Comet C/2025 A6 Lemmon has been delighting northern hemisphere skywatchers for over a month, but now it is moving into the southern sky and inevitably comet-watchers are feeling a bit, well, lost.
What are they supposed to look at now? Thankfully, another comet is visible in the northern sky, and although it’s very faint – much fainter than the just-departed Comet Lemmon – it’s very special indeed.
An extrasolar visitor
Unless you’ve been living under a rock on Mars for the past five months, you’ll know that a comet called Comet 3I/ATLAS has been all over the headlines.
Why? Because unlike Lemmon, Hale-Bopp, Halley, and every other comet you’ve ever heard of, it’s not a member of our Solar System.
3I/ATLAS is an extrasolar comet. It was formed around a star in another system beyond our own, so long ago and so far away that it's taken millions, perhaps billions of years to reach us.
But now that it has reached our neck of the celestial woods, it’s not staying long.
After screeching into our Solar System, it's going to head off into deep space again, leaving our Solar System behind, continuing its epic, lonely journey through the Milky Way.
This is understandably very exciting for astronomers.
The comets belonging to our own Solar System are fascinating objects, and studying them tells us a lot about the history and evolution of the Sun and the planets which orbit it.
Indeed, the opportunity to study a comet from another star entirely – a comet perhaps twice as old as our own Solar System (some estimates suggest 3I/ATLAS is seven billion years old) has got them quite giddy with anticipation.
But unfortunately, they’re not the only ones feeling giddy...
In this blog, we'll update you on the progress and visibility of Comet 3I/ATLAS before it disappears from view at the end of 2025.
But before we get started, we need to address the comet-sized elephant in the room.
It's never aliens
At the end of the film The Martian, modern-day Robinson Crusoe astronaut Mark Watney stands before his first ever class of trainee astronauts and tells them that yes, he did survive alone on Mars by eating potatoes grown in his own… faeces… and yes, it was as disgusting as it sounds, and he’s never going to talk about it again.
So, let’s get the 3I/ATLAS nonsense out of the way, and never speak about it again.
Despite what conspiracy theorists are saying on social media and on TV, and despite what certain alien-obsessed 'scientists' are saying, 3I is not an alien spacecraft.
It has not 'baffled NASA' by changing direction; it is not made of metal; it is not flashing, or changing colour, or beaming signals to Earth; it is not a probe sent by an alien species to study Earth; NASA is not hiding images taken of the comet from Mars or by telescopes orbiting the Earth.
Okay, that’s out of the way. Like Mark Watney’s botanical triumphs, we won’t speak about that again.
If you want more on this, though, read astronomer Mark Norris's thorough explanation on why Comet 3I/ATLAS isn't aliens.
What we do know about 3I/ATLAS
The truth is, Comet 3I/ATLAS is just that: a comet.
3I/ATLAS was discovered on 1 July 2025 by the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope in Río Hurtado, Chile.
Follow-up observations from other observatories revealed it's the third confirmed interstellar object to visit our Solar System, after the famous 1I 'Oumuamua in 2017 and comet 2I Borisov in 2019.
After months of study, we now believe that 3I’s nucleus is around 5.6km (3.5 miles) across, but could possibly be as small as only 1.1km (0.7 miles).
Measurements of the comet’s composition show unusually large amounts of carbon dioxide and unusually high nickel levels.
But in general, it really is a typical comet, with typical cometary volatiles like water, dust and carbon monoxide. Nothing too exciting there, to be honest (at least, for the general public, anyway).
The real excitement comes from studies of its trajectory. That suggests it was born in – and then ejected from – a star system far away in the Milky Way.
And it could be over 7 billion years old, predating the birth of our own Solar System by billions of years.
It's not just a cosmic fossil, it’s a fossil of a fossil.
A general word on observing 3I/ATLAS
Until the weekend of 8/9 November, even the very best images we had of 3I/ATLAS showed it as little more than a tiny smudge, with perhaps a hint of a wisp of a tail.
That's hardly surprising, seeing as it was so small, so dark, so far away and travelling so fast as it whooshed towards and then behind the Sun.
While it was behind the Sun, spacecraft on Mars managed to catch a glimpse of 3I/ATLAS, keeping an eye on things while it vanished from view on Earth.
But as of mid-November, the comet has emerged from behind the Sun, and the same experienced and skilled astrophotographers who took such wonderful images of Comet Lemmon before are now turning their attention and cameras towards 3I.
The images they're taking are fascinating. They show several distinct tails or plumes coming off its nucleus. Another, spike-like 'anti-tail' is also visible in the images.
These images show the nucleus of 3I is very active, and in the days and weeks ahead, as the comet gets closer to Earth, we’ll see better and better images with more detail.
The comet will be observed by an increasing number of telescopes too. A very exciting prospect indeed.
That’s all enthralling, but will backyard amateur skywatchers and comet chasers be able to see this rare visitor themselves?
While Comet 3I is never going to become bright enough to be visible to the naked eye – not even from the darkest skies on Earth – it should grow bright enough to be seen through amateur telescopes and imaged using cameras.
It should also be visible through the new generation of smart telescopes, like Seestars and Dwarfs, etc.
In fact, if you are a northern hemisphere observer with a medium to large aperture telescope, or a good astrophotography rig, Comet 3I/ATLAS is there waiting for you now.
In our regularly-updated blog, we'll reveal how to see it. Scroll down further for past entries.
16 November
I finally managed to capture an image of comet 3I/ATLAS, the third confirmed interstellar visitor to our Solar System, which had long been reserved for only the largest, most sophisticated astronomical gear.
Excitingly, this is now changing, as I managed to image it on the morning of 16 November 2025 from the centre of light-polluted Kendal, Cumbria, UK, using my Seestar S50 smart telescope.
I woke up at 4.30am to a freezing, frosty sky and headed down to the river, despite knowing the odds were stacked against me, given the comet was low in the sky, scraping the treetops, close to the bright Moon and various streetlights.
Since the comet wasn't yet in my Seestar's database, I manually star-hopped to the area of Virgo, but my first images were, frankly, awful, covered in streaks of glare.
Yet there it was: a tiny, fuzzy smudge down in the corner, confirmed to be the magnitude 10 comet.
I spent the next hour dodging streetlights to take more exposures until dawn finally washed it from view.
My resulting pictures may only be a smudge, but they represent a 'snatched portrait' of a billions-of-years-old interstellar wanderer, taken with a relatively humble telescope
Read the full story in my article on how I finally managed to photograph comet 3I/ATLAS.
11 November
As we approach mid-November 2025, Comet 3I/ATLAS can be found drifting slowly through the zodiacal constellation of Virgo.
At this time of the year, Virgo is an early morning constellation, rising in the east before sunrise, so if you want to see Comet 3I/ATLAS you’ll either have to stay up very late or get up very early.
It is very small visually – little more than an out-of-focus star – and is shining, if that’s the right word, at around magnitude +12.
In the weeks ahead, 3I will gradually climb higher into the morning sky, moving out of Virgo and up into neighbouring Leo.
When it is at its closest to us, on 19 December 2025, 3I will be rising around 23:00 and located not far from Regulus, the brightest star in Leo. That should make it relatively easy to find and photograph.
How bright will it be then? Well, we can’t know that.
It will still be over 270 million km away – twice as far away as Mars is when it’s at opposition – so it won’t be visible without a telescope, and you’ll need to take long exposure images to photograph it.
By Christmas 2025, Earth will be in 3I’s rear-view mirror as the comet heads back off into space, leaving us behind.
In the centuries and millennia to come, it will probably pass through other systems and swoop around other stars: stars so far away that our own Sun will be just a speck of light in the night skies of the worlds of any beings out there to witness its brief visit.
But that’s for the future. As of mid-November, if you want to see 3I/ATLAS, you need to be looking to the east before sunrise, where the constellation of Virgo is rising.
There, if you have the right equipment, you’ll find a tiny smudge of light that is one of the rarest, most fascinating things ever seen in Earth’s sky.
Not an alien spacecraft, but very definitely a visitor from not just the depths of space, but the depths of time, too.
We’ll keep you informed of the comet’s position, appearance, and activity via this blog, so keep checking back regularly.
If you manage to see or photograph 3I/ATLAS, get in touch by emailing contactus@skyatnightmagazine.com
