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

[spectro1955]

The source of the light in not monochromatic. What you are seeing are the differences the different wavelength have due to the refraction of light through the crystal that also acts as a prism.

[spruce]

It seems that the dispersion occurs at the same height above ground (regardless of the light colour!) which suggests a strong temperature inversion at this height. Refraction, or bending, of the light beams due to the air temperature/density changing suddenly is my suggestion. Whatever the cause it sure is an impressive sight.
Spruce

[collie147]

I'd say this is very similar to light pillars or sundogs i.e. the hexagonal ice crystals in the air. But as for the flairing at the top, I would assume this is due to the lensing effect of these crystals. If you look at the line that they create up from the light source, obviously this would be different for each individual looking at the mini light pillars, as it is a subjective view much the same as a rainbow, they seem to come into full focus (i.e. the pillars narrow) just before they taper off and they widen and blur just below this narrowing down as far as the light source itself.

The position of where they narrow I would assume is due to the height of the crystals themselves, and that they are quite low to the ground and that resulted in the tapering of the pillars being quite early on in the pillars and quite acute.

[Kalvin]

Wondering if heat from these lights is causing the ice crystals to rise rather than fall --- not all lights are causing creating this effect --- perhaps these are hotter lights --- maybe a fountain effect at the top at a thermal layers edge ---

[Lasse H]

There are many wild ideas presented in this discussion: newly found arcs, focusing of light beams, bending of light in air, refraction within crystals, diffusion in an in-between window, just an optical illusion, etc.
- The basic explanation must be the one that pmanson gives. Horizontal ice crystals give a vertical pillar, and above a certain height they are not quite horizontal anymore, hence the fanning out.
- What remains to be explained is :
1. Why there appears to be a narrowing of the pillar just before the fanning out. Why the 'strangling' at this height ? (Below this point the pillar is slightly wider and more diffuse - and above this point it suddenly starts expanding)
2. Why the the fanning is not smooth. More specifically, the central pillar is still there within the fan, but added to it there is the conical fan. So there would have to exist horizontal ice crystals plus not quite horizontal ones.

[painta250]

there seems to be a two phenominon happening at the same time the problem being that each negates the other, still, flat and horizontal ice crystals explain the coloumn quite nicely. a fountain effect of heat rising from the lights explains the fans, especially when you look at how close the fan is to the clouds and the smoothness of it. but a heat fountain would distrub the ice crystals. so could there be a similar fountain effect that can rise up through ice crystals (without distrubing them) but not through clouds. there is also the point that if it is the crystals reflecting the light then why do the colomns not go down as well? unless the air is too turbulant below the lights.

just had a though. what if the clouds are falling, and pushing the ice crystals apart. it would be interesting to know how long this sight lasted and have other metological data but that seems like a possiblity, it would explain the pressence of the colomn within the cone and the pinching at the base of the fan, as the (obviously delicate and thin) latice of ice flexes under the pressure it would converge. to explain why this effect happens over the lights i would say its down to the heat creating a funnel for this effect to occur in.
still it is a mystry beyond my knowledge or expertise (not that i have any)

Painta

[gary91045]

Would it help to have a comparison image radius 90-degrees from each other, or from a significant height?

[Indigo_Sunrise]

Does anyone else wonder why the effect is only seen on two of the light pillars? Kalvin touched on it, when s/he said, "not all lights are causing creating this effect". It seems that whatever the cause, it's rather 'localized'.

Interesting image.

[pacfandave]

Not having majored (or even minored for that matter) in physics, or whatever science is required to explain this, I can but hazard a guess. The farther light travels from its source, the more dispersed it becomes. Could not the flair be explained by this dispersal?[quote][/quote]

[madtom1999]

I believe the pillar is caused by light reflecting of horizontally oriented flat crystals.
Someone might like to see if they can calculate the angle that the trumpet starts but I would imagine that this is caused by light reflecting/refracting off the far edge of these crystals and is only visible where the reflection from the bottom face of the crystal is reduced - there does appear to be a more solid column of light just below the trumpet which fades as the view gets more 'inline', where the light is a lot more scattered due to a similar process to the trumpet but with more background scatter.

[Jim in NC/USA]

A couple of folks are on the right tract, I believe. As a pilot, I've seen changes in moisture content at various altitudes that change visual appearances of clouds, fog, etc. My sense of the dramatic and beautiful photo is that at 100 feet or so where the light pillars widen out is a level where the density of ice particles forming in the atmosphere decreases. I do not think there is any illusion involved.

[PMJ]

On the assumption that this is how the scene appeared to an unaided eye, and that no intervening mediuum such as a glass pane created the illusion, Id guess that the ice crystals scatter the light over a small angle. Some part of the light would be transmitted, and some reflected. Above a particular angle, you would start to see light directly reflected (& scatered) from the lower face of the ice crystals. The higer the angle, the more of the directly reflected light would become visible to the observer, creating a flared effect above that angle. Below a certain angle, this reflected scattered light would not reach the observer. Just a thought on an intriguing & beautiful picture.

[Lasse H]

In response to this question (quoted below), the simple answer would be that the two pillars that visibly show the trumpets, are also the brightest ones over the two brightest lamps. The fan or trumpet itself is not as bright as is the pillar below, so the phenomenon of fanning is therefore more easily visible when the lamp i bright. I think.

As for the difference in colors, that someone pointed out earlier, the right one is obviously a high pressure mercury arc with its characteristic green/bluish white. The left one would be a high pressure sodium lamp, with a much warmer, almost coppery color. There are other mercury lamps in the picture that seem to shine bright (esp. one to the right), but without having any pillars at all. Probably they have a covering on top. For a light pillar to form, the lamp has to be open upwards.

Does anyone else wonder why the effect is only seen on two of the light pillars? Kalvin touched on it, when s/he said, "not all lights are causing creating this effect". It seems that whatever the cause, it's rather 'localized'.

Interesting image.

[woppledorf]

I think we are all missing a basic point here. These are not actually pillars. They look like they are pillars that rise up from the lights, but they aren't. There was an example posted earlier that has a diagram of where the light actually is in relation to the source and observer:
http://www.atoptics.co.uk/halo/lpil.htm

However, this diagram is neither complet nor acurate. The angles of the light rays when bisected do not produce vertical lines. This means that the placement of the crystals that would effectively reflect the light to the observer are incorrect. I don't have the means of producing a diagram, but if anyone does, I am sure that it would show that there are crystals at every point between the observer and source that will reflect the light to the observer. So obviously there is a concentration of reflection from specific locations between the two. If we can work out where that concentration is on a 3D diagrm, I am sure we could explain the fan phenomenon.

[mesaxi]

The lights seem to fan out at the cloud line. Perhaps that they're reaching a more densely moist area is the reason they're fanning.

[ccullar]

No one has mentioned the black angular shape on the far right edge of the image which indicated, I presume, that the image was possibly taken from inside and shot at an angle through a sheet of glass. I'm wondering if the effect at the top of the columns might not just be a phenomenon caused by the window?

[orin stepanek]

I'm not claiming to know what causes the pillars; but it sure makes nice art! 8)

Orin

[Lasse H]

Thank you woppledorf for pointing out the fact that the pillars are vrtual, and that the crystals could be anywhere! I am enclosing a photo taken a week ago on my balcony. You see a pillar of light below the sun. Small icy snow flakes form a pillar. Some are even in front of the balcony rail.

To ccullar:
Take a look at the other photos under the link 'above image and several similar images'! There are no windows visible there. The pillar phenomenon as such is very well known. The new thing here is only the two trumpets.

[prw]

I have to agree with ccullar on how these pillars were formed. The photo was taken from inside. You can see a slight fanning out of the lower pillars. The main pillars are from the brightest lights, reaching higher up, therefore being altered by the window.

Having worked in the Arctic as a weatherman for 1-1/2 years, I saw ice crystals all the time. Never did I see anything quite like this.

Be interesting to have had other photo's taken from other areas & from outside to see if the same effect is recorded.

[trekbike]

My guess is like many others. The density of the ice crystals is greater closer to the ground and a change in temperature as the light moves skyward causing gradally fanning or scattering of the light. The word temperature inversion came to mind. I hadn't thought about wind causing the crystals to be stirred up. The pattern is very consistent for fanning due to wind.

[bobhyatt]

Perhaps the temperature of the atmosphere at different elevations causes the ice crystals to be very well aligned (i.e. horizontal) near the ground where the air is coldest and most stable, creating narrow light columns, and less well-aligned at higher elevations where the air is warmer and more turbulent, causing the light to be more dispersed?

[Charlie Garrett]

I haven't taken the time to read all the posts, so I hope I'm not duplicating anyone. The flaring of the pillars appears to be the outline of the tops of a low level fog. We often have fog here in Sarasota and it will go to a certain height, after which it ends. This fog isn't a straight blanket, but has curves in it similar to the bumps on clouds. If you'll notice, some of the pillars continue straight up, while others flare in different amounts indicating a more abrupt or lesser curve of the cloud at that particular point. Above the more dense fog you can see clear skies and even stars. Whatever - let me know if I win the big smart-guy prize...

[dimple]

I have nothing to add about the pillars themselves, but there is a black bar on the left of the picture which has a defined but irregular edge. This suggests that the picture was not taken through the window of a vehicle, although it may have been taken from inside a building or under a roof of some sort. Also, the black bar on the right does not have a clearly defined edge, so I doubt it is caused by a solid object--maybe it is a shadow? I also note that there are a few stars visible above the pillars.

[David]

I believe the phenomena is a result of the angle we are viewing it. If it is falling crystals that are roughly oriented horizontally then the greater the angle from horizontal the more light will be reflected. If someone could take 2 pictures, one directly above the other separated by enough distance to make it obvious(or not) that the cone starts at the SAME ANGLE FROM HORIZONTAL, then we would know whether or not the cone has a specific height or is simply a function of the angle.
Most places in the world sundogs or pillars don't happen at ground level but far away and the light source, the sun or moon, is a very far distance.

[orin stepanek]

I have nothing to add about the pillars themselves, but there is a black bar on the left of the picture which has a defined but irregular edge. This suggests that the picture was not taken through the window of a vehicle, although it may have been taken from inside a building or under a roof of some sort. Also, the black bar on the right does not have a clearly defined edge, so I doubt it is caused by a solid object--maybe it is a shadow? I also note that there are a few stars visible above the pillars.

Could the black bar be caused by the fact that there may not be any lights there?

Orin