Have you heard about Comet C/2023 A3 (Tsuchinshan-ATLAS) yet?
Comet observers are all hoping for big things from comet C/2023 A3 (Tsuchinshan–ATLAS) in autumn 2024.
When it was discovered, it was hailed as a potential ‘comet of the century’ and calculations suggested it might become as bright as mag. -4!
It’s now thought that at best A3 will reach mag. +0.4, a lot fainter but still much brighter than the last really bright comet, C/2020 F3 (NEOWISE), which delighted sky-watchers in summer 2020.
Perhaps you were excited by observations of Comet 12P/Pons-Brooks, but that comet is now only visible from the Southern Hemisphere.
Well, no promises, but towards the end of 2024 we might have a comet in the sky as bright as E3 was, or brighter.
If the most optimistic predictions are to believed it might even be the best comet for a long time. There are even whispers of it being a Great Comet!
But calm down. It’s far too soon to be making predictions like that.
You might have noticed that after the initial supernova burst of hype about how it could become the 'comet of the Century' and all the wild predictions of how it was destined to 'blaze in our night sky brighter than the Moon', things have gone rather quiet around Comet C/2023 A3 (Tsuchinshan-ATLAS).
Comet C/2023 A3 (Tsuchinshan-ATLAS) quick facts
To recap, 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.
Unfortunately, as is the case so often with astronomy stories these days some in the media added two and two and got 100, and 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 very clear from the start that a celestial spectacle was absolutely 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 who actually knew what they were talking about.
And that’s what’s been happening quietly over the past few months.
Is the comet fizzling out?
As Comet A3 has drifted slowly and silently through the constellation of Virgo, heading for neighbouring Leo, comet watchers and photographers around the world have been keeping a close eye on it, patiently checking its progress and development.
And what have they found?
Well, although Comet A3 is now bright enough to be seen easily through small telescopes, and can be imaged using just a DSLR fitted with a long lens, tracking the sky on a motorised mount, the predicted brightening of this icy visitor appears to have stalled; it seems to have been shining – if that’s the right word – at around 10th magnitude for a couple of months now.
Now before any “I KNEW IT! It’s Comet ISON all over again!” wailing or gnashing of teeth begins, this doesn’t necessarily mean the comet is going to fizzle out and leave us all feeling disappointed and cheated.
Comets are very unpredictable creatures at the best of times, and they like to worry us.
Many comet experts are putting A3’s reluctance to brighten down to the angle at which we’re seeing the comet, or other factors.
Doom and gloom reports of Comet A3’s passing have been greatly exaggerated.
But having said that, it would be wrong to not acknowledge that some comet watchers are becoming a little… concerned about Comet A3’s prospects.
It’s possible that it just isn’t as physically active a comet as it needs to be to become bright to the naked eye later this year, or that it was having an outburst of activity when it was discovered, which skewed predictions.
We don’t know. We can’t know, not yet, not when it is still so far away, still almost a quarter of the way between Mars and Jupiter.
But we do know that it’s far too early to write it off yet!
Observing Comet C/2023 A3 (Tsuchinshan-ATLAS) over the coming months
So what do we do? We’ll just have to wait and see what happens, and keep a close eye on it.
That’s all we can do. Images of the comet taken recently show it has a small, curved tail that is well worth looking for if you’re blessed with a clear sky.
Having said that, keeping a close eye on Comet A3 is becoming more and more difficult.
It is still in Virgo, but only just, and as I write this it is just a couple of days away from crossing the border into neighbouring Leo.
This makes it an evening object for northern observers, but it is already quite low in the south west as the Sun sets.
By the time the sky gets bright enough to make looking for it worthwhile it is VERY low in the sky and very challenging – but not impossible! – to track down before it sets in the early hours of the morning.
If you want to see A3 you’ll have to get a move on; the comet’s visibility will worsen steadily now as the days and weeks pass.
By the start of July it will be setting just two hours after the Sun, and very hard to see.
By mid-July it will be setting barely an hour after the Sun, and soon after that it will be lost in the Sun’s glare altogether.
And then? And then we cross our fingers and wait until it reappears in the pre-dawn sky at the end of September.
How it looks then will give is a much clearer idea of what it will look like at its best.
Hopefully the early predictions that it will be easily visible to the naked eye will prove to have been accurate, and then we can quietly begin to look forward to seeing something lovely in the night sky after sunset during mid-October.
But be aware that there’s always a chance that after rounding the Sun A3 will be too faint to see without binoculars or a telescope.
So, although you might not be hearing much about it right now, Comet A3 is still there, and although its reluctance to brighten is causing concern in some quarters, it’s far too early to write it off.
But crossing your fingers won’t hurt..!
If you'd like to observe it yourself, read Pete Lawrence's fantastic guide on how to locate Comet C/2023 A3.
The story so far
The ball of ice and dust that has eyebrows raising and hopes rising is called C/2023 A3 (Tsuchinshan-ATLAS).
It 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 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.
Following the long-established naming convention it was given a name honouring both its discoverers: C/2023 A3 (Tsuchinshan–ATLAS).
Why everyone's talking about C/2023 A3 (Tsuchinshan-ATLAS)
Comet A3’s orbit will bring it close enough to both the Sun and the Earth in September/October 2024.
There is good chance it will be visible to the naked eye, and has the potential to be a bright naked-eye comet.
It’s easy to get carried away by this, but perhaps understandable. It’s far too long since we had a really bright comet in the sky.
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 will be 'another Hale-Bopp' is being very unwise. It’s still far too early to know what it will do, and how bright it will be.
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 it will be a morning object, perhaps shining as brightly as mag. +0.6, but rising just before the Sun.
Our best views of A3 will come when it moves up into the evening sky around 10 October.
By then it will have faded slightly, but is predicted to still be as bright as mag. +0.8, low in the west after sunset.
Hopefully by then it will have grown a tail, but we can’t count on that.
By mid-October the comet will still be a first-magnitude object, setting almost three hours after the Sun.
It should be a lovely sight to the naked eye and in binoculars and telescopes too.
Perihelion
Comet C/2023 A3 will reach perihelion - the closest point to the Sun in its orbit - on 28 September 2024.
If it behaves itself, early summer 2024 it should start to become visible in the evening sky through small telescopes.
It might be bright enough to be visible through binoculars or even to the naked eye in late September 2024, when it will be a pre-dawn object, very low in the east before sunrise.
Will it have a tail by then? We don’t know. It all depends on how old and how active the comet is, and experts are still figuring all that out.
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.
How bright will C/2023 A3 get?
How bright will the comet be during mid-October 2024?
Some experts are suggesting it might reach first or even zero magnitude, making it obvious to the naked eye (for info on what this means, read our guide to stellar magnitude)
Others are saying we'll be lucky if it's even third, which would make it 'another E3' not 'another Hale-Bopp', only visible to most people through binoculars. We just don’t know.
If this all sounds very vague, that’s just the way it is. Comets are hard to predict, and have a habit of not living up to expectations.
The comet is a long, long way away, and not doing much yet.
But as it gets closer, and more and more people see and photograph it, we’ll have a better idea of what it will do when it approaches and then passes us late in 2024.
Keep checking back on this page. We’ll keep you updated!
Find out more about the comet via the International Astronomical Union's Minor Planet Center or at astro.vanbuitenen.nl/comet/2023A3.
