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Complex Sun Halo Phenomena During Lock Down - Sundogs, UTA, CZA, Supralateral Arc, Circumscribed Halo, 8 Degree Halo & 360 Degree Parhelic Circle - April 22nd & 23rd 2020

I'm in the midst of lock down in N. Ireland during the Covid-19 pandemic, is it week four or week six?, I honestly don't know any more, at the moment the name of the day has little meaning, Tuesday is the same as a Saturday and Saturday is the same as Wednesday, referring to days is meaningless at the moment. So how have I been coping with this lock down situation?, I will admit I'm seriously missing my nature fix, my trips to the coast, and my night shoots from truly dark locations, I also miss flying my drone, I actually think my Mavic 2 Pro isn't speaking to me anymore but he will get out in due course when the time is rite.

To be entirely honest I've been very busy and I have never once been bored, I'm the kind of person who always has something to do and I also enjoy peace and time to myself so I'm coping rather well, in fact, the days are going in fast. I've been doing what I can from home and I've been helping Roisin work from home too so we have been busy every single day and evening. Between essential work related business I've been walking, filming vlogs for my youtube channel, reading and have been heavily involved with telescopic visual observations of the sky. For the last two weeks we have been treated to some of the finest weather we have had in N. Ireland for a very long time thanks to pro-longed high pressure which brought day after day of blue skies and bright sunshine. By day I worked in the back garden getting vitamin D while listening to podcasts on youtube about astronomy, comets, and even lectures by Dr. Carl Sagan and old recorded radio shows by James Whale. I observed planet Venus every day and made a point of tracking it down with the naked eye in broad daylight without any optical aid, in fact, this became my daily routine - breakfast, open back door, let eyes adjust to the sky, block sun with hand then scan sky 40-46 degrees to the east of the sun and bingo, there was Venus as an obvious pearl-white ball suspended against a blue sky, a planet in broad daylight, always a thrill to do.

It has been so much easier getting through lock down when you have remarkable weather like this to enjoy, it keeps your morale high and sitting out in the garden is the next best thing to being at the coast. Roisin and I have made our fair share of BBQs (no red meat for us anymore) so we have been eating Chicken on skewers with peppers and vegetables which have been delicious. Every night has been clear, in fact, this period has seen the best run of clear nights I've experienced for many years, I couldn't believe how lucky we have been, the timing couldn't have been better. My Meade 8" S. Cassegrain got a clean then every night I hunted down three bright comets - C/2019 Y1 ATLAS, C/2019 Y4 ATLAS (breaking apart) and C/2017 T2 PanSTARRS. Each night I tracked these comets as they moved among the background stars, some as fuzz balls and some with straight ion tails, making note of the comet's degree of condensation, magnitude, coma diameter and shape and colour, it was, and still is, a very rewarding time. I also observed deep sky objects every night from the Messier and NGC catalogues with particular attention spent on galaxies M81 and M82, observing to 03.00-04.00 every night was time well spent getting reacquainted with the sky, in fact, it was perhaps exactly what I needed. I had a chance to slow down, relax, think and enjoy everything that was precious around me, it seemed like my connection with nature was getting closer to me. In the middle of the night with my eye at the eyepiece gone was the sound of late night traffic, instead all I heard was silence with the random call from a Sheep or Cow stirring at night, these sounds were wonderful and brought me back to my earlier observing sessions during the early 2000 period when all I heard at night was the sounds of nature, I felt centered and at equilibrium once again. The following morning I would write up my observations and sketches in my log book then get back to work helping out Roisin or sorting out my own affairs online then back out under the sun once more, I couldn't complain, I was certainly making the most of this situation.

April 22nd 2020

Another gorgeous sunny day, I opened the back door and let the scent of April flowers and trees enter the house, it looked to be yet another gorgeous day. I poured myself a bowl of granola and oat milk for breakfast and scanned through twitter as I ate. I was seeing reports and images of a nice sun halo display captured from many places across Ireland and N. Ireland, the show looked decent too, then complex displays began to appear over Cork and Dublin then N. Ireland, it was these which got my attention, I finished up what I was doing and headed out into the back garden for a look. A prominent 22 degree sun halo was visible over Cookstown, it looked promising and over the course of 20 min's of observation I noticed the halo getting better defined with new forms appearing, I reckoned with a little patience this had the potential to develop into a good display. So I worked outside and kept an eye on it constantly from late morning to early afternoon while monitoring reports on social media.

I decided to dedicate all my time to the halo now, I filmed a vlog from the garden describing what I was seeing then by mid afternoon it had evolved into a stunning show, I had the cameras ready. I was frantically walking around the front and side garden trying to get a decent image but it was very difficult with houses in the area, there was little I could do about my foreground so I accepted what I had and made use of the trees and bushes in the garden. This was 10mm wide angle with 22 degree halo, the bright patches on either side are sundogs (parhelia) and extending beyond those is a curving white streak known as a parhelic circle. On top of the halo was a striking upper tangent arc (UTA) which had vivid yellow and white colours to the naked eye with pronounced 'wings' on either side. On top of the UTA is a white arc bridging the gap between both wings known as a parry arc, I also suspected portions of a circumscribed halo.

10mm lens tilted vertical from the garden, full display but above is a patch of colour called a circumzenithal arc (CZA) often known as an upside down rainbow or smiling rainbow. As its name suggests this arc is located near the zenith (overhead), they are not that common and many people miss them because of their great height in the sky, if you ever see a good halo or other optics then instinctively look overhead as a CZA may be waiting to surprise you. Extending from the CZA is another halo which I will mention shortly, there might also be a subtle pillar extending north of the sun, getting all these forms falls into the category of a complex halo display and to get them all in you really do need a wide angle lens.

Framing the halo with the trees, the UTA and parry arc are clearly visible, my favourite UTAs always have this winged appearance, the more common UTA is often an enhancement to the halo or a coloured patch or linear form, however getting the graceful curve shape extending beyond the radius of the 22 degree halo is always a special treat. UTAs are fascinating because their shape changes depending on the altitude of the sun, their wings open then close like that of a butterfly, as the sun gets lower the wings fold inward and blend in with the halo, when fully open they can take on a very striking wing or even V shaped form and can sometimes meet another halo surrounding the 22 degree halo so the observer sees two halos in proximity to one another or even superimposed on each other called a circumscribed halo.

By late afternoon the halo complex was a spectacular sight with well defined structures, I was shooting time lapse from the front garden while shooting stills with the 5D Mark IV and my older back up 600D with 18mm lens. We have this cool light stand in the garden in the form of three lanterns which always remind me of a scene from Charles Dickon's 'A Christmas Carol' so I thought I would use them for this shot. The sundogs are brighter and the parhelic circle had become brighter and longer. Shooting time lapse was a little different from what I normally do as I usually shoot one image per second when documenting storms and convection, however because there were no low or mid level clouds moving there was less motion to show other than the changing position of the sun and intensity of the arcs so I instead took one image every four seconds.

Annotated version with the 10mm lens on the crop sensor. I actually have two Canon 600Ds, one of which is a back up camera which I hadn't used for some time so I decided to use it today with the 18mm kit lens, I ended up getting fantastic images filling the frame with the UTA and wings, I knew by looking at the LCD screen that they were keepers but the sun was shinning bright on the screen and I couldn't tell for sure until I was back inside.


By late afternoon I had an essential trip to do into Cookstown for supplies, I brought along the 600D with 10mm just in case, I snapped this shot when I briefly stopped using a lamp post to block the sun. Can you name all the forms now?, note how the sundogs are not on the 22 degree halo, they are positioned beyond, this is an indication of the presence of a circumscribed halo which you can see as a ghostly white halo extending upward from the sundogs and joining the wings of the UTA. There's also a 8 degree halo inside the main halo, its subtle but it's in there and seemed to come and go during the day, you can also see it on the video in my vlog, thanks to Noel Keating for pointing this one out as I had missed it at the time, I didn't notice it visually due to the bright hazy sunshine affecting my eyes.

I reached my destination at TESCOs car park, a rare chance to get some foreground interest, I just lifted the DSLR out from the boot and snapped two images and put the camera back again, the settings and focus were the same since my time lapse so no time was wasted, 'every little helps'. When I got back to the house I checked the close up UTA images from the older 600D, the scenes were great, except, the images were ruined by dust on my sensor, I never knew it had been so bad and with the aperture stopped down it made it worse so I had to bin them all, but at least I still had all my wide angle images. Photographing halo displays is easy, you are simply exposing for the scene, you either choose a fast shutter speed or close down your aperture and select your lowest ISO value, usually its a combination of all three to find that sweet spot. Having the aperture closed down is nice because it makes the image sharper and more contrasty and greatly reduces edge of field softness and vignetting, however if you stop down too far it can show up previously unseen dust on the sensor, so always make sure to clean your sensor periodically.

By evening time the display was epic, facebook and twitter were inundated with images, it seemed much of the country was watching this mysterious complex of halos and arcs around the sun, for many it was there first experience of this phenomena which left many in amazement, others wanted to know how they formed and some thought it was connected to decreased air pollution because of lock down, however despite a great improvement indeed with air quality this had nothing to do with sun halos, the halo's presence couldn't have timed itself more perfectly because I feel that many found great interest and contentment from sky watching this day.

Sun halos and their associated phenomena fall within the field of 'Atmospheric Optics' or 'Optics' as hunters call them. They are caused by sunlight bending and refracting through tiny ice crystals within our atmosphere, much like light when it passes through a prism which spreads white light into its component colours. Furthermore the size, distribution, orientation, quality and amount of sides on each crystal will determine what arc or halo will form, so this means that nobody knows for sure what a sky watcher will see during any given display, you can however determine which days might produce an optics display. Since they need ice crystals to form then noting the presence of ice crystal-rich clouds can give you a clue when to be more vigilant, high level clouds such as Cirrus and Cirrostratus often produce the best displays. On this day Ireland was covered in a vast shield of Cirrostratus cloud, this is a high level of hazy milky cloud, at such heights the clouds are far below freezing, often as low as -50 degrees C so ice crystals will be plentiful so you can be fairly sure you might see something, as long as the cloud isn't too dense, its like goldilocks, the ingredients have to be just rite. On other instances halos can form on patches of random Cirrus clouds on days of fine weather and yet other times during unsettled showery days they can also briefly form on the anvils of big convective showers and thunderstorms or on orphan anvils which have become detached from decaying storm cells.

An hour before sunset I went back out, this seemed to be the display which never ended. Using the Canon 5D Mark IV and 15mm lens for the widest view possible showing this full complex display. You can see the CZA at the top centre of frame curving upward into a smile, to give you an idea of how wide this lens is and how much sky is visible that CZA is directly above my head! Also note the coloured larger halo extending away from the CZA, this is a supralateral arc so there are at least seven forms visible and counting the earlier 8 degree halo that makes eight forms. With most halo displays you might see one or two or even three forms at the same time which is quite a treat but seeing all of these together at the same time is much more rare indeed.

Annotated version, I'm hoping this will help readers identify the main structures for future halo spotting, they really are fun to observe and challenging because it really helps to know what to look for in the first place. To increase your chances of seeing a good show, be on the alert for the presence of high level clouds and get in the habit of covering the sun with your hand every day, then scan the sky within the vicinity of the sun, it only takes a few seconds, the view can be even better through sunglasses, in fact, years ago we used to shoot halos through our sunglasses which made for a cool image.

I have seen a number of very good and complex displays over the years, however only once before have I seen a display of this caliber, it was back in 2005 or 2006 when Conor McDonald and I spotted a great display over Maghera, we spent all day taking images and filled up the memory cards with images using our first ever digital cameras, we had the sundogs, 22 degree halo, UTA, CZA and supralateral arc and short parhelic circle, but we couldn't fit them all in our camera frames, there were no 10mm lenses for DSLRs available back then and we were still only using point and shoots, also we didn't have the pronounced wings on the UTA or the parry arc above it, however back then the halo and sundogs and CZA were brighter and had more colour, it's difficult to say which was my best experience, I would be tempted to say this was my best display pound for pound, perhaps because I had it better documented on camera with wide prime lenses. The supralateral arc can be seen extending away from the CZA, there's often much confusion between the more rare 46 degree halo and supralateral arc, both look very similar and located in the same area, however the 46 is separated from the CZA and often has richer colour, the supralateral arc is attached to the CZA, for this reason I suspect this arc to be the latter.

Portrait version at 15mm, wish I had the tripod with me, would have been cool if I had been standing among the grass looking up for scale.

Last image of the day, the parhelic circle extended in length to perhaps 60 degrees long with the naked eye as it jutted out from both the west and east sundogs. I shot time lapses with two DSLRs until the high level cloud disrupted the display, when I stopped shooting I had over 3000 images taken. The perfect end to a wonderful day, admiring such a rare show which lasted all day long while at the same time basking in the heat of the sun, I had completely forgotten we were in lock down, I was thinking within another zone and was loving it, I headed in before sunset to recharge the batteries but little did I know that the stage was set for more action the following day.

April 23rd 2020

I woke up to yet another beautiful day with bright sunshine, it promised to be one of the warmest days of the year so far. I aired the room and ate my breakfast as normal while scanning social media and yet again reports and images were coming in from all over N. Ireland reporting another sun halo, I went out the back for a look, the sky was more hazy today and the Cirrostratus more dense but sure enough there was a vivid halo already well placed in the eastern sky, I decided to keep an eye on it as I set up out in the back garden to help with Roisin's work while listening to Professor Alan Fitzsimmons on youtube talking about sungrazing comets, I would periodically check the sky and monitor the halo which was a good 22 degree form with a vivid yellow-white UTA, the formation seemed to improve by early afternoon so I began to document the scene.

22 degree halo, UTA with wings, faint parhelic circle forming on the west (right) side with hints of a circumscribed halo too. I have a BBQ/fire pit in the backyard which looks like a small circular table so I mounted the 5D Mark IV on that and began filming a vlog then shot a time lapse with the 15mm Blackstone lens.

I was having a quick sneek back on the lap top inside and got a message from astronomer John McConnell, we were chatting about the halo display then John said there was a massive ring above the halo all over the sky, I ran outside and looked up, sure enough it was here too, this was a full circle or 360 degree parhelic circle. I set up a second camera, the 600D with 10mm lens, and began another time lapse, this time with part of the halo and UTA framed with the eastern section of the 360 parhelic circle, I couldn't get the entire structure in, only a fisheye or wide view on a Go Pro or a montage of images merged together would show that effectively. Look at the white spot to the left of the halo, that's the eastern sundog, follow it out into the blue sky to the left, can you see the curving pale white parhelic circle?

Annotated version, this field covers the S and E sky sectors

I had now turned my back to the sun and faced due north towards the anti-solar point, you can see the parhelic circle as a faint loop above the tree

Annotated version, notice there's no CZA today as the elevation of the sun is still too high. The 360 parhelic circle is rather special, today included I have only witnessed this phenomena on four occasions in my life, three around the sun and once around the moon. I recall a vivid 360 arc during a very hot day while in Portballintrae a few years ago and another from Maghera many years earlier. However the most rarest of all the optical phenomena I have seen to date was a 360 degree parhelic circle on a moonlit night when I was doing photography in a field outside Maghera, I was likely doing a meteor patrol at the time and seen it quite by chance. The parhelic arc with wegener arc and 180 parhelia against a backdrop of stars was incredible. One year I also saw a spectacular lunar CZA among a rich star field, this was one of my favourite optics experiences to date, it was stunning and vivid, I didn't have a camera with me and I have never seen one since, however I live in hope of seeing anothe, I have just found the link to the earlier sighting, the lunar version is called a paraselenic circle, check out the report.

Another view of the full circle parhelic circle merging with the 22 degree halo, this was like a ring of smoke against the blue sky in a vast circle which could be traced around the sky where it merged into the sundogs and halo to the south.

Facing due north, the next time you see a halo or sundogs take a moment to block the sun and look overhead for the CZA then turn your back to the sun and scan the sky in the opposite direction and you might just catch one of these complete parhelic arcs.

The parhelic circle vanished as suddenly as it appeared so I completed a time lapse of the halo and turned all the cameras off for a rest, once again approximately 3000 images were taken between the two cameras. Getting treated to such beautiful and complex halo displays for two full days in a row has been an absolute treat, especially with such glorious sunny weather, I got two days of time lapse sequences, still images for the memory, wonderful phenomena witnessed and even got a sun tan in the process which made for a precious memory during April, I'm truly grateful that the sky has been treating us so much during this difficult time, it almost felt like an old friend (nature) was there to help me through this period by making me look up so often and keep me busy.

Vlog covering day one with the complex halo display, this was filmed during the earlier part of the day then ends with a time lapse later in the evening, this is the first time I've ever time lapsed a CZA in my life.

Day two of halo action, VLOG with me chatting about the halo and how they form from the garden, I recall feeling so warm outside which felt fantastic, I couldn't even see the camera screen due to solar glare, I've never been much of a vlogging person however I have been doing more of these recently due to the lock down situation but judging by the emails I'm getting many of you seem to enjoy watching them so I might do more of these in the future.

Time lapse from day two of the 22 degree halo, sundogs, UTA and the large full circle parhelic circle, another time lapse first for me. I have to say I really enjoyed these two days of sky action. Thanks very much for reading and I hope you are all keeping safe and well, and don't forget - keep looking up!


Martin McKenna

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