SWAN25B

[Mr Owen Michael Brazell]

Surprised there has been no mention yet of the new comet SWAN25B. I know it is only visible to southern members at the moment but if it lasts will come north.

[Paul Anthony Brierley]

Hi Owen,

I only read about the discovery after reading the latest newsletter from SpaceWeather.com
It will be interesting to see if it survives. If it does. Then it will certainly be worth looking out for when it appears in our skies.

[Nick James]

This comet was first noted in SWAN data by Vladimir Bezugly on September 11. We now have a 40 hour arc of decent astrometry from southern hemisphere sites and, forcing e=1, I get a perihelion of 0.50 au on Sept 10 (see the elements attached from FINDORB). This orbit is still pretty unreliable but it indicates that the comet will make a close approach to the Earth on October 17 when it is at a decent elongation (76 deg). How bright it will be at that time is anybody’s guess.

I’ve also just updated the item on C/2025 A6 and that is looking promising now, so October could be an exciting month for comet observers:

https://britastro.org/section_news_item/c-2025-a6-lemmon

Attachments:

1. 

   SWAN25B_elems.png
   

[Grant Privett]

Thanks for the plots. Already looking forward to it!

At the time its in Bootes. Good timing for T CrB to finally go bang.

[Nick James]

These plots are based on the current, rather uncertain orbit and the predicted magnitude is just a guess. The observability plot shows the elevation of the comet at evening nautical twilight for various latitudes. At 50N we don’t get a chance until early October but it will be a good target for observers with access to telescopes further south.

The elongation plot shows that it has been within 30 deg of the Sun since late July. That fact that it wasn’t picked up by surveys earlier this year when it was at a large elongation implies that it has brightened rapidly and so it will possibly fade rapidly as well.

I’ll update the plots when we have a bit more astrometry.

Attachments:

1. 

   evening.png
   

2. 

   elong.png
   

[Robin Leadbeater]

Nick James wrote:

I’ve also just updated the item on C/2025 A6

month typo in the last line on that page

(we really need a PM button on this forum)

• This reply was modified 3 weeks, 2 days ago by Robin Leadbeater.

[Nick James]

Robin – Thanks. That is corrected now.

[Nick James]

This comet has been formally designated C/2025 R2 (SWAN) on CBET 5606. The attached chart is based on the latest orbit but the comet won’t be observable from the UK until early October by which time it is likely to have faded considerably.

Attachments:

1. 2025r2.pdf

[Nick James]

My image using a remote telescope in Namibia (FSQ106 + IMX455) shows a 4 deg tail and the total magnitude using comphot is 7.4. A nice surprise comet even though it is not currently visible from the UK.

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