Could Comet A3 become another Great Comet, or even simply reach naked-eye brightness? We’ll find out in autumn 2024…
Comet observers are all hoping for big things from comet C/2023 A3 (Tsuchinshan–ATLAS) in autumn 2024.
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
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.
Latest news
Comet C/2023 A3 (Tsuchinshan-ATLAS)hasn’t actually vanished, and contrary to recent reports suggesting Comet C/2023 A3 is doomed, it hasn’t shown any signs of falling apart, but it is as of early September 2024 now so close to the Sun in the sky that it’s extremely hard to see.
Comet-watchers won’t get a good look at it again now until mid to late September, when it will be visible from the southern hemisphere, unless it does suffer some kind of break-up between now and then, but that’s looking increasingly unlikely.
Encouragingly, recent reports suggested A3’s brightness, which had stalled worryingly for a while, had reached a very healthy magnitude 7, and images taken under dark African skies at the start of the month showed it sporting both a long, narrow, blue gas and a broader, more yellow-hued dust tail.
But now all we can do is wait and see what happens. Looking into the cosmic crystal ball there are basically three future scenarios.
The best case scenario is that Comet C/2023 A3 behaves itself and continues to brighten and develop as it nears the Sun.
If it does this, it might grow a decent tail, long enough to poke up above the eastern horizon before sunrise in late September.
Then, if it survives its screeching handbrake-turn around our star it could become a bright, naked eye comet in the evening sky from early October, sporting a 20-degree-long tail and perhaps an Arend-Roland like spiky anti-tail too.
The phenomenon known as ‘forward scattering’ could enhance its brightness to the point where, at its best, it shines at first magnitude, making it obvious and easy to find in the sky even for non-astronomers.
We’d all take that I’m sure!
However, 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.
This is looking much less likely now, but it would be unwise to discount the possibility altogether.
In the middle of those two scenarios, Comet A3 doesn’t do anything special or unexpected.
It survives its passage around the Sun intact, but then, instead of unfurling a long tail behind it and brightening to first magnitude, it just grows a short tail and only reaches 3rd or even 4th magnitude.
This is what many comet experts and veteran observers are predicting and have done from the start.
In that scenario, 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.
With more than a month to go until the comet is at its best – whatever its best turns out to be – there are already a ridiculous number of posts on the major platforms declaring how it will “light up the sky!” and “dazzle stargazers!”, and more appear every day.
The best thing to do is ignore those and forget about the comet for a while, because we simply don’t know for sure what it’s going to do.
If it becomes bright enough to be seen easily with the naked eye in October that will be brilliant!
But even if it is too faint to see well without binoculars it will still be a welcome and fascinating visitor to our night sky.
So now we wait. There’s nothing we can do. Like all comets, A3 will do what it does. But crossing your fingers can’t hurt…
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 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 2024 it will be a morning object, perhaps shining as brightly as mag. +0.6, but rising just before the Sun.
Comet C/2023 A3 will reach 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.
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 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.