…actually, it’s already here, and it’s been here for a while.
Comet-watchers have been getting up at you’re-having-a-laugh o’clock in the morning for the past month or so to observe and image a comet called “C/2025 A6 (Lemmon)”, but now it is becoming visible in the evening sky too, making it much more accessible to many more skywatchers. Of course, this means there’s now an increasing amount of hype and misinformation appearing and being Shared online, with wild predictions being made of how it will “light up the sky” as it reaches its closest point to the Sun and appears at its best in our night sky. So, what’s the real story? What might we actually see at the end of this month and at the beginning of next month?
Before we look ahead, let’s look back, to the beginning of the story…
A6 Lemmon was discovered by astronomer David C. Fuls, working on the Mount Lemmon Survey, which is a near-Earth object detection program operated by the University of Arizona’s Steward Observatory which uses a 1.5-meter (60-inch) Cassegrain reflector telescope at Mount Lemmon Observatory in Arizona to take repeated images of the sky. On January 3, 2025 the survey recorded a magnitude 21.5 dot of light, and follow-up observations quickly revealed it was displaying cometary activity. This led to its official designation as a comet – Comet C/2025 A6 (Lemmon).
More observations of the comet allowed astronomers to calculate its orbit, and they found that it had last visited the inner Solar System over a millennium ago. That was interesting, but the big question – as always with a newly-discovered comet – was “How bright is it going to get?” More calculations suggested that it would only reach around magnitude 10 when it was at its closest to the Sun in early November, meaning it would be an easy target for experienced amateur observers, but nothing for anyone else to get too excited about, and as the comet was temporarily lost from view in the Sun’s glare, as it passed through solar conjunction on July 2, no-one really expected very much from it when it reappeared.
However, comets love defying the expectations of those who observe and study them – and write about them – and they love proving them wrong even more. So when A6 re-emerged into the morning sky in mid-August 2025, and was far brighter than expected, possibly due to an outburst of activity on its nucleus, usually-pessimistic comet observers began to look at it with more interest. No-one was predicting it would be another Hale-Bopp, or even as good as Comet A3 which was such a lovely sight a year ago, but its appearance and behaviour prompted guarded speculation that it might be a very pleasing sight in binoculars at the end of October, when it would be best placed for observation from Earth.
Now, as October gets into its stride, many observers are becoming quite optimistic about A6’s prospects.
It is currently circumpolar as seen from mid-UK latitudes – meaning it is close enough to the Pole Star that it never sets – and although it is visible low in North West after sunset, it is best seen in the morning sky, when it reaches a decent elevation several hours before sunrise. It can be found on the border between Ursa Major and Leo Minor, and is reportedly shining at around 7th magnitude ( I say “reportedly” because the weather where I live here in Cumbria has been so rotten for the past week that I haven’t seen it myself in that time, so I can’t confirm its brightness personally), though some observers blessed with very clear, very dark skies place it as high as 6th magnitude. It is clearly visible in binoculars and small telescopes, but hasn’t reached naked eye visibility yet. Will it? Well, if it keeps brightening as it has been doing it is on track to reach 3rd magnitude at the end of October, maybe even 2.5. That would make it visible to the naked eye for those blessed with good eyesight and dark, light pollution-free skies, and easily visible through binoculars and telescopes for others not quite so lucky.
(Above: Comet A6 Lemmon imaged from Kendal, Cumbria in the early hours of September 24th using a Seestar S50)
The comet has now developed a quite lovely gas tail, with several distinct braids and streamers within it. It can already be measured out to a length of an impressive 12 degrees on long exposure photographs, which is hopefully a good sign for the future. In fact, some computer simulations suggest A6 might grow a dust tail several degrees long and, at its best, a gas tail many degrees long, although such a tail would probably only show up clearly on long exposure photographs and not be visible to the naked eye.
Over the next couple of weeks the comet will drift beneath the stars of the Big Dipper/The Plough, that famous asterism within Ursa Major, gradually getting brighter and growing a longer tail. It will be best seen in the evening sky from mid-October, when it will be visible quite low in the North West as the sky darkens after sunset. It will then be moving beneath the curved handle of the Big Dipper/The Plough, heading eastwards towards the bright star Arcturus, which it will pass above on October 22nd/23rd. After that it will continue eastwards, dipping down beneath Corona Borealis. By the time it reaches perihelion – its closest point to the Sun – on November 8th it will be in southern Ophiuchus, already low in the South West at sunset and setting only a couple of hours later.
What will it look like then? How bright will it be? How long will its tail be? We don’t know, and no-one with any sense is trying to predict that yet. We’ll just have to wait and see.
But it’s very important to not get carried away. We are still very much at the “might”, “could be” and “possibly” stage with this comet, so predicting its future brightness and appearance is not wise, However, we do know, for a fact, that it is not going to “streak across the heavens!” or “light up the sky!” like the coverage on social media is saying. If you read something like that about its future, ignore it. The future will take care of itself.
For now, Comet A6 Lemmon is visible in the morning sky for northern observers, is already bright enough to be seen as a small, fuzzy, greenish star through binoculars and small telescopes, and can be photographed using very basic equipment. I imaged it on several clear mornings before the bad weather set in, and managed to get pictures with just my Canon DSLR on a very basic motorised tracking mount. I also managed to image it with my Seestar S50 Smart telescope, which picked up its then still faint, short tail (see above) so I’m looking forward to getting more up to date images of its now much longer tail once… if… the Cumbrian clouds part; going by the image taken of it by my friend Monika Landy-Gyebnar from Hungary a couple of days ago (see below) it’s now quite a sight…
So, during the month ahead, try to get out and see this comet. If it becomes visible to the naked eye we might be in for a treat, but even if it doesn’t get that bright it should still be a lovely sight in binoculars.
Good luck, comet-hunters, wherever you are!
Stuart Atkinson
(Below: Image credit Monika Landy-Gyebnar)
