are the Cracked for they let in the Light
james

[Myriam]

Hello, it is me again with a another approach than yesterday and closer to some readers' comments .

I thing that the light pillars' shape could be due to a spherical aberration of an imperfect lens situated inside the light pillar (top of the street lampin glass? ice cristals ) and pictured externally, meaning not as circles as it is currently the case when the camera/telescope lens situated inside the primary beam of light is to be blamed.
see
http://commons.wikimedia.org/wiki/File: ... tion_2.svg

when you rotate the bottom scheme of the wiki picture 90°left, it corresponds very well to the Latvian pillars, in particular the white one which shows the lighter part in the middle of the top of the beam of light and the read beam with its enlarged bottom part.

Myriam . Brussels

[Don Stoner]

I've cleaned up my earlier suggestion which was posted here, added some pictures and links, and generally tried to make it easier to follow. I've turned it into a web page which is now posted here. - Don Stoner

[pilotmba]

This is my first time for something like this.

I have read most of the other comments. I think several people are quite close to the correct explanation.

First, the two brightest pillars are not the only ones. The image has many verticals of varying degrees of brightness. As to the two most prominent, it's possible that the source lights have a strong "lobe" pointing upward. But the real question is what causes the opening-out of the beam towards the top. Again, I think several respondents were close, especially in pointing out that the beam seems to narrow to a focal point before it flares out. My refinement to the discussion is to point out that as the beams go higher, our visual perspective becomes more and more "underneath" the beam, so optically the flare appears to get broader. Light's straight-line travel continues until scattered by something -- air molecules, ice crystals, etc. So the scattering by the ice crystals is of course a probable cause.

GW

[ianrusselluk]

My guess is that it's a sub-zero cloud of flat, hexagonal ice-crystal platelets. Held in a stable condition below a layer of very slightly warmer air as often happens on a clear, frosty night (at least one star seems to be visible in the photo). In such still conditions the flat crystals would tend to orient themselves horizontally as they very slowly fall downwards through the air. This orientation would account for the vertical pillars of reflected light, as most light is reflected at 90 degrees to the orientation of the crystals.

It looks to me as if the 'trumpet-shaped' top of each pillar is near the upper boundary of the air-mass containing the ice crystals. This could be due to the horizontal orientation of the crystals increasing uniformly with increasing distance from the upper edge of the ice-cloud. The higher the proportion of non-horizontal crystals in the cloud, the wider the 'pillar' of reflected light.

One would expect crystals at the top of the cloud to be less oriented because these would be more recently-formed ones that are just beginning their slow gravitational descent. The stillness of the air would account for the mathematical perfection of the trumpet-shaped curves. If my guess is right, these curves are actually graphs showing the proportion of horizontally oriented crystals against altitude.

Ian Russell
http://www.interactives.co.uk

[alter-ego]

Hello,

Here is my two-bits towards understanding the light pillars - I've only read a couple of replies but I couldn't help diving into HaloSim to uncover halo behavior, especially related to light pillars

Long story short: Ice crystals have it. To first order, a combination of ice plates and horizontal columns can simulate the Latvian light pillars, even to the pronged flares. No lensing or optical distortion needs to be introduced. The angular dimensions of the simulation are also close to the real pillar.

The link below shows the HaloSim simulation and the light pillar image that has Cygnus stars & Vega visible. The angular scales for the picture and the simulation are matched (within ~10%). Based on the visible stars in the picture, the HaloSim scale was set via the zoom. FYI, the time of the exposure was ~11:45pm Latvian time (don't exactily know the horizon).

http://picasaweb.google.com/okubet/APOD ... 587538/img

Details & Discussion
Here's the breaout of the (thankfully) simple model: I used 20% Flat Plates & 80% Hexagonal Horizontal Columns. The plates were needed to get pillar extension, and the columns were needed to create the structured flare. The trick to the structure is to reduce the "c/a" aspect ratio in HaloSim. By letting c/a=> 1 (or so), the transition from 3-prong structure to a more uniform, filled in flare. Also, it looks like the HaloSim source size wants to be <0.5deg. I used an 0.4deg source diameter at -10deg elevation. There is quite a bit of "play" between the halo parameters, but the dominant features of the light pillars required two kinds of ice crystals to get close.

The simulation source is ~6 degrees below the actual source; the best I can tell. Given that I'm using HaloSim to model a totally different source than the sun (both in divergence and subtended source angle), I was totally surprised how close the simulation is to the picture. However, I was not surprised about the trend for source elevations to be <0 deg because the light reaching our eyes (from a light pillar) is reflected downward, therefore, light incident on the ice crystals is upward going (i.e. source is at negative elevation).

In conclusion, methodically using HaloSim to search for light-pillar behavior, I landed on a relatively simple solution that is very close to the real Latvian light pillar. Close enough, in fact, that I believe ONLY ice crystals and their orientation are needed to explain the Latvian examples. Nothing more complicated is needed for the primary ice pillar features. However, close inspection of the ice-pillar pictures to reveal fine structure detail not simulated. Also, variation is ice-crystal densities between the observer and the source are not modeled in HaloSim. Density differences could affect the size and/or shape of the pillars, and as I said, I don't expect the simulated source location to be correct.

Is the model a lucky coincidence? I don't think so. It's those phenomenal ice crystals!

[paulogram]

I believe it has to do with the density of the ice crystals ... I would think that the ice crystals slow down in the thicker air closer to the ground and therefor bunch up (akin to a layer of fog blanketing the ground), being more dense and reflecting a thinner column of light down low... but at a certain height above the lower ground layer of dense air & crystals is a layer where the ice crystals become less dense in a gradient fashion ...perhaps temperature gradient assisted by a breeeze at the higher altitude (closer to the ground the air is more still) ... the less dense the ice crystals ... the wider the reflection pattern causing the fan shaped top of column

[pilotmba]

I'm afraid I have to disagree with "paulogram." The denser the dispersion medium, the greater the scattering -- not the other way around. I still stick with my theory that the density of ice crystals may be quite uniform throughout the vertical cross-section, and that the fanning of the light beams towards the top is a matter of our perspective changing as we look towards the top of the columns. Also, I am not sure that the geometry of the individual ice crystals is a variable, as long as the geometry is fairly similar bottom-to-top. I can reproduce the same effect on a misty night with a well-focused flashlight. Try it. Take a flashlight out on a foggy night and shine it in any direction. The beam seems to open up non-linearly the farther it gets from the flashlight. Dispersion media will do that, since it has more and more of an effect the farther the beam penetrates through it.

GW

[tidman]

give that the light sources are unchanging, and ice particals are variable. seems the "reflections" are different due to a special arrangement of the reflectors (ice crystals). might this be a demonstration of an electro-magnetic field present, where in the charges on the ice (water is a polar molecule) formed in a precise temp, and pressure, causes them to align in that layer in a uniform pattern...resulting in a uniform reflection to the viewer. The "flare at the tops would be the level where the field is weakening or the crystals are not formed in their polar arrangement.
Tidman

[dennis]

I think the fanning is due to a moisture gradient falling off rapidly moving upward from where the fanning starts.

[RandyT5194]

If the phenomenon is related to light focusing patterns (and not to crystal refractions/reflections), then the phenomenon should appear on any night with a hint of fog or other suspended material.

If related to the optics of the window, then it should not appear from another window, or from an uninterrupted light path.

[ah-glow]

I noticed the icing on the trees, and the sodium vapor image had a purple diagonal line radiating up-left from the bottom (source?). Even if the lamps were coated with ice, most lamps have some sort of structure blocking the direct upward projection of the light, so therefore, I believe the light is not a beam eminating straight upward, but, instead a reflection of the ice crystals, (angle between the the viewer and the light source). What boslters this is a number of street lights in the relative foreground that do not have such "pillars"; I believe this is not occurring because the ice crystals do not form an appropriate angled relationship.

[Jafo55]

I saw this phenomenon on the morning of January 12th, at about 05:30am EST on my way to work in Canton, MI. At first I thought they were some kind of auroral display but the were appearing only in the south over certain sub-divisions (the road I was driving had only farmland on its north side). I could not actually see the light sources as they were blocked by intervening trees and houses. So, these "Light-Sicles" (yes, that's what I called them) seem to be hanging in the air! I am so glad that someone was actually able capture these "light-sicles" and share them.
Mark S Deprest
University Lowbrow Astronomers

[webolife]

Whether it's the temperature gradient of astrolabe or the wind shear mixing factor of pmanson, these two explanations make the most physical sense to me. This is clearly an optical/lensing event, and a movie of the event might be insightful as to the wind option. I wonder if the photographer has offered any insights from the original observation?
I prefer the temp gradient explanation as I believe these phenomena most often occur in stable air. With an increase in temperature per altitude would come the deformation of the hexagonal ice crystals responsible for the pillar effect, and the dispersal of the reflections would result in the arcky appearance of the pillar tops.

[bobpoblo]

I have not read through all the posts, but here is my theory on this.

Because the ice crystals do not fall as fast as rain, they tend to float down to earth. As they float farther down toward the surface they should slow and build up enough in density to develop a layer that you can see (like many other weather effects). That layer of density is the top of the beam, the arch portion. The density layer of the ice crystals toward the top of the beam disperses over a few meters and ends at the top of the light arch. The light is not visible anymore above the arch because the ice crystals are not dense enough to reflect the light visibly. The temperature is causing the density level.



As to the reason why there is an arch at the top. My theory is that because the density of ice crystals nearest the light source is high, there is a lot of reflecting going on in that area. The area by the bulb as a result spreads the source light by using each ice crystal within a short range of the bulb to intensify the light. So now, we have a main beam pointing directly up, with an ambient glow around the bulb pointing light in all directions.

Using filtering and photo effects I brought out a conic shape emanating from the light source that points upward. The cone’s tip is at the edge of the ice crystal density layer many meters above the light.



If we continue the edge lines of the cone past the tip and make a reverse cone opening upward, it takes the shape of the arch in question. The actual ‘bending’ of the arch is a result of rapid density loss at the edge of the layer.



I officially coin my Theory as, “Blair’s ambient conic light arch effect.” – Blair Burkhardt - Thursday 2/5/2009

*EDIT: First, it also appears the air is very still. Secondly, I believe the picture was taken outside. The line on the left side is actually a brick wall, while the line on the right is unrecognizable and out of focus.

[enorbet2]

I'm not going to be much help with the answer because I see light, other than that generated by lasers, having the natural property of "fanning out". I am much more baffled by how it is possible that the pillars appear to be at all coherent and fairly constant in width for such a long distance. Like in a few posts I am quite interested in discovering if the photo was taken through any intervening material whether glass or a screen. It would also be helpful if there were more than one POV , such as from underneath looking up and the opposing view, looking down. Very interesting photos and subject matter.

[bobpoblo]

Experiment: Perhaps the ambient light theory could be tested by blocking some of the light being emitted from the light pole. Specifically, by placing a shield on a horizontal plane around the top of the light pole. Imagine the tree in the picture below as the top of the light pole where the bulb is located.



The light shield could be maneuvered lower or higher on a vertical axis with respect to the bulb’s position.

If the beam of light in the center remains the same, but the arch of light at the top of the beam disappears then the theory may be correct, or possibly lead to another observation explaining the arch.

Any thoughts?

[nextonenon]

They also appeared over central Ohio. I counted 12 slightly less vivid but quite certainly the same thing on February 4th around 9pm. They stayed visible until dawn. I've never seen anything like it before or since.

n

[makc]

hey.... it's actually me in that picture, top row, 3rd from the right.

[apodman]

hey.... it's actually me in that picture, top row, 3rd from the right.

Up the Line (1969) by Robert Silverberg: Time travel tour guides see more of themselves every time they lead another tour to a major event in the past. Why they didn't see them all the first time is a question for Capt. Janeway whom temporal mechanics give a headache. Reader warning: Up the Line is sf, but some may consider it a dirty book.