Where to look for comet C/2023 A3

Robin Scagell Top stories

Comet 2023 A3 Tsuchinshan-ATLAS is becoming visible in the evening sky in the UK during October 2024. Following its closest approach to the Sun on 27 September the comet will fade as it climbs into the evening sky but should be visible with binoculars or photography if you know where to look. But where exactly should you look?

Although the comet is closest to Earth on 12 October, it will remain visible throughout October and may even be better visible after its closest approach as it will then appear in darker skies. To start with it will only be visible shortly after sunset, but after about 14 October it will be visible for more than an hour, although still low down, so you’ll need a good horizon to the south-west to be able to see it. Here’s a map of its positions during October 2024.

Positions of Comet C/2023 A3 during October 2024, as seen from central UK. The comet positions are shown for 00.00h on each date, so in the evening the comet will be closer to the next day’s position. The horizon and position of Venus are shown for 12 October at the start of nautical twilight, at 18:50 BST. Map based on SkyMap.

What to look for

Bear in mind that the comet will appear as a stationary fuzzy object, and that any tail might not be easily visible by eye. If you see something that you think is a comet, moving quickly through the sky, it’s most likely to be an aircraft with a condensation trail. Although the comet is moving quickly through space, it is at least 70 million km away even at its closest, so the movement is only visible from night to night.

Although the comet is predicted to be about as bright as Arcturus on 12 October, this figure is for its total brightness and its appearance with the naked eye when low in the twilight sky will be very much fainter as its light is spread over a much larger area. A lot also depends on the clarity of the atmosphere at the time – the typical milky UK sky doesn’t help. Later in October when the comet is higher up and in a darker sky its predicted total brightness will be around magnitude three, which is about as bright as the faintest star in the Plough.

Some phone sky apps will show the comet and will help you to find it, as long as their direction sensors are accurate. You might be able to see Venus, which is very bright but low down, which will help you find the right part of the sky, and also Arcturus, which is one of the brightest stars in the sky. Binoculars will help, and in many cases a photo on your phone will show the object better than the naked eye.

Also take into account that objects in this part of the sky are setting, so don’t leave it too late to start looking. Don’t try looking when the Sun is in the sky, as viewing the Sun directly can risk eye damage.

During the second half of October as the comet appears in a darker sky you can look somewhat later in the evening, still using Arcturus as your guide.

Photographing the comet

Good quality phone cameras may show the comet better than you can see with the naked eye. A conventional camera used with an exposure time of a few seconds may also reveal the comet as well as a significant tail. For the best results you’ll need a telephoto lens setting, ideally with the camera tracking the comet on a suitable tracking mount aligned on the north celestial pole, or using a modern smart telescope that automatically aligns itself on the sky before taking time exposures.

Comet Gallery 12 October

Kevin Quinn of Piddletrenthide, Dorset, at 19:28 using a Google Pixel 7a.
Jim Smith, from Hergest Ridge, Shropshire, using a Nikon D500 with 155 mm lens at f/8, 0.8 sec at ISO 800, 19:23 BST.
From the grounds of Guildford Cathedral, Surrey, by Andrew Whiter. Canon EOS R, 300 mm f/5.6 lens, ½-sec at ISO 1600, 19:27 BST.
John Axtell’s image at 8:01 BST. Canon 550D, 2 sec exposure with 250 mm f/6.3 lens at ISO 1600. Along the River Wey between Pyrford and Ripley, Surrey.
Graham Cluer took this photo from Kenley, Surrey, at 19:31. Canon EOS R6m2, 400 mm f/8 lens, 1.3 sec at ISO 12,800.
A gap in the clouds in St Albans allowed this shot by Martin Lewis with a Canon 500D with zoom lens set to 250mm, f5.6. 5 sec at ISO 100

17 October

Over Robin Scagell’s observatory near High Wycombe at 19:36 BST, taken with Sony A7S, 28 mm f/2 lens, 2 sec at ISO 1000. Full Moon. The comet was not visible with the naked eye but could be spotted with 10 x 30 binoculars.
Closeup at 19:17 BST with FMA 180 f/4.5 lens and ZWO ASI294 astro-camera. 30 sec driven exposure. An ‘antitail’ is visible, apparently in front of the comet’s head. This is a perpective effect as a result of Earth passing through the plane of the comet’s tail, which spreads out in a fan behind it rather than being a narrow stream of material. Robin Scagell
John Fletcher of Gloucester reports ‘nice naked eye comet seen from my home near the end of twilight, despite bright full moonlight and light pollution. A tail of several degrees in length seen easily in binoculars.’ 19:10. Taken with Canon R5, 85 mm prime lens. ISO1000, 1 second exposure, f/2.

19 October

Closeup of the head of the comet, cropped from image made with Askar 180 mm f/4.5 lens and ZWO ASI294 astro-camera from near High Wycombe, Bucks. Robin Scagell.

22 October

Yuti Chernajovsky of Whitstable, Kent, took this 8-second exposure using a Nikon 850D with a 40 mm f/4 lens at ISO 1250. The star to the right of the comet’s head, 45 Herculis, is magnitude 5.5, showing that the comet has faded considerably in the past week. But it is now much higher in the sky and remains easily accessible until after 9 pm BST.
The ZWO Seestar50 smart telescope is now taking over from many conventional systems due to its rapid set-up time and ease of use. This image was obtained in three minutes at 19:45 by Cath Adams from Patshull, Staffordshire. ‘My society held a comet watch and we all struggled to find the comet. It seems to have dimmed quite a bit since I found it last week! My Seestar had it in its database and found it straight away so everyone was gathered round it to see where it was pointing.’