Could Comet A3 become another Great Comet, or even simply reach naked-eye brightness? We’ll find out soon…
Comet observers are all hoping for big things from comet C/2023 A3 (Tsuchinshan–ATLAS) over the coming days.
You might have noticed that there have been a flurry of observations and images of Comet C/2023 A3 (Tsuchinshan-ATLAS) posted online recently, and wondering what all the fuss is about.
In this guide we’ll reveal what’s going on, where the comet is and what we can expect.
For more info, read our beginner’s guide to Comet C/2023 A3, discover the 10 greatest comets of recent times and find out what comets and asteroids are in the sky tonight
Comet C/2023 A3 (Tsuchinshan-ATLAS) quick facts
Long period comet C/2023 A3 (Tsuchinshan-ATLAS) was spotted in February 2023, during a sky survey performed by ATLAS – the Asteroid Terrestrial-impact Last Alert System – using the 0.5-m f/2 Schmidt reflector telescope operated at the Sutherland Observatory in South Africa.
Back then it was an uninspiring 18th magnitude spot on a photo and was given the equally uninspiring name ‘A10SVYR’.
When its orbit was calculated, it was noticed that it had already been spotted by the Purple Mountain Observatory in China on 9 January 2023, when it was magnitude 18.7.
Follow-up observations revealed A10SVYR had a short tail, so it was designated a comet, and following the long-established naming convention it was given a name honouring both its discoverers: C/2023 A3 (Tsuchinshan–ATLAS).
Why did it cause so much excitement, when comets are now discovered daily?
Because crunching the numbers showed that Comet A3’s orbit would bring it close enough to both the Sun and the Earth in September/October 2024.
There was a good chance it would be visible to the naked eye, and had the potential – if everything turned out right – to be a bright naked-eye comet.
See the best images of comet C/2023 A3 Tsuchinshan-ATLAS
Unfortunately, as is the case so often with astronomy stories, some in the media added two and two and got 100.
Soon social media was groaning under the weight of posts and stories looking forward to the arrival of the most spectacular comet since Hale-Bopp graced our skies all those years ago.
Of course, we were very careful to not buy into this silliness.
We made it clear from the start that a celestial spectacle was not guaranteed, and we wouldn’t be able to predict the comet’s visual appearance in 2024’s autumn sky until more detailed and accurate observations had been made by experienced astronomers.
And that’s what’s been happening over the past year.
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As October began, it was hard to believe that the tiny, out-of-focus star we were all looking at on grainy, tracked and stacked images a few months ago had grown into a quite stunningly beautiful comet, with a fifteen-degree long tail shooting up from the horizon like a search beam…
Although that glorious view of Comet C/2023 A3 was only available from the southern hemisphere, where the comet is a second magnitude, whip-tailed star shining in the twilight sky before sunrise and clearly visible to the naked eye, observers positioned in countries as far north as Spain, Italy and even France have been able to see the comet too.
In the past week or so many of them have glimpsed the comet as a fuzzy star shining low in the marmalade orange pre-dawn sky.
Find out more with our guide to observing Comet C/2023 A3 in October.
Unfortunately the comet was so low in the sky before sunrise from latitudes further north that only a handful of dedicated – and lucky! – imagers were able to capture it on camera from the UK and US states north of Florida.
The images taken of the comet over the past two weeks have been quite beautiful.
Wide-angle views have shown it as a thin, slightly curved vapour trail to the right of the Moon, looking very much like one of those classic comets from years gone by.
After processing, zoomed-in images taken through longer lenses and telescopes have shown fascinating and intriguing detail within the comet’s long dust tail.
They’ve also shown a delicate, powdery blue gas or ion tail spiralling away from the head, too faint to see with the naked eye – yet.
And the very latest images show yet more dusty material fanning away from the other side of the tail.
We’ve even seen an image of Comet A3 captured by NASA’s SOHO telescope.
Now Comet A3 is moving up into the northern hemisphere’s evening sky.
All those northern observers who have been desperate to see Comet C/2023 A3 will have their chance to gaze at it through their binoculars and telescopes, and turn their cameras towards it too – weather permitting, of course.
What can we expect from Comet A3?
Comet C/2023 A3 shows no signs of falling apart, or fading, or springing any other nasty surprises on us before it claws its way out of the sunset glow.
So it looks like northern observers are in for a treat from around 12 October 2024: a naked-eye comet, with a tail long and bright enough to be visible to the naked eye, shining in the west as twilight deepens.
Just how bright it will be we can’t know in advance, though some have predicted the comet will reach first magnitude thanks to the phenomenon known as ‘forward scattering’.
As for the length of its tail, we can’t know that in advance either, but all the signs are that it will be long enough to pick up easily with the naked eye, and fascinating through binoculars and telescopes.
I’ve even seen one prediction of a tail 30 degrees long!
And if the computer models are correct, Comet C/2023 A3 could grow a spike-like ‘anti-tail’ from the front of its coma, too.
There was a lot of hype about Comet C/2023 A3 when it was discovered in 2023.
Within days the internet was awash with predictions that the “comet of the century” was on its way, and that in October 2024 skywatchers and stargazers would be “dazzled” by it.
A3 is not the Comet of the Century, and no-one is so dazzled by it that they have to wear sunglasses.
But it is already a truly beautiful comet, as we can see from the amazing images being captured of it.
See? Not all comets are destined to disappoint us!
Comet C/2023 A3 – the story so far
When we reported on the comet back in early September 2024, we were pleased to be able to write that Comet C/2023 A3 (Tsuchinshan-ATLAS) hadn’t actually vanished, and contrary to recent reports suggesting Comet C/2023 A3 is doomed, it hadn’t shown any signs of falling apart.
Comet C/2023 A3 (Tsuchinshan-ATLAS) was lost to visual observers over the summer of 2024, when it became too close to the Sun to be seen from either the northern or southern hemisphere.
That left comet watchers to cross their fingers that it was continuing to increase in brightness.
It was visible to several of the satellites that monitor activity on and around the Sun, but not in any detail, just a few trailed pixels really.
So comet observers around the world were waiting anxiously for it to reappear in the sky in September.
We knew from calculating the comet’s orbit and track across the sky that observers in the southern hemisphere would be the first to be able to see the comet again, around mid-September.
Southern comet observers were scanning and sweeping the morning sky before sunrise, hoping to recover it, and crossing their fingers it would still be in good shape and on track to be visible to the naked eye in October 2024.
If it was fainter than predicted that could have been bad news…
On the morning of 11 September 2024, veteran comet observer Terry Lovejoy photographed the comet in the morning sky from Wellington Point in Australia.
On his stack of 30x 1.3 second exposures taken with a 135mm lens the comet can be seen clearly, even though it was just 14 degrees from the Sun. He estimated the comet’s magnitude to be around +5.5.
A day later another veteran comet observer and photographer, Michael Mattiazzo, imaged the comet, also in the Australian morning sky, and put its magnitude a little brighter, perhaps 5.2.
As we had hoped, during its absence from our skies Comet A3 continued to develop as predicted.
In the worst case scenario, Comet A3 could “do an ISON” and fall apart as it rounds the Sun, leaving only a cloud of dust behind and cheating us of the sight of a very attractive comet in our sky.
Or, Comet C/2023 A3 may do nothing special or unexpected.
It could survive its passage around the Sun intact, but then, instead of unfurling a long tail behind it and brightening to first magnitude, just grow a short tail and only reaches 3rd or even 4th magnitude.
Comet A3 would still be bright enough to be visible to the naked eye, and would definitely be enjoyed by amateur astronomers using binoculars, telescopes and cameras, but, like most comets, it wouldn’t be obvious to non-astronomers.
Whatever happens, one thing is for sure – Comet A3 is very unlikely to become the ‘Comet of The Century’ many reports on social media are predicting.
Why everyone’s talking about C/2023 A3 (Tsuchinshan-ATLAS)
You might remember how beautiful Comet Hale-Bopp was back in 1997.
Even if you didn’t see it yourself, if you speak its name at an astronomy society meeting you’ll see many people smile, as fond memories of seeing its twin tails painted on the spring sky come flooding back.
But anyone predicting A3 would be ‘another Hale-Bopp’ was unwise.
What we know about C/2023 A3 (Tsuchinshan-ATLAS)
Initial data seems to suggest that Comet C/2023 A3 completes an orbit every 80,000 years.
By the end of September 2024 it became a morning object and reached perihelion – the closest point to the Sun in its orbit – on 28 September 2024.
Our best views of A3 will come when it moves up into the evening sky around 10 October.
We’ll lose sight of the comet early October 2024, when it passes close to the Sun as seen from Earth.
Some are wondering if A3 will be visible in the daytime, by blocking the Sun.
But they wondered the same thing about Comet ISON a few years ago and that never happened!
So let’s not even go there now.
If the comet survives its passage around the Sun, the main northern observing period will begin after 11 or 12 October 2024.
Then the comet moves up into the evening sky, visible after sunrise, a little higher and easier to see each evening.
Keep checking back on this page. We’ll keep you updated!
If you observe or photograph Comet C/2023 A3 Tsuchinshan-ATLAS, share your observations and images with us by emailing contactus@skyatnightmagazine.com
Find out more about the comet via the International Astronomical Union’s Minor Planet Center or at astro.vanbuitenen.nl/comet/2023A3.