A possible new halo above Moilanen arc

By Marko Riikonen

A simple diamond dust display that I photographed on the 6th of this month in Rovaniemi, shows above the Moilanen arc another, weaker V-shape. As I uploaded the photo on Taivaanvahti, I was not conscious of the effect, it caught the sharp eye of Panu Lahtinen and Reima Eresmaa who commented on it. Then some photo processing made it stand out more clearly. The version above was worked by Nicolas Lefaudeux. It is a stack of 13 images taken during 125 seconds.

If the effect is indeed real, it can not be accounted for by any known halos. At 10:26-10:27 am when the photos were taken, sun was too high (5.6-5.7 degrees) for reflected Parry to explain it and there is no normal Parry arc or tangent arc in any case.

Soon after I posted the photo on Taivaanvahti, it turned out this has been recognized already years earlier. Marko Mikkilä and Jari Luomanen photographed displays with a brightening above the Moilanen arc, respectively in 2007 and 2014. Both had informed other enthusiasts about the effect in their images, but these failed to create excitement at the time. Now, with the latest display’s somewhat better defined V-shaped arc, these older observations certainly deserve a new look.

One more case of interest is that by Timo Martola in the township of Janakkala last winter. His display contains a V-shaped arc above Moilanen arc, however, because the sun elevation is just right for reflected Parry (4 degrees) and there is also normal Parry and tangent arc, everyone has been content with reflected Parry explanation. Probably that’s what it really is, the display looks much like an earlier one that has a definitive reflected Parry. But with the new observation, we can now entertain the possibility of another explanation for the arc in Martola’s images.

A search of all Moilanen arc photos would be in place to see if more candidates turn up.

The original version from which Lahtinen and Eresmaa noticed the effect.

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.