Hello everyone,
after several talks with Alec, I decided to make some digging into my old odd radius halos displays to search for rare halos and find out some more 28d halo (and 13d halos too).
Here are some examples of what I found so far that might be interesting to submit here to your assessment. I hope you will find those cases interesting.
For some of them, I still have all the raw files of the sequence, for others, I kept few raw images, but for all of them (exposed here at least) I made various time-lapses to keep sequence in B-R rendering, colour rendering, stacked with 4 or 8 images each, like the one I presented earlier in this blog.
I will start with a sharp display of odd radius circular halos I got last year, in April, at the morning.
I'm not usually an early bird so I can miss some nice displays each year. For this one I got the chance to have the display still available to start a capture from my roof window. The center of my house is a stair tower which offer a nice blocking roof for the spot I am from. Therefore, with the shaprness of the display, the 9° ring was particularly well visible on B-R rendering before the sun comes out of the roof (because the diffusion of the light on the lens add noise up to the 9° ring area).
There is a first image, B-R rendered from a sole raw image, to give a view of the sharpness of the event:
Stacking with the above one as first image, with the 25 following images makes those odd radius halos more clear:
Well, in the light of recent search for 28+° ring, this was one of my first tries even if I was expecting, like for the 13° halo, to find it when the rings are not sharp. But if you don't try, you won't find anything.
So there is a processing the the previous stack to enhance sharp halo first then eventually larger borders ones if any.
There is a folder on my drive, so you can take a look at the time-lapses of the day. As usual, better download it rather than viewing it as a Youtube video, to have a better video compression (as is the original one)
Many years ago, I got a nice odd radius display at sunset, during a day of November 2014. The view is not ideal, as I placed my camera on the edge of a window, look south, with a wide angle rectangular lens, hence the distortion. (EoS 1200D + Sigma 8-16mm, set at 8mm).
I was so amazed by the display I sent it to Nicolas Lefaudeux to have his expertise on the matter. And then he told me I caught the 28° halo, again (but I don't recall why this 'again') ;-)
There is the display, B-R rendered, and unsharp masked.
Unfortunatly, I did not keep any raw file of this event.
There is a folder where are all the remainings.
And any old how, here are some I cannot say it is, but looks like there might be something there.... or not:
And while browsing at all of those, I realized I got at least a dozen of 13° halos, with at least one with the Moon. Which could make a post after this one, for the record.
And a last one, not for the 28d spotting, but only because I like it a lot:
Now, a couple hours after starting this post, I think I may go get some rest ;-).
Greetings from France.
Nicolas R.
Showing posts with label 28° halo. Show all posts
Showing posts with label 28° halo. Show all posts
Thursday, 18 May 2023
Sunday, 30 April 2023
Odd radius display on sunset time, 2022-10-16 (Jouhe, France)
Often, when I see the clouds coming from west, I try to do a high cloud sunset to see if there is something to see (like sun pillar and sunvex halos).
this day, we had mosly contrails making here and there some ice halos from my position, but nothing unusual to catch the eye (furtive sundogs, 22° halos, upper tangent and maybe Lowitz buddies but too short in time to be exploitable) (Time-Lapse of part of the day in here, South-South-East Field of View). To find other halos at sunset, the exercice can be tricky, as the global backgroud turn progressivly to yellow then orange so the b-r rendering is more complicated, with adaptation to make in the last 30-45 mins before the end of sunset.
As I don't have automatized this, I find myself resigned to make one setting for the whole sequence to save time in my processings.
And sometimes, something catch my eye, as it did this last 16th of october, last year.
The three next images show 3 differents times of the event, with slightly different processings:
2022-10-16-[17h14à18h58]-NNW-bw-v1-[4-2]-UsM-(49)-5s5-histo-UsM-h20-h28?-h35
2022-10-16-[17h14à18h58]-NNW-bw-v2-[4-2]-UsM-(47)-7s7-UsM-histo
2022-10-16-[17h14à18h58]-NNW-bw-v2-[4-2]-UsM(56)-6s6-UsM-h28?-histo
If needed, I can provide the bw sequence, so you can see (as I do with VirtuaDub) the evolution of the display and distinguish the 28° halo with dynamic (back and forth) play on the sequence.
A sequence you will be able to see there (Version1 & Version2), but with the compression due to GoogleVideo. Again, all raw images are still in my possession, as I guess I might not be done with this display yet.
this day, we had mosly contrails making here and there some ice halos from my position, but nothing unusual to catch the eye (furtive sundogs, 22° halos, upper tangent and maybe Lowitz buddies but too short in time to be exploitable) (Time-Lapse of part of the day in here, South-South-East Field of View). To find other halos at sunset, the exercice can be tricky, as the global backgroud turn progressivly to yellow then orange so the b-r rendering is more complicated, with adaptation to make in the last 30-45 mins before the end of sunset.
As I don't have automatized this, I find myself resigned to make one setting for the whole sequence to save time in my processings.
And sometimes, something catch my eye, as it did this last 16th of october, last year.
The three next images show 3 differents times of the event, with slightly different processings:
If needed, I can provide the bw sequence, so you can see (as I do with VirtuaDub) the evolution of the display and distinguish the 28° halo with dynamic (back and forth) play on the sequence.
A sequence you will be able to see there (Version1 & Version2), but with the compression due to GoogleVideo. Again, all raw images are still in my possession, as I guess I might not be done with this display yet.
Thursday, 28 January 2021
A clear 28° halo on snow surface
Sunshine has been a rare phenomenon in Finland this winter. On 16th January, the sky was finally clear and temperature had dropped to -25°C, so I headed to a nearby lakeshore to observe possible surface halos. There were indeed 22° and 46° halos visible on the snow, so I took a set of 335 photos by moving back and forth of a 50 m stretch of a road along the lake. The mirrored stack revealed that this was an odd radius display with 18°, 20°, 23° and 24° halos present. An interesting feature was that 22° and 23° halos were equally strong and well defined in the stack.
Two days later I got another chance to photograph surface halos in the same place. The temperature was -8°C. Only a modest 22° halo with some bright glints outside it were visible to naked eye, so I did not expect much from the stack. Nevertheless, I took 147 photos. This time the mirrored stack looked even better than two days ago: a strong 22° halo accompanied by several odd radius halos, including a clear 28° ring.
A comparison with the previous display (limited by blue frame in the photograph below) provided another surprise: the prominent ”22° halo” was in fact a 23° halo and 22° halo was missing. So this was an odd radius display with 18°, 20°, 23°, 24°, 28°, 35° and 46° halos. Although there are not many observations of 28° halo on surface yet, it seems probable that it is not as rare as has been thought. This gives some hope that a crystal sample can be obtained one day.
The strong 23° halo and the absence of 22° halo in this surface display is interesting. It means that the usual ”22° halo” on snow may in some rare instances be something else than it looks, but it is not easy to detect such cases from the abundance of common 22° halos. For example, the first observation of surface 28° halo on 7 April 2012 by Jari Luomanen and Marko Riikonen looks rather similar as the current one, and it may perhaps contain 23° halo instead of 22° halo (yellow frame below, photo Jari Luomanen). Although all photos in this collage were taken with Samyang 8 mm fisheye lens, the result should be viewed with caution due to the robust alignment.
Monday, 1 June 2020
Odd radius display at low sun in Berkshire, UK
11-frame stack at sun elevation 2°: unsharp mask and colour enhancement (top), and background subtraction + blue-minus-red colour subtraction (bottom; the latter by Nicolas Lefaudeux).
In the evening of 24th May 2020, a notable display of odd-radius halos and their associated plate arcs occurred in Berkshire, UK. I first noticed faint traces of circular halos - 20° and 23° as I could later confirm from photos - at around 19:20 BST, when the sun was at 13° elevation. Less than 30 minutes later the sun had come down to 9° and first signs of the upper 20° plate arc appeared, making obvious the need to find a view down to the horizon. The display got weaker after some time but regained some intensity less than 30 minutes before the sunset. Unfortunately there were some lower-level cloud interfering with my view for most of the observing time.
Stacked and further processed images from the first stages of the display (below) reveal 18°, 20°, 23°, and 35° circular halos in addition to the aforementioned 20° plate arc. At the end of the display (above), the circular halos are less clear, but plate arcs at 20° and 35° show up better. Most interestingly, perhaps, there are suggestions of 28° circular halo and the associated plate arc at the upper left-hand side at solar elevations 7° and 2°. Previously 28° arcs have been reported in the Lascar display of 1997 and in a few more recent occasions in China, but possibly never before in Europe.
50-frame stacks at sun elevation 9° (top) and 7° (bottom): Background subtraction (left) and background subtraction + blue-minus-red colour subtraction (right).
Tuesday, 27 August 2019
28° arcs from Yunnan, China
Two rounds of week-long odd-radii outbreaks swept across southern China in July and August. The second outbreak turned out to be the more noteworthy one, involving predominantly Chengdu-like low sun plate displays ( http://www.thehalovault.blogspot.com/2018/10/time-machine-chengdu-display-from-july.html ).
Zhong Zhenyu, a member of the Chinese skywatcher community chat group, went halo hunting with his DSLR on August 21 after being informed of the on-going outbreak in his area. The community's collective effort paid off and Zhong was treated with some great celestial rarities.
Upon first glance, the scene immediately reminds us of the Chengdu display, with 3 colored arcs piling up to the right side of the sun. The arc in the middle possesses the same color separation as the other two, especially when USM is applied.
B-R analysis later carried out by Nicolas Lefaudeux further confirms the arc's authenticity. The left-side component also shows up in the processed image. At this point it's quite clear that we've got the third confirmed sighting of 28° arcs in China.
Over the past few years, this type of weak, low sun odd radius plate displays occur rather frequently during summer monsoon over southern China. Now with 3 confirmed and 1 possible cases of 28° arcs within 3 years, chances of these plate displays involving exotic arcs may not be as slim as we expected.
Zhong Zhenyu, a member of the Chinese skywatcher community chat group, went halo hunting with his DSLR on August 21 after being informed of the on-going outbreak in his area. The community's collective effort paid off and Zhong was treated with some great celestial rarities.
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| © Zhong Zhenyu, shown with permission. |
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| © Zhong Zhenyu, shown with permission. Unsharp mask applied. |
B-R analysis later carried out by Nicolas Lefaudeux further confirms the arc's authenticity. The left-side component also shows up in the processed image. At this point it's quite clear that we've got the third confirmed sighting of 28° arcs in China.
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| Processed by Nicolas Lefaudeux. |
Over the past few years, this type of weak, low sun odd radius plate displays occur rather frequently during summer monsoon over southern China. Now with 3 confirmed and 1 possible cases of 28° arcs within 3 years, chances of these plate displays involving exotic arcs may not be as slim as we expected.
Jia Hao
Wednesday, 14 November 2018
Possible observation of exotic 28d upper plate arc
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| Upper left and upper right are image processing by N. Lefaudeux. Lower left is my own processing, and lower right the simulation. All versions of processing are based on the background subtraction method, but use different ways of enhancing contrast. Sun elevation is about 36 deg. |
Some time after the publication of the 31 May 2018 display (see previous post), I returned to analyze the photos in order to take a closer look at one suspicious feature. After strong contrast enhancement, one stack showed a brightening in the area just above the upper 23d plate arc as though a halo may be present. At first, we assumed it was an artefact caused by strong enhancement of the 23d plate arc. However, after fine-tuning of the image processing, we have managed to better reveal this feature, and we can say with the enough confidence that this feature is an another exotic halo — an upper 28d plate arc.
For simulating this halo, I have used a poor plate oriented crystals with a triangular habit, which consist only of a lower exotic (2 0 2 3) pyramid. These crystals are also responsible for the 28d halo, the very faint parts of which you can try to see diagonally upwards from the sun on colored photos above. I have used a triangular habit instead a hexagonal one to remove a 13d halo, which is absent in the observation. In the table below you can find all the crystal populations used in the simulation, and also their some parameters. For ease of comparison, the simulation is placed in the photo scene. It moves into alignment with the photo, as far as field distortion (and other geometric imperfections of the resulting image) allows. As always, the simulation was made with the aid of Jukka Ruoskanen's HaloPoint 2.0. According to the photo, it seems there is faint 18d plate arcs just above 19d plate arcs. If that is the case, this feature makes the display even more similar to the Lascar one (on correspond sun elevations, of course). In order to display this feature in the simulation, regular pyramid crystals in a poor plate orientation were used. But mostly these crystals contribute to 18 and 23d halos. The crystals do not have any prismatic faces because 9 and 24d halos are not present in the display. Based on appearance of the 28d plate arc, the responsible crystals were rather small. Unfortunately, HaloPoint does not allow to change size of crystals, therefore, it is not possible to display the fuzziness of the arc.
Thursday, 18 October 2018
New case of exotic 19d plate arcs
When I first noticed the display at 08-10 local time on 31 May 2018, it was already well-developed. The high cloud layer was very thin and it was visible only in the area close to the sun. At first the display consisted of an upper 23d plate arc and an upper quarter of a 23d halo. A little later I noticed arcs as light spots in the side area of the sun, that reminded me lower 24d plate arcs.
When I processed images, I noticed that these arcs are more like 18d plate arcs than lower 24d plate arcs. But during the observation I distinctly saw that the arcs were located at an elevation lower than the sun, while 18d plate arcs are always located at the same elevation as the sun. I applied stronger processing and revealed a gap between the arcs and a 18d halo. As a result, it became clear that the arcs are exotic 19d plate arcs that were first observed during the legendary Lascar display. In addition, a trace of exotic 28d halo was also revealed.
Some analysis
The halos, known as Lascar halos, are caused by exotic pyramidal crystals with pyramidal faces of (2 0 2 3) Miller index. These exotic pyramids have a 39.1 apex angle while pyramids from regular pyramidal crystals have a 56.1 angle. To simulate the display, I used four different crystal populations. Not one of them have basal crystal faces. The first population is plate oriented pyramidal crystals with upper exotic and lower regular pyramidal faces. This population makes most visible features of the display (19d and 23d plate arcs). The second population consists of crystals with regular upper and lower pyramids, and it contributes to 18d and 23d halos. The population is poorly oriented, in order to reproduce some features of 18d and 23d halos. The third population contains plate oriented regular pyramidal crystals consisting only of lower pyramidal faces. It needs only to enhance the upper 23d plate arc. Finally, the fourth population is added to reproduce the 28d halo. Its crystals is randomly oriented and consists of upper exotic pyramidal faces in triangular habit. That is, the crystals are almost regular tetrahedrons.
The result shows quite good agreement with the observation, except for an exotic lower 3d plate arc. There are two possible reasons for it. The first is that a glow around the sun has much more intensity than halos presented here. It does not allow to reveal a 3d arc, unlike the Lascar display, whose observing place was located at an altitude more than of 4000 m above sea level. At this altitude the atmosphere has a low level of aerosols, and therefore the glow around the sun is very small, and the sky background is dark. My observation point was in Pskov Oblast, which has a flat topography with usual atmospheric conditions. The second reason is that exotic crystals may have triangular, but not hexagonal habit. The 3d arc disappears when triangular exotic crystals are applied.
References
- Nicolas A. Lefaudeux, "Crystals of hexagonal ice with (2 0 2 3) Miller index faces explain exotic arcs in the Lascar halo display"
- Nicolas A. Lefaudeux (personal communication, 2018)
When I processed images, I noticed that these arcs are more like 18d plate arcs than lower 24d plate arcs. But during the observation I distinctly saw that the arcs were located at an elevation lower than the sun, while 18d plate arcs are always located at the same elevation as the sun. I applied stronger processing and revealed a gap between the arcs and a 18d halo. As a result, it became clear that the arcs are exotic 19d plate arcs that were first observed during the legendary Lascar display. In addition, a trace of exotic 28d halo was also revealed.
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| Sun elevation is about 36 degrees |
Some analysis
The halos, known as Lascar halos, are caused by exotic pyramidal crystals with pyramidal faces of (2 0 2 3) Miller index. These exotic pyramids have a 39.1 apex angle while pyramids from regular pyramidal crystals have a 56.1 angle. To simulate the display, I used four different crystal populations. Not one of them have basal crystal faces. The first population is plate oriented pyramidal crystals with upper exotic and lower regular pyramidal faces. This population makes most visible features of the display (19d and 23d plate arcs). The second population consists of crystals with regular upper and lower pyramids, and it contributes to 18d and 23d halos. The population is poorly oriented, in order to reproduce some features of 18d and 23d halos. The third population contains plate oriented regular pyramidal crystals consisting only of lower pyramidal faces. It needs only to enhance the upper 23d plate arc. Finally, the fourth population is added to reproduce the 28d halo. Its crystals is randomly oriented and consists of upper exotic pyramidal faces in triangular habit. That is, the crystals are almost regular tetrahedrons.
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My attempt to simulate the display.
Software: HaloPoint 2.0 by Jukka Ruoskanen
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References
- Nicolas A. Lefaudeux, "Crystals of hexagonal ice with (2 0 2 3) Miller index faces explain exotic arcs in the Lascar halo display"
- Nicolas A. Lefaudeux (personal communication, 2018)
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