Monday, 30 May 2022

Stacking comparison: Canon 80D vs. Nikon D7000

by Marko Riikonen and Petri Martikainen

One of us, Martikainen, was passing on May 25 though Joensuu where the other one, Riikonen, was staying, and we had decided to do a stacking comparison with our cameras weather allowing. It went swimmingly. There was high cloud from morning to the sun set and when we rendezvoused in the evening on a grassy field next to lake Pyhäselkä to set up tripods, cameras and blockers for the test, the display reached its peak.

Martikainen was photographing with Nikon D7000, Riikonen with Canon 80D. We both had Samyang 8 mm fisheye, though not the same model. Our blockers differed a bit. Martikainen had the blocker on a separate tripod, whereas Riikonen's was attached to the camera hot shoe.

We set identical iso, shutter speed and aperture. Then we took 136 photos every 5 seconds, at around 1/3 of the of way there was a little longer simultaneous break.

In postprocessing we harmonized the color temp and tint of raw's before turning them into 16 bit tiffs for stacking with Halostack in full size. As the 80D images are larger than D7000, the former's final stack was downsized to match the latter before we gave them identical application of the usual methods of usm, br and bgr.

Downsizing the 80D stack before the enhancements could make it lose some of its higher resolution advantage, so we made a test. Usm with a radius higher relative to the two cameras image size was applied to the 80D stack before downsizing and this was compared to the version where the 80D stack was first downsized and then usmed (with the smaller radius). There was zippo difference. So it seems ok to downsize the 80D images to D7000 scale before enhancements

The test showed D7000 as the better halo camera, something that Riikonen had suspected all along. We do not know how to characterize in proper terms the differences seen in the photo comparisons, but it seems like 80D has more problems with color noise.

Terminology:

usm = unsharp mask
br = blue minus red
gr = green minus red
bgr = background removal 

Original stack. Left 80D, right D7000


 
2 x usm (radius 25, 25)



 
3 x usm (radius 25, 25, 12.5)


 
br


 
br + bgr

gr


 
gr + bgr


 
bgr

100% detail (after D7000). Left D7000, right 80D. 2 x usm (radius 25, 25)

Monday, 16 May 2022

Double CZA, Kraków, Poland


On May 7, I was working on my programming side project. At about 17:15 local time (UTC+2h)
I was finally able to take a short break. I decided to get some fresh air on my balcony (facing south).The temperature was about 17-18°C and a substantial fraction of the visible sky was covered in rather thick clouds. The zenith area, however, was quite clear, except for a layer of nebulous cirrostratus clouds and some broken mid-level clouds. I could see a faint circumzenithal arc, so I went back inside and grabbed my camera. I took only three pictures of the CZA at 17:20, 17:21 and 17:22, before the arc disappeared completely. I noticed it was a little broader than usual, but I thought that maybe it had something to do with the solar altitude. At 18:30, I finished my work for the day and looked out of the window again. The CZA was back and I thought I could see a supralateral arc as well, so I took some more pictures. About 25 minutes later, thick clouds rolled in from the west and obscured the display. 




Since it wasn’t a particularly bright display, I didn’t think about it much until the next day when I began processing the photos I took over the last week. I was pleased to find CZA, supralateral and a suncave Parry arc (Apr 30) and another CZA + supralateral display (May 6), and then began to process the few photos that I’d taken on the previous day. The first one showed just a normal CZA, but in the second one I could see a faint rainbow smudge right under the CZA. At first, two things came to my mind: 46° halo and camera artifacts. Stellarium told me that the sun altitude was 25°. According to a chart I found on the internet, at this solar altitude the CZA should be quite narrow and the 46° halo should touch the CZA. Also, the arc in my pictures followed the shape of the CZA instead of curving downwards. I could see it in the third picture (taken in a slightly different direction) too, so I thought I could safely assume it was not an artifact or a lens flare. The rest of the photos I took later in the evening revealed a regular CZA, supralateral arc and a 46° halo – they looked completely different to the weird double arc. Then I remembered reading about an unusual type of halo related to the CZA before, but I couldn’t remember where, so I submitted my report to spaceweather.com in hope of it getting some attention there.

Meanwhile, I went on looking for the mysterious CZA phenomenon I read about earlier. I stumbled upon it a few days later, by accident. Someone had posted a link to a Halo Vault article on reddit describing a secondary CZA spotted in China. Then I found the report of A.F. Jensen. I was really excited when I realized that the second report fitted my observation quite well, so I decided to write you immediately. 

Lately, halos have been keeping my quite busy. I could see another CZA / supralateral / suncave Parry arc combo in the morning of May 14 and there is a nice 22° halo visible right now. Honestly, I can’t remember seeing that many displays in a row since I’ve seen my first one in May 2005!

                                                                                                                                         - Tomasz Adam

Sunday, 13 February 2022

Peculiar Elliptical Halo in Suzhou, China

On Feb 5 a very strange case of elliptical halo was recorded by FU Lei from Suzhou, Anhui Province, China.




The short-lived elliptical halo in the display was sliced by the cloud bands into two segments, both exhibit a gradual increase in radius as the halo approaches the cloud bands' lower limits. Such behavior shall be explained by varying apex angles of responsible flat pyramidal crystals.


According to halo experts Marko Riikonen and Nicolas Lefaudeux, it's been long debated whether there's a 'preferred' apex angle in the elliptical halo theory. This particular case serves as strong evidence that there's probably no 'preferred' angle at all. Ellipses can sometimes behave like iridescent clouds - instead of a smooth water droplet size gradient, there is a gradient of crystal angle.

Jia Hao

Sunday, 16 January 2022

(Almost) Solitary Parhelic Circle in Genhe, China

On Jan 8 WANG Jingxian from Genhe, China captured a very interesting diamond dust display in which the only prominent halo was a (almost) solitary parhelic circle.




According to WANG, the display had already passed its prime when the pictures were taken and the parhelic circle had faded somewhat. Except for a diffuse pillar and very weak parhelia, nothing else showed up throughout the display - no circumzenithal arc, no 120° parhelia, no upper tangent arc.

Solitary parhelic circle has been observed before in China, but not at such low solar altitude. Marko Riikonen later reminded us of a very nice photographically confirmed case by Jarmo Moilanen back in 2004. (hopefully Jarmo can visit this page and share his capture in the comments). Marko himself also witnessed a streetlight display in Oulu back in 2002 ( https://www.ursa.fi/ursa/viestinta/listat/halo-l/0543.html ) in which the parhelic circle and circumzenithal arc shined without parhelia.

Crystal samples from such displays are still much needed to pinpoint responsible crystals. Marko noted he saw stellar plates were falling on his sleeves during the Oulu display, and suggests such stellar shapes could theoretically be the cause of the absence of parhelia.  In the Genhe display where even the circumzenithal arc is missing, the crystals probably need to be more optically subpar, allowing only external reflections on vertical faces. Besides, as both Marko and JI Yun suggest, optically imperfect columns could also play a part.


Jia Hao

Sunday, 19 December 2021

First Halo Taken From Martian Surface By The NASA Mars Perseverance Rover, 15th December 2021

On the 15th December 2021, history was made when the Mars Perseverance Rover photographed the very first halo from the surface of Mars. The three images shown below are from a set taken from image series Sol 292 available on the NASA Perseverance Rover website,

https://mars.nasa.gov/mars2020/multimedia/raw-images/

Whilst technically it is not the first Martian halo, that accolade having been given to a subsun photographed from orbit by the Mars Global Surveyor satellite in January 2006, it is the very first to be taken from the surface of a planet other than Earth.



So what kind of halo are we looking at?  In the Martian atmosphere, both water and CO2 ice crystals are present. Taking the wide angle distortion of the Navcam lens into consideration, space artist Donald E. Davis who first noticed the halo in the Perseverance image archive wrote on Twitter that it "appears roughly consistent with a 22.5 degree radius". In all likelihood, the halo formed in water ice clouds rather than CO2; if the halo had been formed by CO2 crystals, then the radius would have been larger than what we observe. Likewise, we also have brightenings on opposite sides of the halo which are probably consistent with diffuse tangent arcs.

Image processed by Nicolas Lefaudeux.

Donald Davies has done some truly excellent work recreating the full halo from the separate images and has even produced a superb all sky reconstruction which has all the hallmarks of becoming iconic. You can find his ground-breaking work on Twitter here:

Image processed and manipulated by Donald E Davis.

Image processed and manipulated by Donald E Davis.

We sincerely hope that this will be the first of many Martian halos that will be captured by the Perseverance Rover and that this will open up a whole new field in halo science.

Major Update - 28th December 2021

Since posting the news about the discovery of the first Martian halo, Nicolas Lefaudeux returned to the Mars Rover archive to see whether he could identify further previously unrecorded halos. The results of his search are staggering. Besides the initial ground breaking Sol 292, he has discovered a further seven Martian halos of varying quality and intensity. These are Sol 145, 193, 249, 285, 289, 290 and 303. These confirm that both Sol 292 was not an isolated event and also that halos on Mars are a relatively common occurrence. All images presented below processed by Nicolas.

Sol 145

Sol 193

Sol 249

Sol 285

Sol 289

Sol 290

Sol 303

Sol 303

Tuesday, 30 November 2021

Two Displays in Åre, Sweden 8th & 14th November 2021

We present a guest post by Minna Kinnunen showcasing two really nice displays she was fortunate enough to observe at the ski resort in Åre, Sweden. 

First display – 8 November 2021

The weather forecast promised a few degrees freezing and blue skies, but the only problem was that when I looked out the window in the morning, it was most definitely overcast with the clouds hanging low. Then it dawned on me that this could well depend on the altitude and/or the snow cannons working at full (with Åre being the biggest skiing resort in Sweden), and my experience in these conditions is that if I make my way up the mountain, the blue sky will appear. 

The circumzenithal arc was beautiful but the only way I could capture it with my 24mm lens was to take two horizontal photos and stitch them together in Photoshop to show the whole thing. Parhelia are strong, upper tangent arc and sunvex Parry are a bit fuzzy and there's even a faint Moilanen arc.

I drove to Ullådalen just outside Åre and sure enough, I saw some pale blue sky above me as I parked even though the landscape otherwise was still shrouded in fog/ice crystals. Early on in my hike I saw the halo, just a ring around the sun but exciting nonetheless! 

At this point the halo was at its absolute best, a very distinct display. Really a pity I couldn't capture it in its entirety with my 24mm lens.

The further out I got, the thinner the diamond dust and the clearer the halo. And then it wasn’t just the ring around the sun, it was another ring around the sun and it was a ring across the entire sky and it was pillars and it was arcs, quite simply the most stunning halo display I had ever seen. I really had no idea what I was looking at beyond “a halo” but I knew it was special for sure so I tried to shoot it the best I could, considering that I only had a 24-105 mm lens with me and 24 mm was barely enough to contain the 22° halo. 

All I could do was to attempt to capture the details. The pillar from the parhelion is very strong here, is it a Schulthess or Lowitz arc or something else?

Later in the afternoon but well before actual sunset the sun disappeared behind the mountain, but as a parting gift it gave me a beautiful display of upper and lower pillar, upper tangent arc and Parry sunvex. 

As the sun started to disappear behind the mountain, the upper tangent arc and Parry arc became clear. Even the helic arc is still visible.

Since I didn't know much about halos at this point, I thought the white pillar 120° from the sun was actually part of a fogbow. As I already have some nice pictures of fogbows, I didn't  shoot it until the very end as an afterthought when it had alsmost disappeared. The full 360° parhelic circle had been visible earlier.

I learned those names afterwards as I was studying my pictures and I also thought I identified the 46° halo, but it’s probably a supralateral arc? My biggest question mark however is the pillar going down from the parhelion, I am calling it “bisolpelare” in Swedish which is a direct translation of sun dog pillar, but maybe we’re really talking about a Schulthess or Lowitz arc? 

I got out of the mountain's shadow for a brief moment, the parhelion and parhelic circle are still very strong.

I made a short film on the trip https://youtu.be/PRT3Lf_WPFM, the footage gives more information than my still pictures. I made an attempt at naming all the halo components, I realise now that I’m probably wrong about a couple of them so I will need to update the video! 

Gear: 
- Sony A7C + 24-105/4
- Pictures are taken between 10.33 and 14.23 
- Sun at 8.52 degrees for the first picture and 4.74 for the last, 9.96 degrees at transit 
- Altitude for shown pictures 730-800 meters 

Second halo – 14 November 2021

This is the second halo as I started going up the piste. Amazing upper tangent arc and sunvex Parry with a fairly distinct suncave Parry. The supralateral arc is more colourful now than the last time.

Less than a week later the weather forecast once again promised cold weather and sunshine. Of course, I had to go back to Ullådalen to see if the proverbial lightning indeed strikes twice, but as I parked my car it didn’t look quite so good. I did see a stunning upper tangent arc and Parry arc though and now I actually knew what they were, having read about halos all week. 

A little bit higher up the diamond dust is very thin and just about all that remains are the spectacular arcs above the sun.

This time I went to the opposite direction from the earlier trip, up the piste towards the small peak of Rödkullen at the foot of the mountain of Åreskutan. The diamond dust that wasn’t very thick to begin with got thinner with every step and the halo faded with it. Up on Rödkullen the only hint of anything exciting going on was the rainbow colours I saw on the mountain side opposite the sun. 

The irridescent (?) fog opposite the sun.

Back by the car the halo became visible again. Since I now had a better idea of the halo types, I had a look around to see if I could find anything that I haven’t already seen. It didn’t look that good though so I figured that the show was over, time to go home. However, as I was driving down the road and the diamond dust got thicker, the halo made a glorious comeback. I tried to find some nice spots to shoot it, got too far down on the road and turned back. 

Going back up with the sun on my back, I saw it – the anthelion! I could barely contain myself, just jumped out of the car and shot it right there in the middle of the road. Which was just as well, because the anthelion turned out to be very short-lived, it only took a few minutes and it was all gone. 

What an unexpected and welcome sight, the anthelion and anthelic arc!

I drove the road up and down twice more without discovering anything new. Down the road the diamond dust was too thick and up it was too thin, the line in between was quite sharp. 

On my way home though I saw the halo by the Åresjön lake, so I took one more shot of the halo to cap off an absolutely amazing week of halos. 

On the opposite side of the anthelion, this halo.

The larger ring – be it 46° halo or supralateral arc – is white in the first halo but coloured in the second. Is it the same thing or a different type? 

Even a Tape arc made an appearance.

Gear: 
- Sony A6300 + 10-18/4 (15-27 mm effective) 
- Pictures are taken between 10.07 and 13.37 
- Sun at 5.86 degrees for the first picture and 5.81 for the last, 8.33 degrees at transit 
- Altitude for shown pictures 665-785 m. 

//Minna Kinnunen – vandrafotaleva.nu 

Update - 10th December 2021

When Minna's post was originally published, I was working on the assumption that we were dealing with a 120 pillar. However, after processing the image in several different ways, I noticed something unusual on either side of the pillar. I was fairly sure that the feature was real and not an artefact so I reached out to the halo community for suggestions as to what it might be.

'Mikkilä's soul'

Almost immediately Marko Riikonen recognised it for what it was, 'Mikkilä's soul' or Mikkilä's diffraction pillar. More details here,

https://www.atoptics.co.uk/fz742.htm

https://www.taivaanvahti.fi/observations/show/46324

Marko commented that whilst the diffraction pillar occurs reasonably frequently in spotlight displays, to the best of his knowledge, this is only the second time it has been observed in a solar display, the first being in Sotkamo, 2015. Minna checked her Photographers Ephemeris and further confirmed that the pillar was indeed located at the anthelic point.

Position of diffraction pillar as shown on Photographer's Ephemeris

Final irrefutable confirmation was provided by Nicholas Lefaudeux who has very kindly processed the image and managed to bring out the delicate coloured fringing of the phenomenon.

Processing by Nicolas Lefaudeux

As an amusing aside, when Minna was shooting the display, she didn't realise what the 'halo' she was seeing was and only took one photograph of it. Later during the editing process, she wasn't too impressed with the image and actually deleted it! However, on further reflection she rescued it from the trash and in so doing joined a very select club!


Alec Jones

Monday, 14 June 2021

Major Halo Outbreak in Southern China, Apr 29 ~ May 01, 2021

A major halo outbreak stunned sky enthusiasts in multiple Southern China provinces between Apr 29 and May 01, with a surprisingly wide variety of high cloud halos. Even though nothing particularly rare were discovered, it's still worth sharing some of the highlights as eye candies to the international community. 

(We were completely overwhelmed by the huge number of online records and submissions during the outbreak. Special thanks goes to JI Yun, who spent days going through thousands of cases and identifying the noteworthy ones. All photos in the post are shown with permission. Minimal post processing applied.)


Mid-to-high Sun Parry Arcs


Likely China's best mid-sun parry arc record to date, taken by PENG Lijuan in Hunan Province on Apr 30. 

Taken by JIANG Simin in Hunan Province on Apr 30. Note how the lower suncave parry arc becomes a full circle under the 70° high sun, and cuts right through the parhelic circle and Wegener arc. What a sight to behold. 

Helic Arc

Helic arc has been extremely rare in China, both in high clouds and diamond dust. The previous two high cloud cases were forgettable at best - barely visible in heavily processed raw images.

Finally during this outbreak, some good quality high cloud helic arcs were photographed, with mobile phones!

Taken by PENG Lijuan in Hunan province on Apr 30. There seems to be traces of lower Lowitz arc tangent to the left side of 22° halo too.

Taken by JIANG Simin in Hunan province on Apr 30.


Odd Radius Column Arcs


Taken by ZHANG Yifei in Sichuan province on May 1. 9°, 20°, 24° and 35° column arcs are all sharp and vivid. Note how the 20° and 35° column arcs differ from their random counterparts by being half circles.

Taken by LIANG Yongqiang in Guizhou province on May 1. Column arcs in this one are not as intense as the Sichuan photo. However, look carefully for the 35° column arc which cuts through a weak Wegener arc inside the parhelic circle. Such combo doesn't come easy!


Airborne Odd Radius Plate Arcs

Upper 20° and 35° plate arcs are very common during summer months in Southern China. Their lower counterparts, on the other hand, are far less frequent. In fact, the number of sightings we logged before this outbreak is zero. The void is now filled, finally.

Taken by BAC onboard a Zhuhai - Shanghai flight, on May 1. 9°, 20° and 35° lower plate arcs dominate the show. 24° lower plate arcs are probably there too, as well as weak 9°, 20° and 35° column arcs.

JI Yun & JIA Hao