Comet C/2023 A3 (Tsuchinshan–ATLAS) is set to take centre stage in October 2024.
A much-anticipated object, C/2023 A3 is predicted to be above naked-eye brightness during October.
After swinging rapidly through its closest approach to the Sun (perihelion) in late September, in October we'll get to see the aftermath of its solar encounter.
Find out more in our guide to comets and asteroids visible tonight
Perihelion occurs on 27 September, when C/2023 A3 passes 58.6 million kilometres from the Sun, a similar distance as Mercury’s orbit.
This is the comet’s first close encounter with our star, having travelled to the inner Solar System from the Oort cloud, a theorised outer region 2,000–200,000 AU (0.03–3.2 lightyears) from the Sun.
It’s thought the Oort cloud contains trillions of potential comets.
Observing Comet C/2023 A3 in October
After C/2023 A3’s long journey sunward, what happens around perihelion is still unknown.
In the early part of 2024, the comet showed a lot of dust activity which, if it continues, may give it an impressive tail.
Comet C/2023 A3 (Tsuchinshan–ATLAS) appears just 3° north of the Sun on 9–10 October, far too close to observe.
However, its apparent separation from the Sun then increases rapidly.
Clear skies and a flat western horizon will be key from mid-October.
Those that are lucky enough to have that may pick the comet up on 11 October, but it will be extremely low as darkness falls and difficult to see.
The comet’s closest approach to Earth, at 43.9 million kilometres, occurs on 12 October.
On 13 October at 20:00 BST (19:00 UT), the comet will be 4° above the western horizon under deep twilight as seen from the centre of the UK.
This increases to 6° at the same time on 14 October and 9° up on 15 October, again at 20:00 BST (19:00 UT).
Meetings with other celestial objects
There’s a photo opportunity on 15 October, when Comet C/2023 A3 (Tsuchinshan–ATLAS) will be 1.4° from the globular cluster M5.
If you want to capture it, read our guides on how to photograph Comet C/2023 A3 and how to photograph a comet.
When it’s close to the Sun in the sky, ‘forward scattering’ may further increase the comet’s apparent brightness: basically the comet’s dust particles redirecting sunlight into your line of sight.
One caveat for the mid-month period will be the presence of a bright Moon further to the east, reaching its full phase on 17 October.
C/2023 A3’s altitude improves throughout the rest of October, its brightness dropping from a predicted second magnitude on 11 October to third magnitude on 15 October and sixth magnitude by the end of the month.
Ultimately, we’ll have to wait and see what happens, but one thing is for sure: there’s going to be lots of attention on this particular object
Let’s keep our fingers crossed for clear skies.
If you're following Comet C/2023 A3 (Tsuchinshan–ATLAS) in October 2024, share your observations and images with us by emailing contactus@skyatnightmagazine.com
