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(Above) C/2025 A5 Lemmon Sep 29th by Alessandro Carrozzi from UT, USA
It's October, the nights are drawing in, there's a definite nip in the air, and the leaves are falling from the trees. As Autumnal starry nights beckon us out with our telescopes we might just have something extra special to see in the night sky this fall. Several comets have been making headlines and two of these might be visible as binocular objects in the evening sky for northern hemisphere observers, however one comet in particular is standing out from the rest - designated C/2025 A6 Lemmon. This comet was discovered earlier in the year and after it's orbit was calculated and light curve plotted Astronomer's predicted the comet would peak at mag +10 this October, in other words a relatively faint telescopic comet not to get too excited about, but interesting to observe all the same.
Then the celestial tables turned, as comet Lemmon emerged from solar glare during the Summer it was observed to be considerably brighter than expected. Further observations ruled out an outburst event, this was an intrinsic brightening of long duration, this was an active comet with a bright future and it soon became clear that it could become a binocular or even faint naked eye object later this year. I observed the comet for several mornings recently with my latest observation on October 4th at mag +6.2, the comet was easy to see in 10x42mm binoculars even with a bright gibbous moon in the sky and very little dark adaption obtained. That's when I knew this comet was going to live up to expectations, had the moon been abscent I felt certain it would have been nearing the threshold for naked eye visibility. The comet was brightening rapidly every night and CCD images have revealed a long and complex ion tail rich in streamers with regular disconnection events as the tail was constantly buffeted by flucuatations in the solar wind.
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(Above) Light curve forecasts based on CCD and visual observations by Bum-Suk Yeom
The comet reaches it's closest approach to Earth in late October and will reach perihelion in early November when it nears the orbit of Mercury, this comet will be feeling the wrath of the sun's heat and will flourish into a moderately bright object. A newly published light curve factoring in both CCD and visual observations shows a bright trend with several possibilities. The comet is expected to reach mag+4 however more optimistic forecasts place Lemmon anywhere between mag +3 and +2. If the comet reaches any of these values then we can expect a naked eye object. For new observers or those with light pollution this could be a faint naked eye or more likely a binocular object. However for experienced comet observers with dark skies Lemmon might actually be a fairly obvious naked eye sight for anyone who knows the sky intimately.
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(Above) C/2025 A6 Lemmon finder chart by Greg Miller of Louisville Astronomical Society
So where can I find comet Lemmon? as I write this on October 6th the comet is visible in the early morning sky near the eastern paws of The Great Bear (Ursa Major), however the moon is also full making this the worst time to see it, this is only a minor blip as the viewing geometry will improve. The comet continues moving eastward and in a few days will become circumpolar (visible for much of the night) and will be best seen as an evening object from October 10th onwards. The good news is that the moon will be waning each night and I estimate that in a week or so the moon will have moved sufficiently away to suddenly plunge the evening sky into darkness, this dark window will increase in length each night as the comet brightens, in fact, the timing could not be better, the comet will achieve maximum brightness over the new moon period at an elongation greater than 40 degrees from the sun in dark skies!
During mid October Lemmon will trek through Canes Venatici making a close pass by mag +2.8 naked eye star Cor Caroli on the 16th. From the 21st the comet can be found within the kite-shaped figure of Bootes the Herdsman to the north of brilliant Arcturus which will serve as an obvious marker to hunt down the comet for new observers. Between the 24th and 25th it was pass to the south of Corona Borealis the Northern Crown, imagine if Blaze Star TCrB erupted then!, what an experience that would be with a naked eye Nova and naked eye comet in the sky at the same time - we can only hope. By the end of the month it will sail through Serpens Caput then into the milky way within Ophiuchus when it will once again be lost in solar glare. All of this takes place in W-NW evening sky at a convenient time for most observers.
1) Keep in mind however that even if Lemmon reaches mag+3 it might not be as easy to see as a star of similar magnitude. The reason is that a star is a point source of light, it's highly concentrated and hence easy to see, while the light of a comet is spread out over a larger area of sky, so that magnitude 3 value could surpass 15 to 20 arc minutes of actual sky reducing its full brigtness. However don't be worrying about this too much as the comet will still be visible to the naked eye.
2) This is also a gas-rich comet. Comets with high concentrations of dust develop tails of a much higher surface brightness, the dust particles do a good job of reflecting sunlight making the comet's tail easier to see. Since Lemmon is gas dominated the tail will be less impressive than it's dust counterparts. A tail will be visible however it might take a little patience and well developed dark adaption to see its full splendor.
3) The internet is full of spectacular images of this comet, however don't expect to see this kind of detail in your telescope. These images are taken by the world's best astrophotographers from very dark locations using state of the art equipment with advanced processing methods to ferret out the intricate details. To the visual observer the comet will look more fuzzy and less distinct, but no less beautiful in it's own way.
Using your binoculars or telescope the comet's head or 'coma' will look like a greyish round fuzzy ball brighter towards the centre, this brightening is called a 'central condensation'. The coma itself upon closer inspection might exhibit a blue-green colour due to gas emissions. The condensation could have a small fuzzy star at centre, this is called the 'false nucleus' as the real icy nucleus can never be seen. The inner coma could also display 'jet's emanating from the condensation.
As we look downwind away from the sun we will be able to follow the comet's tail which should vary in colour from grey-white to blue depending on how active it is and how bright it gets. The tail will likely contain fine streaks or lines called 'streamers' with irregularities and enhancements known as 'knots'. Imagers will likely capture disconnection events when the tail splits in two and a new tail grows back in it's place. Lemmon should be very impressive in telescopes and beautiful in any binoculars and a worthy target for even basic photography. A 100mm telephoto lens or 50mm lens should suffice to capture a record of the visitor to some degree, those with sky trackers will be at a greater advantage. Autumn is also aurora season, due to the comet's interesting position in the NW/W any decent displays which appear could offer a fabulous prospect of getting an image of a comet with auroral beams or band at the same time.
New gas tail simulations by Nicolas Lefaudeux suggest the comet could unfurl a gas tail between 20 degrees and 50 degrees long in deep exposure images...
''During the period between 16th and 27th of October, the magnitude of the comet should increase from magnitude 4 to brighter than magnitude 3, and the tail will be at its longest, probably measuring between 15° and 40° photographically. With a solar elongation around 40°, the conditions will be ideal for very spectacular images of the complex plasma tail of the comet during this period. According to the simulation, the maximum tail length should be around October 20th, with a maximum tail length between 20° and 50° photographically''.
''The surface brightness of the tail should be enough for some part of it to be seen visually from dark skies with binoculars, and possibly to the unaided eye, especially in the late part of the period when the tail’s surface brightness should be the highest. Around this time, it is also possible that some dust tail develops even if the comet is mostly gaseous. If so, it should reach its maximum length in the later part of the highlight, with length possibly up to 10°''
Let's hope for regular clear skies from mid to late October. C/2025 A6 Lemmon won't be a 'great comet' or even a very bright naked eye comet like last years T-Atlas however it should be a faint naked eye object at the very least and something interesting for us all to observe. Comet SWAN will also appear low in the evening twilight during this time, perhaps between mag +6 and +7 so we will have two comets to enjoy within binocular range. Then in November interstellar comet 3i/ATLAS will make an appearance in telescopes so the late half of 2025 is certainly looking to be an interesting time for comet lovers. At least these comets will keep us entertained while we wait on the next great comet to be discovered, I wish all clear skies and happy observing.
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It's early Autumn and already the convective activity across N. Ireland has been more active than anything during the late Summer thanks to low pressure systems bringing continuous fronts and showery troughs. On September 11th we had 800j/kg of CAPE on a SWly flow with -40c cool pool aloft and models indicated the Sperrins could be a good target area. I spent the day there with Colleen Webb however we began to loose hope after battling hours of low cloud and non stop rain. Before 17.00 I was tempted to go home but relocated to Broughderg first when a sudden clearance opened up revealing a strong line of sunlit convection which transformed into a beautiful mature Cumulonimbus dominating the sky
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On September 4th 2025 we had a late season set-up with 500 CAPE on a Wly flow. E parts of NI looked best but my expectations were low due to the absence of strong shear. I met Colleen Webb while crisp updraughts began to develop rapidly which exhibited strong tilting and a vault which was entirely unexpected. We chased one particular cell to Slemish where we got treated to the best storm structure of the year with leaning updraughts, vented precip, a well formed dark base with striation lines with black scud tags swirling and rotating below. Then a dramatic lowering formed at close range rotating into what can only be described as a large wall cloud. The cell in essence took on transient supercell traits against all odds, this was followed by the sighting of an impressive white rope funnel cloud during the drive home. One page report with 25 images and 1 video clip. - REPORT.
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It's late summer, the weather has been exceptionally dry, there's been little in the way of convective activity however there were a few interesting events and memories worth documenting. I got captivated by a surge in Butterflies at Lissan House, a drone day trip to Co. Down documenting harvesting, stone circles and St. John's lighthouse. Then an all night moonlit Perseid meteor shower watch at Lough Fea complimented by a beautiful Venus-Moon conjunction in the pre-dawn sky. Then a potent convective cell which erupted in strong solar heating and 800 CAPE over Moneymore which flooded the town and which sported the most impressive updraughts I've ever seen on a warm topped cell. Finally a warm summer's evening at Myroe on the shores of Lough Foyle filming a combine harvester at work at sunset like a scene straight from 'Dallas'. One page report with 15 images. - REPORT.
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Just when I thought the 2025 season was over nature turned the tables with a major thunderstorm set-up over W Ireland. On July 13th big CAPE, strong wind shear, and deep moisture all converged ahead of a cold front resulting in the biggest outbreak of storms this year. My Wife and I decided to chase and turn the day into a road trip. We visited Mullaghmore, Benbulbin, then reached our target area at Rosse's Point in Co. Sligo. From there we watched an enormous highly sheared multicell storm come into view with solid updraughts and anvil sheared out over the sea producing lightning every second for residents below it, then capturing the storm with Black Rock Lighthouse followed night time lightning over Co. Antrim at 2am. This single day has made my entire storm season. One page report with 27 images and 1 video clip. - REPORT.
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Just when I thought I wouldn't experience another wild fire on the scale of Ballygawley I was proven wrong on April 10th 2025 when I spotted pyrocumulus in the sky which correlated with online reports of a gorse fire in the vicinity of Lough Fea near Corrick Road. I drove up for a look not expecting anything major until I arrived at the scene and got the drone in the air for a better look. I was astonished to witness a massive fire in progress burning trees and bushes with multiple sources covering a very large horizontal extent. The scene was spectacular yet terrible in equal measure while almost 50 fire fighters tackled the blaze to bring it under control. This event was followed by another fire on Glenshane Pass for the next two nights when we made an attempt to film the fire at night with the drone. This marks four wild fires filmed within five days making this one of the most active fire seasons in years. One page report with 17 images and 1 video clip. - REPORT.
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A major outbreak of wild fires has been making the news across N. Ireland with 250 fires within a week, most were deliberate. On April 8th 2025 I had intentions of shooting the sunset when suddenly reports arrived on social media of another major wild fire near Ballygawley. I took the chance and drove to the scene to document the event, the fire was massive and over one mile long and wider than any I had seen before with multiple sources. The wild fire was burning near wind turbines and was rapidly approaching a house forcing owners and their pets to evacuate while 45 fire crew with 29 appliances battled the blaze working all through the night with a fire that was as dramatic as it was dangerous in the light of the setting sun. One page report with 22 images and 1 video clip - REPORT.
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Astronomy is not the only subject I'm interested in, check out my N. Ireland Storm Chasing section and view the chase reports and images which detail not only storms but other phenomena such as a moonbows, noctilucent clouds, aurora displays and exciting nature related photo shoots.
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Martin McKenna
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