Saturday, December 08, 2007

New home for Halo Reports

Because users are increasingly unhappy about the terms of use for the Blogger, we have decided to move the Halo Reports to another server. The new home is at the Ursa Astronomical Association server. Veikko Mäkelä made all the ground work. No more postings can be done to Halo Reports here, at the Blogger. With time, we try to move the old postings to new home so that the Halo Reports here at Blogger could be permanently removed.

The panorama is from Rovaniemi in the end of November.

Wednesday, December 05, 2007

Sky Haloes in Southern Germany

Although this year only few haloes appeared over Germany, I could observe the second complex halo display on Mt. Wendelstein. In the morning I saw my first subsun in this year, which appeared in freezing fog. Later a veil of cirrostratus from a low pressure area over the Mediterranean Sea crossed the Alps from the south. Under those weather conditions, large halo displays can be seen very often. In my own statistics, 80% of all larger halo displays appeared when there was a southerly stream of air over the Alps, or under foehn conditions. And also this time there was a large choice of haloes in the southern part of the sky, which lasted for about two hours and a half. Between 10.10 and 12.45 CET the 22°-halo, a bright upper tangent arc and a faint Parry arc, both sundogs with Lowitz arcs, the parhelic circle, an almost complete supralateral arc, a faint infralateral arc on the right side, and a complete sun pillar were visible. Unfortunately, the haloes appeared only over a small area on the northern rim of the Alps. So except of me, only my husband who was down in the valley at that time, could enjoy similar haloes.

Tuesday, December 04, 2007

More photos from three weeks ago in Rovaniemi

It seems putting the photos of the recent displays to my web page will delay. So, in a meanwhile here are two more photos of the display three weeks back.

When light source is at 0° elevation, some difficulties arises in identifying certain halos. Tricker arc and subanthelic arc merge together, as do helic and subhelic arcs. However, the subanthelic arc is formed by Parry-oriented crystals, while Tricker arc is from singly oriented columns. Because in this display the 46° supralateral arc is rather strong, and there are only weak indications of 46° Parry or Tape arcs, probably singly oriented columns were in command. The even brightness of the Tricker/subanthelic loop is also typical for Tricker arc. Subanthelic arc has strong brightenings on the sides - at least in the simulations - and that is actually what seems to be present in the the display of last weekend.

The reason why halos are seen so strongly in the halogen light is probably the relatively dark background sky as compared to sun or moon situation. Yet all the halogen lamp displays that I have photographed so far have been hampered by city lights. Once the crystal cloud drifts to the dark outskirts of the city, more intense appearances should be expected.

Monday, December 03, 2007

More results from the latest display in Rovaniemi

Here is some more material from the diamond dust in Rovaniemi three nights ago. After the heaviest Parry-crystal bombarding was over, Moilanen arc appeared, as shown in the photo on the left. Moon gives the beauty spot.

I have crystal photos from this stage, but as usual, they give no clue to Moilanen arc. In the earlier Parry-stage there was no indication of Moilanen arc whatsoever, but I did not manage to get the crystals. This bugs, because comparing the samples might have pushed us forward in solving the mystery.

The upper left image shows parhelia from streetlamp - the stripes that are parallel to the electric lines. Then there are also arcs extending slightly obliquely downwards. While visually parhelia curved towards me, these other arcs curved away and around me. As far as I understand from looking at divergent light simulations by Lars Gislen et. al, this effect is a 120° parhelion. In the photo only the brightest part of 120° parhelia is seen, visually the crystal glitter extented much further. Also a full parhelic circle was seen visually.

The lower left photo shows what was seen around the half moon at its best. For long time there was hardly no moon halo, although in the beam of the halogen torch a great display was present. Some indication of Lowitz arcs is present in the moon photo. The crystal sample may be representative of this stage, but I am not sure.

Saturday, December 01, 2007

Another halogen lamp display from Rovaniemi

A bright halogen spotlight and diamond dust is a magic combination.
Spot yourself exactly in the middle of the beam and breathtaking halo views may rewards you. An outsider will see just somebody bathing in the light and may wonder what is going on. There might be a Moon in the sky at the same time - like in the case shown here - but it shows hardly no halos at all. The lamp creates its own universe of halos.

The Ounasvaara snow guns created this display last night in Rovaniemi in the beam of a Cyclops Thor Platinum X-15 halogen lamp. Because of the lack of 46° lateral arcs, this display must have been dominated by Parry crystals. Indeed, in the lower right image there are both upper and lower Tape arcs as an indication of Parry orientation.

An interesting feature is seen in the images on left (the lower image is an unsharp masked from the upper). There seems to be a loop inside the helic arc. Much like the loop formed by the subanthelic arc.

On the upper right is a simulation that shows a quite similar loop (arrow). The crystals in simulation are Parry oriented and they are semitriangular, a half way between a triangle and regular hexagon. The thing in the photo looks to me like a halo and it might be the one shown in the simulation. I have not raytraced it, so I don't know what it might be called. There are some differences in the loop sizes between the simulation and the photos, but then again the projections are not exatly the same.

A bit more could be said about the results of the last night, but this must do for now. The simulation was made with a program by Jukka Ruoskanen.