Friday, 18 March 2016

Making divergent subparhelia with a spotlight


By Jarmo Moilanen and Marko Riikonen

Here is divergent light subparhelia flanking the pillar. Spotlight displays are classical displays with little divergentness involved. A way to create truly divergent halos with spotlight is to point it to the ground. The reflection from snow then acts as a divergent light source. Another way that might work is to cover the lamp glass with a layer of snow. That would be a shorter lasting solution, though, as the heat of the lamp will melt the snow.

Most spotlight halos are visibly formed of separate crystal glitter. Not the divergent parhelia. They are solid objects floating majestetically in the air. One feels humbled before their lofty heights, just as a lesser subject might feel in the presence of royalty.

Below is another photo of divergent subparhelia taken some hours later. And also a little lunar display from the same night, which was the 18/19 January night in Rovaniemi.

Wednesday, 16 March 2016

The hiding sub-120° parhelion


By Jarmo Moilanen and Marko Riikonen

Nothing out of the ordinary here. Just a plate display and its crystals. Visible are the usual folks: subcza, sub-Kern, sub-120° parhelion. The behaviour of the last one in spotlight displays is a little curious, though: while it comes out well in photos, visually it is cryptic. One has to run along the beam to see that ghostly spot of sub-120°. It is not made of big glitter like the sub-Liljequist parhelia – it does not seem to be made of much glitter at all, just faint diffuse spot of light.

Rovaniemi, in the morning hours of 19th January.

Monday, 14 March 2016

One display - three mysteries


By Jarmo Moilanen and Marko Riikonen

It is difficult to get a matching simulation of pretty much any spotlight display. Some details tend to be always wrong. But one can usually obtain what could be called an acceptable approximation of the real thing.

The shown display is a true rebel in this respect, for it comes with three anomalies too blatant to be swept under the rug. First, the subparhelia were brighter than parhelia (this we noticed also visually). Second, of the Schulthess arcs (the arcs from Lowitz orientation) only the concave component was visible. And third, there is no subparhelic circle opposite to the lamp.


We can not simulate any of these anomalies. The solitary presence of the Schulthess arc concave component is not a new thing, there exists a handful of such displays. The missing of subparhelic circle opposite to the lamp in this level of display is something unheard of, as is the inverted relative brightness of parhelia and subparhelia. In the simulation above (light source elevation -5 degrees) only plate oriented crystals were used. Below is a sample of the simulation crystal shape variation, the “mother shape” shown in the upper corner.



The display had also a weak segment of parhelic circle between subparhelia. The crystal shape shown above struck the right balance between the sub-Kern and the parhelic circle segment inside subparhelia.

The night was 18/19 January, the location the Sieriaapa bog in Rovaniemi. The temperature was – 29° C.

Sunday, 13 March 2016

Odd radius display and its crystals


By Jarmo Moilanen and Marko Riikonen

This odd radius display appeared on the night of 17/18 January in Rovaniemi at -29° C. Visible is the usual duo of 9° and 35° halos, and also what seems like 18° halo.

Crystals were collected. It is hard to make sense of most of the crystals. Many seem to have pyramid faces, but obvious pyramids were very few in the sample.




Friday, 11 March 2016

Streetlight parhelic circle on video


By Nicolas Lefaudeux,  Marko Mikkilä,  Marko Riikonen and Jarmo Moilanen

The image above opens a video of parhelic circle under streetlight. There has been some question on whether the three dimensional character of divergent light halos shows up on video, but at least here the vortex effect of the parhelic circle is tangible.

Likewise, dimensional effect of parhelia is well visible in another video. At the end of the clip the camera is panned to show also the Liljequist and sub-Liljequist parhelia. One more video. Downloading gives better quality.

These were seen on the night of 6/7 January in Rovaniemi. Below are two more images from the night’s action.

Wednesday, 9 March 2016

9° and 35° - not your expected combination of odd radius halos


By Marko Riikonen and Nicolas Lefaudeux

This display is far from being impressive. But it has an interesting combination of odd radius halos: 9° and 35°. Not something that would be expected from your textbook pyramid crystals. We had several displays in such a style this winter.

The display was seen on the night of 7/8 January in Rovaniemi in diamond dust that was being displaced by an increasing snowfall. The temperature at the official measuring site 7 km away was -27° C.

Monday, 7 March 2016

An unknown halo next to the sub-Kern arc


By Jarmo Moilanen, Marko Mikkilä, Nicolas Lefaudeux and Marko Riikonen

On the night of 6/7 January we had an anticipation that something unusual would occur in the beam because the temperature was forecast to drop below -30° C. It was clearly a dreamer’s thought, based only on the reason that no one had photographed snow gun originated diamond dust displays below that mark.

When we called it a wrap near the twilight hours, nothing out of the ordinary had happened. But after we woke up and started looking at the photos from the night’s plate displays, there was visible, next to the sub-Kern, an arc that we did not recognise. It was captured at two different locations with three hours passing in between.

Here are those two photos where the arc is seen. In addition, there is an anomalous looking bulge in the sub-Kern arc where the exotic arc is pointing at.

We don’t know how this new halo is formed, nor how to simulate it. It’s a one weird arc.

The lamp was at the usual -5 degree elevation.

Saturday, 5 March 2016

Circumhorizon arc in spotlight beam


By Jarmo Moilanen, Nicolas Lefaudeux, Marko Mikkilä and Marko Riikonen

It is not that unusual to see a circumhorizon arc under a streetlight, forming a striking spatial shape. On the night of 6/7 January  we gave circumhorizon arc a shot with spotlight as we arrived to a place where there were rather high piles of logs on top of which we could clamber while leaving the lamp on the ground below.

Whereas one usually just walks into the beam, here it was more a matter of sticking one’s head into the very narrow beam – narrow because the lamp was so close.

The circumhorizon arc was only crystal glitter, but it was conspicuous. The image above is a maximum stack of several individual photos. At the top is the subsun and a little underneath one may discern a vague blue horizontal line – the blue circle.


The blue circle is better picked up by br treatment as shown by the image on the left. The simulation next to it contains also sub-circumhorizon arc. Had we not placed the lamp so low (the simulation is for 67 degrees), we would have probably caught also the sub-circumhorizon arc. The crystals were probably too thin to produce it at this elevation.

The final photo shows the setting. The night was cold and at this location the night’s lowest, -35° C was felt.

Blue subsun


By Jarmo Moilanen, Marko Mikkilä, Marko Riikonen and Nicolas Lefaudeux

On the night of 6/7 January we gave a try also on another halo effect that simulations predict: the blue subsun. It is an effect in the blue spot and blue circle family and it colours the core of the subsun blue at 58.5 degree light source elevation.

We though we failed to photograph the effect and then forgot about it and were surprised when it turned out in other photos where we were actually aiming at subparhelic circle.

The lamp-camera configuration did not correspond with that optimal elevation of 58.5 degrees, but the blue subsun effect is nevertheless seen in outer areas of subsun in the two images we got. In the image above it is visible on the upper edge of the subsun and a matching simulation was found at 60.5 degree light source elevation. The grayscale br image highlights the blue of the subsun particularly well (bright white).

In another photo (below) the lamp was, according to simulation, at 57 degree elevation and the blue colour is on the other side of the subsun. Shown are also crystals collected during the display and uncropped images.

Friday, 4 March 2016

Catching a divergent light halo effect predicted by simulations



Sometimes it is possible to make a deliberate attempt to photograph something predicted by simulations. On the night of 6/7 January we made such an attempt on the diffuse spots of light that in simulations are seen next to the divergent light subparhelion.

The effect is formed by a mixture of subparhelic circle raypaths, including 3157 raypath and sub-120° parhelion raypath. Its exact shape and position depends significantly on the crystal shape, like for the Liljequist parhelia.

To obtain an omnidirectional secondary light source that was bright enough we pointed the lamp directly to the snow surface. We took photos, looked at them more closely the next day, and there it was – those smudges of light predicted by simulations.

The photo above is actually from a slightly better case on the night of 18/19 January. Next to it is a simulation. Below is the one on the 6/7th.

Nicolas Lefaudeux / Marko Riikonen / Jarmo Moilanen / Marko Mikkilä




Catching a divergent light halo effect predicted by simulations



Sometimes it is possible to make a deliberate attempt to photograph something predicted by simulations. On the night of 6/7 January we made such an attempt on the diffuse spots of light that in simulations are seen next to the divergent light subparhelion.

The effect is formed by a mixture of subparhelic circle raypaths, including 3157 raypath and sub-120° parhelion raypath. Its exact shape and position depends significantly on the crystal shape, like for the Liljequist parhelia.

To obtain an omnidirectional secondary light source that was bright enough we pointed the lamp directly to the snow surface. We took photos, looked at them more closely the next day, and there it was – those smudges of light predicted by simulations.

The photo above is actually from a slightly better case on the night of 18/19 January. Next to it is a simulation. Below is the one on the 6/7th.

Nicolas Lefaudeux / Marko Riikonen / Jarmo Moilanen / Marko Mikkilä




Wednesday, 2 March 2016

Odd radius display in spotlight beam



Here is a photo of a diamond dust odd radius display in the spotlight beam. Of the less commonly seen halos visible are lower 20° and upper 35° plate arcs.

The image which is a stack of several photos, was taken in Rovaniemi on the night of 6/7 January. The odd radius stuff seemed confined to this particular location, Rikanaapa bog, to which we paid several visits during the night. From our observations and the photos taken it looks like the display remained there pretty much unchanged through the whole long night. The crystal swarm originated from snow guns 6 km away.
The version above, which shows the halos best, is done with the “blue-minus-red” method. Below is also a version with minimal intervention and a one with an unsharp mask.
The display has lower 24° plate arcs and it seems like there may be the lower 9° too. As the lamp is about 5 degrees below the camera, that makes these plate arcs of the 23-5 and 23-6 type respectively. In other words, the B-components for these arcs, if you will.
Nicolas Lefaudeux / Marko Mikkilä / Jarmo Moilanen / Marko Riikonen