2016. február 20., szombat

Diamond dust halos on the night of 12/13 January – part I


With this post starts the presentation of January 12/13 night results. All the photos are from the beam. The image above is a singe frame with 30s exposure. Just basic halos there. In the gallery images the emphasis is on the column 3-5-7 which shows up in crystals of psychedelic colors. The individual frames are all 30s exposures. The lamp is the usual 5 degrees below horizon.

Marko Riikonen

[gallery ids="1770,1771,1772,1773,1768" columns="5"]

Halos from oriented pyramids in the spotlight beam

The night of 20/21 January came with oriented pyramid crystal halos also in the beam. The image above is the last breath of a world class odd radius display that got us completely unawares. This is the first time this winter that the odd radius stuff was visually crystal clear in the beam. Colored and solid upper and lower 9° plate arcs were seen, but if they were still present when the camera was placed in the beam, they are nevertheless washed out by the overexposure. As the lamp was at negative elevation of about 5 degrees, that makes the lower 9° plate arc the 23-6 type. The odd radii stuff was all gone in the next shot which would have had the exposure right. In this precious one one still sees the 35° halo and of the oriented pyramids the lower 20° plate arc.

We drove around and switched on the lamp here and there, stubbornly trying to get a rerun, but to no avail. Diamond dust was already on the retreat, the air was drying up even though it was around -33° C. Yet we managed to get something just before it all evaporated, as shown by the first image in the gallery. A little simulation study (second image) was necessary to see whether it was column or plate pyramid stuff, but that did not give definitive answer. The plate scenario simulations are identical except that in one is 22° halo and in the other 23°. The stuff immediately inside the 22-23° halo and the 35° stuff was noticed initially visually.

That stacking series was taken at 3:30 am. The last two photos in the gallery are the first photos of the night at 6 pm. We photographed these lunar and beam displays simultaneously. No odd radii yet at this early hour.

Marko Riikonen / Jarmo Moilanen

[gallery ids="1751,1752,1754,1755" columns="4"]


Pyramid crystals and odd radius halos, part II



More halo and crystal photos from the 20/21 January night. While this second crystal sampling and photographing session was under way, the display in the beam was photographed constantly, but again odd radius halos are not visible in the photos, expect perhaps for a suggestion of 35° halo at one stage (not shown). Yet again the sample was littered with classical pyramids as shown by the images in the gallery.

The picture above is an appearance of odd radius halos after the crystal business was over with. It is a br of stack with total of 9m30s exposure and contains 9°, 18° and 35° halos. Three more halo images are in the gallery, first a single frame from the stack above, then two that are versions of another stack, the br displaying full 46° halo.

Jarmo Moilanen / Marko Riikonen

[gallery ids="1737,1736,1733,1732,1734,1735,1738" columns="4"]

Pyramid crystals and odd radius halos, part I


The night of January 20/21 in Rovaniemi was a night of odd radius halos. Here are shown mostly crystals collected during a half hour period. At the same time photos were taken continuously in the beam, in the gallery below is one of those stacks. The sample contained plenty of traditional type pyramids – something we have not yet seen this winter. So it is curious that odd radius halos are not conspicuous in the beam images and at times even completely absent. Maybe the abundant cavities in the crystals caused too much disturbance.

The stack is from a stage where the odd radius stuff was at its best, taken towards the end of the crystal collecting period. Visible are 9°, 18° and 35° halos. The temperature during the night was around -33° C.

Marko Riikonen / Jarmo Moilanen

[gallery ids="1714,1713,1712,1711,1710,1709,1716" columns="4"]

Lunar odd radius display in diamond dust


On four out of last five winters Tapio Koski has photographed lunar diamond dust odd radius halos in the Rovaniemi area. These one-per-winter occurrences are almost solely responsible for lunar diamond dust odd radius displays photographed in Finland during those years. This winter we wanted take part in the tradition. Yet despite numerous odd radius displays we had harvested in the beam, those by the moon – or sun for that matter – were simply not on the offing.

Except on the night of 20/21 January, which was the month’s last diamond dust night in Rovaniemi. During the day, when driving in the city, we paid attention to Fairbanksian amber, a beautiful yellow glow in the sun direction which can be seen in cold weather and with which we became familiar on the succesful halo expedition to Fairbanks in January 1996. This gave us an omen of foreboding that a night of big odd radii diamond dust was finally on the cards for Rovaniemi. Weather forecast was with us too, as the temperature was expected to drop to -33° C – the magic number that Walt Tape has given as being in the center of the temperature range favorable for odd radii.

The display appeared as some thin water cloud that had momentarily overtaken the sky cleared away. The first halo visible was upper 23° plate arc, many others soon followed the suit. In the beam only a crappy plate dominated display was visible – the pyramid stuff was higher up.

Jarmo Moilanen / Marko Riikonen

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