After having been hunting diamond dust halos since darkfall, at 1 am we withdrew along with disappearing crystals back to aparment to sleep. But this did not mean calling it quits. The forecast was for the conditions getting better, so every one hour each of us woke up in their turn to check the situation.
This night conditions were overcast and we were watching halos in spotlight beam. But there was a moment when clouds all turned into ice crystals, allowing moon shine bright and make a passable display. We switched off the spotlight and managed to take some photos before it got cloudy again. Camera lenses were frosted, which caused some blurred areas and bright dots in the images.
Jarmo Moilanen, Marko Mikkilä, Marko Riikonen
On 23 November 2015, we were watching diamond dust halos develop under overcast skies in Rovaniemi. As we stood on a rectangular field a couple of hundred meters across, we followed halos slowly gather momentum in the spotlight beam, reaching climax when clouds were cleared away for a short while – and revealing at the same time also a lunar display. Here is an excerpt from Marko’s observation log written the next day:
“The display just adds gear. We are looking at beautiful subanthelic stuff, subanthelic arc, diffuse arc… It becomes monstrous when the cloud almost disappears. That is when we get also a moon display with full parhelic circle. No one seems to be in a rush to photograph the moon display. The beam display is sheer grotesquerity. The laser scapel sharp, 100% pure glitter of the tangent arc and uppervex Parry.”
The image above shows what looks like a patch of Wegener or Hastings on top of the 22° halo. But instead of having the usual horizontal curvature, it is bending slightly downwards. Because of the view angle, though, the effect is not as evident as it could be. Anyway, if it were standard Hastings or Wegener, it would curve steeper up in the photo.
We have no idea how it formed, our attempts at simulating have come up empty-handed. The display was seen in Rovaniemi on 23 November, 2015, and the arc appeared at a stage when the display was still progressing to reach its peak.
Nine days later, in the beginning of December, we got another, better sighting, suggesting it is not exceedingly rare. In a similar manner, it did not occur when the display was at its best, but when the display was undergoing a momentary low. We will post about this later.
Jarmo Moilanen, Marko Mikkilä, Marko Riikonen
Crystal samples should be englightening, but all too often they just make you confused. The observation I made on 22 November 2015 in Rovaniemi is a case on point, although an observation recently published by Alexander Haußmann may now provide a solution.
The mystery deepens. In two previous posts we wondered why some displays are great in their column orientation halos even though the crystals have well caved ends. Here we show a case that appeared on November 22, 2015 in Rovaniemi, where crystals seem not much different, yet rare halos requiring basal faces are completely absent. Even the 46° supralateral arc gives just a whiff. Poor crystal orientations can’t explain the absence of rare halos as the tanget arc is quite sharp. Had we known only about this display, we would be quite happy to explain with cavities, but knowing about the other displays, it is quite puzzling.
Marko Mikkilä, Jarmo Moilanen, Marko Riikonen
The four caleidoscopic arcs carry in their name the location on the celestial sphere where their loops’ cross. For three of these halos – helic arc, Tricker anthelic arc and subanthelic arc – there exists photos showing the crossing.
The diamond dust season is soon to arrive in Finland and it is time to wipe the dust off the equipment. In a meanwhile, here is the last winter’s starter for Rovaniemi, on October 30. The temperature during the display was -5° C, a quaranteed number for great stuff.
Here is divergent light subparhelia flanking the pillar. Spotlight displays are classical displays with little divergenness 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.
Jarmo Moilanen / Marko Riikonen