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I got my first image of this comet from Chelmsford this evening when it was around 5 deg up in bright twilight. It is now moving north and the circumstances get better for the UK over the next week. It is currently around mag 6.
https://britastro.org/observations/observation.php?id=20251008_225616_f9ba3c0ba77b5e84
It was cloudy here in Chelmsford so I’ll I got was the double flash on the cloud. The FRIPON network of all-sky cameras picked it up at 19:10:54 UTC.
James – If you really are that lazy (and I’m sure you are not) then I’m surprised that you have the energy to make the observations in the first place! Each section will have its own way of accepting observations and the basic rules are pretty easy to follow. You don’t need to remember them, you can use the wonderful invention of writing to make notes and set up a procedure to follow for each object. It will then only take a few minutes of your time.
I have never dismissed people as “not serious observers” if they don’t want to do this. It is personal choice and the quality of the images in the gallery is fantastic whether or not you want to submit them to the section. I would like to encourage you to do so but you need to follow our rules. That means making sure that all of the key observation details are recorded and using a filename which is compatible with our requirements. One of the things that makes the BAA special is that we do try to encourage people to think of the science behind their observations. For me, that greatly increases my enjoyment of the hobby. It will be different for others.
As Dominic says, we could spend time trying to make the gallery into a source for the section archive but there are other priorities for our website developers at the moment and this would still mean that many images would not be imported since they lack critical details.
As a compromise, I’m currently discussing with Denis whether he is willing to manually collect data from the gallery that has appropriate metadata and reformat it so that it can be put in the archive. I’ll let you know the outcome of that discussion.
Good points James but I think the gallery and the section archive serve different purposes and it would be difficult, and probably not very effective, to combine the two. The gallery is a great way to share images with members and others but the section archive is our permanent record of observations. It may be frustrating that each section has a different way of naming files but that is the world as it is and it really isn’t that difficult to follow the filenaming rules when submitting images.
Given the amount of effort required to make the observation, both in terms of obtaining the data and processing it, it surprises me that even some of the world’s best comet imagers can’t spend a few more minutes to add key details like equipment, exposure time, duration, orientation and field-of-view. I know that analysts can often derive these by plate-solving but sometimes that is not possible and they have more than enough to do anyway. Also, C/2025 A6 (Lemmon) has demonstrated again how dynamic comet tails are on multiple scales so accurate information is critical to making the best use of images.
I’m very grateful for all of the images that the section receives but a little more work on behalf of the observer would make many of them much more valuable in the long term.
Nick.
I guess if you keep predicting an eruption “in a few months” you are likely to be right eventually, c.f. the end of the world…
That is great news. I know how much hard work has been going on in the background and this is an excellent result.
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.
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.
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.
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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
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Nick – For your 30 min stack the length of the trails in your image is around 50 arcsec. The Hubble image that Denis linked shows a short (approx 4 arcsec) and very faint extension in PA 300 or so. I doubt that you are detecting the coma yet but your image is definitely of high quality.
The HST constraints on nucleus diameter are interesting. Details are in the ArXiv paper here: https://arxiv.org/pdf/2508.02934.
Ian,
It is worth submitting magnitude estimates to COBS if you can. There is a lot of scatter on the current estimates but they suggest that the comet might reach mag 14 in November as it comes out from solar conjunction.
James,
The maths is simple but probably not very useful for your application.
Tensile strength is measured in Pascals and a Pascal is a Newton per metre squared. If a rod has tensile strength T [N/m^2] and diameter d [m] then it will support a weight which is a product of its tensile strength and area, i.e. W = T * pi * d^2 / 4 [N]. The material will permanently deform long before it breaks.
Taking your example of T = 600MPa and d = 0.004m then W is around 7500 N which corresponds to a mass of 750 kg at the Earth’s surface.
I got the comet with a RedCat 51 last night. This has the same aperture as a Seestar 50 so it should be in range of those now although I had the advantage of a cooled camera and a dark sky at 2100 m on La Palma!
https://britastro.org/observations/observation.php?id=20250724_150857_253c99e511be2b41
The magnitude estimate on that image is probably rubbish since it is contaminated by stars but it is brighter than I expected.
Nick – It is definitely worth trying to get some photometry if you can. You could use Sloan r’ mags for your long-pass data and you would at least be able to see if you are consistent from night to night.
Paul – I’m pretty sure that the scatter is due to faint stars in the aperture since this is a very crowded field. I think it is far to early to say anything about the lightcurve of this object but the more observations the better. I have used DAOPHOT and it can be very good but I’ve not been able to get it to work reliably with moving objects.
I’ve been doing some astrometry on 3I/ATLAS and have been surprised how much scatter in the magnitude that I’m getting day to day. The plot of magnitudes from MPC astrometry data also shows a huge scatter. This data doesn’t have a consistent photometry aperture or filtering but, for most observers at the moment 3I/ATLAS is a point source so it is surprising. The scatter may be due to measurement errors in the crowded star field but it is worth making estimates of the magnitude if you can.
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