Identifying light sources responsible for “floating” pillars

Recently, artificial light pillars were reported from Kuopio, Finland, which machted a city map projected into the sky. Artificial light halos are much less common in the German lowlands, especially in mild stages of the winter.

The more exciting it is, when nonetheless pillars from streetlights appear under such conditions. Of course they do not reach to the bottom then for the lack of crystals near the ground. This happened to me when cycling from a neighbouring village (Meuro) to my home (Hörlitz) in the Lower Lusatia region, on December 06th, 2018, a little after midnight (at air temperatures around -2 °C…-1 °C). My way led through a recultivated open coal mine (at roughly 51.53° N, 13.94° E), and I stopped twice to take photos of pillar segments that were floating in the sky at elevations of about 10°…25° in eastern directions. Their brightness was not great, as they were visible only in the dark outside villages and it took exposure times of about 30 s (at f/3.5 – f/4 and ISO 1600 on a Pentax K-5 camera) for decent photographs. The intensity also fluctuated over typically 30 s, depending on the changing number of properly oriented crystals at the right spot, so is a great hobby to watch these lights from certain points, another great hobby is play video games like WoW Classic as you can easily get gold for this online, read more here.

(00:33 CET, position A, f = 20 mm)

(00:49 CET, position B, f = 40 mm)

Of course, a very interesting question is where the responsible light sources were located. Under the assumption that the reflecting faces of the ice crystals are perfectly horizontally oriented, the light pillar is confined to a single azimuth coinciding with the the one of the source at the horizon, though the source itself may be rather far off and not visible. Luckily, some stars could be identified in the pictures from both observing positions (A and B), so the azimuths of the pillars can be determined. The brightest white pillar (1) higher in the sky and the brigthest yellow pillar (2) from the lower fence-like structure were chosen for further analysis:

(00:33, position A)

(00:44, position B)

When plotting the azimuthal directions from the two observation locations, intersections at 18.3 km (pillar 1) and 26.5 km (pillar 2) distance are obtained. These fit with the southern edge of the still active Welzow coal mine, and the Schwarze Pumpe power plant.

As the crystal positions, projected to the ground, are located halfway between the observer and the light source (see sketch below), they can be drawn on the map as well. The gray area above the lakes “Sedlitzer See” and “Partwitzer See” marks these locations as deduced from the pillar observations, though of course no actual boundaries of this area can be determined from this simple two-point study.

With the bottom distance d to the light sources known, it is straightforward to calculate the height H of the crystals above ground from the elevation angle h by simple trigonometry. The white pillar 1 in the image taken at 00:44 from spot B extended about 17.6° – 24.1° in elevation, and the yellow pillar 2 about 13.2° – 17.0°. It follows that the crystals were located at heights between 3.0 km and 4.1 km.

It should be added that earlier that night (Dec 5th, 20-21 CET), similar pillars were observed by Sören Petersen at Hohwacht, Schleswig-Holstein, at the Baltic sea. The distance to my location amounts to almost 400 km. Maybe the weather conditions favored the existence of a bigger ice crystal field at that time, as the rarity of such pillar observations in Germany renders a purely random coincidence unlikely.

The Fichtelberg halo display from December 18th, 2017

Over the past years, the Fichtelberg – Keilberg/Klínovec twin peak region in the German / Czech ore mountains has proven to be an unexpectedly active place for diamond dust halos. As shown in a recent study by Claudia Hinz et al., this high halo activity may have already been present there for decades or even longer, resulting in local myths but sadly few scientific reports in the halo literature up to several years ago.

Another exceptional display was observed on the top of the Fichtelberg (1215 m) on December 18th, 2017, by Gerd Franze, the head of the local meteorological station. He took about 400 photographs from about 12.20 to 13.20 CET (at sun elevations from 16.0° to 14.3°). During the course of the display, the temperature increased from –3.6 °C to its peak value of –1.9 °C at 13:10, followed by a decline down to –5.0 °C over the subsequent hour. Wind was noticed only at very low speeds of about 2-4 m/s coming from between southern and southwestern directions. Fog from the bohemian basin was drifting over the mountain top the whole day. No snow guns were running, as there already was enough natural snow for skiing.

a) view towards the sun, b) view towards the anthelion, c) and d) corresponding simulations using the parameters below

Simulation parameters for HaloPoint 2.0

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Reflection subsun in Southern Finland

6th January, 2017, I observed quite a clear reflection subsun in the southern Finland.

It was morning,  local time around 11am. I looked outside and saw a nice sun pillar. And clouds, that were about to block the Sun. So I went to take photos of the pillar before it was too late.

I got the pictures and stayed for a while and saw the clouds running over the Sun. Surprisingly, the pillar didnt disappear. I waited for a little while longer but the halo was stubborn. Then I realized, the source was not the Sun, directly, but its reflection! The sea is a couple of miles away and wasnt yet frozen (map).

More pictures can be found here.

Author: Matti Helin, near Turku, Southwest Finland

Thin plates in rotating Parry orientation as an explanation for the display on the night of 8/9 November, 2016, in Rovaniemi

8-9nov-taulukko-valmisIn an earlier post I told simulation attempts were not succesful for this display. Well, I really did not put that much effort into it. Now I have given it a fresh look and managed to get some succees.

The problem was the subhelic arc and anthelic arcs that could not be get rid of. In new simulations made with HaloPoint the subhelic arc issue is pretty much resolved and the anthelic arcs also play it low key.

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On some aspects of a display observed in Rovaniemi on the night of 9/10 November, 2016

This was a good no-hassle night of diamond dust hunt. The swarm was stationary and I didn’t have to pack up every 20 minutes to follow its whims. During the 6 hours of observing it was necessary to move only once. Also, both two locations were quite good concerning the light pollution. Especially the second place, where I wrapped it up in the morning ours, had a really dark segment which I used to light up the anthelic region.

As for the halos, the start of the night at around midnight was not so inspiring. As I arrived to the snow deposit area near the river, a sneak peek in beam revealed a run-of-the-mill plate display and I though it will just get worse because the temperatures were in the bad range, around -15 C. So I decided I might as well give some minutes for the half-moon display that had a smudge of Moilanen arc. In photographs it was transformed into a nice V-shape.

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A distinct Wegener but other reflection halos from column orientation lacking

58408_e6b1bf173a772112c7ee827c1b4a106fSpotlight displays are great in that almost every time you photograph them, you realize you understand halos less and less. This time the puzzle is: Why Wegener in the image above is so strong in comparison to other reflection halos? No subhelic arc is visible and neither there seems to be diffuse arc I think the spikes at the subanthelic point are lamp artefacts. Of course I can’t not say that for sure, but around the subanthelic point even weak stuff shows up easily to the eye, so had there been diffuse arcs, I should have noticed it. If we accept this, then, in addition to the Wegener, the only suggestion of column reflection halos is what looks like a short patch of Tricker arc cutting across the sub-Kern arc (see the simulation below for comparison).

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A plate spotlight display on 5th November 2016

average-valmis6Showcasing the last winter’s spotlight displays is still under way, but fresh produce is already coming in. Here is the new crop that I harvested on the evening of 5th November in Rovaniemi. In the image above the lamp is around -6 degrees below the horizon and both parhelic and subparhelic circle are visible. Slight intensity enhancements in them on the side of the sky opposite to the lamp are suggestive of Liljequist parhelia. Included are also Sub-Kern and sub-120° parhelion. I did not spot sub-Kern this time, but the latter was quite discernible when running alongside the beam. As usual, it was a pale pillar of light in which no individual crystals were detectable – very different from the intense subparhelic circle patch towards the subanthelic point, which is always made of pure glitter.

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Diamond dust halos in spotlight beam in the evening of December 2, 2015

45921_3bfac9da40b093f7ff4ab1552ac073a8Here are shown the rest of the photos from the night that yielded the second capture of the anomalous Wegener/Hastings. From the golf course parking lot, where we took those photos, we walked into the golf course, and were able to place the lamp even lower down.

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