Odd radius display and its crystals


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.

Jarmo Moilanen / Marko Riikonen

Streelight parhelic circle on video


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.

Nicolas Lefaudeux / Marko Mikkilä / Marko Riikonen / Jarmo Moilanen

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


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.

Marko Riikonen / Nicolas Lefaudeux

An unknown halo next to the sub-Kern arc


On the night of 6/7 January we had this anticipation that something unusual will occur in the beam because the temperature was forecasted 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 wraps 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 recognize. 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.

Jarmo Moilanen / Marko Mikkilä / Nicolas Lefaudeux / Marko Riikonen


Circumhorizon arc in spotlight beam


It is not that unusual to see 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.

Jarmo Moilanen / Nicolas Lefaudeux / Marko Mikkilä / Marko Riikonen


Blue subsun


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 colors 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 color is on the other side of the subsun.  Shown are also crystals collected during the display and uncropped images.

Jarmo Moilanen / Marko Mikkilä / Marko Riikonen / Nicolas Lefaudeux



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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


Odd radius display in spotlight beam


Here is a photo of a diamond dust odd radius display in 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


Torch shaped Moilanen arc


The two images above, which are versions of one stacked image, show a torch shaped Moilanen arc. This is the shape that the halo takes when light source is about 9 degrees below horizon. Below is a simulation for that elevation.  Also shown is another photo in which the places of lamp and camera were switched, giving a more familiar looking Moilanen arc with the lamp about five degrees above the horizon. The display was photographed on the night of 5/6 January in Rovaniemi.

Marko Riikonen / Nicolas Lefaudeux

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Wegener or Hastings?

DSC_0269-0303This spotlight display that was photographed in Rovaniemi on the night of 5/6 January rises the question of whether it is Wegener or Hastings arc or both together that is seen here. From the outset, as there is helic arc but no subhelic arc one could argue that it is rather the uppervex Hastings arc.


When comparing with simulations (below) it does not look that obvious anymore. The curvature and extent of the arc looks more akin to Wegener than Hastings (the side view image). And it is possible to simulate Wegener without subhelic arc by using thin plates in column orientation. Indeed, to have best agreement with the images, in all simulations thin plates were used both in Parry and column orientation.

In the image on the left the crystal h/d is 0.1 for all simulations. In the one on the right it is h/d 0.03 for rotations of 0.5 and 5 degrees, for full rotation simulation h/d 0.1 was used. Crystals are triangular, oriented in Parry orientation so that the tip is pointing up.

Well, none of these simulations come out satisfying. The light source elevation for simulations is -5 degrees.

Marko Riikonen / Nicolas Lefaudeux

– added one more image with simulation containing both Wegener and Hastings