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Taking the recent astrometry I think the attached image from I79 this morning has correct identification of the components.
It looks like the main component and component B have pretty much gone now. Component D appeared recently and is faint. Component C has been around for a while and has recently brightened to the point that it is the most prominent part.
The comet doesn’t look very healthy though and I doubt if there will be much remaining to measure soon.
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The brightest component as of last night (Dec 6.95) seems to be close to the predicted position of the C fragment.
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As of tonight there is not much left. The brightest fragment is the one furthest down the tail. It looks as if this comet doesn’t have much life left in it.
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Yes, it is still there but it is getting a lot fainter and the sky tonight was very bright. My image from earlier attached. The fragments are still visible but the main component is around 3 mags fainter than it was a week ago.
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The weather at the Alnitak telescope in Spain has not been too good the last few nights but I did get an image of the comet from Chelmsford yesterday morning. The comet is now moving away from the Earth so the physical scale is getting smaller but fragments are still visible. I’ll be preparing a report for the February Journal so many thanks to everyone who has submitted images.
The latest images in the section archive are here:
https://britastro.org/cometobs/2025k1/thumbnails.html
Most of these are north up so you can see how the tail has rotated rapidly over the past few weeks as our viewing angle has changed.
C/2025 K1 continues to change night after night. Tonight’s (Nov 30.7) image attached. Our viewing angle has been changing rapidly and the tail has now rotated so that it is almost pointing due south. The fragment we saw a few days ago south and a little east of the brightest component is still there but much fainter and there is a definite extension north of the bight component.
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Here’s an image just taken from Chelmsford. It shows the nova at 18.3 unfiltered (ref Gaia G) in the blue circle.
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I’ve been away so I haven’t had a chance to do my nightly M31 patrols. I did get the 2023 eruption just after it was discovered though:
https://britastro.org/forums/topic/m31n-2008-12a-call-to-arms
so it is definitely available to small telescopes although it does fade very quickly. I’m back home now and it is clear here at the moment.
Sheridan – It depends on exactly what you want to do and what focal length of optics you’ve got. A lot of current CMOS cameras have small pixels so that might not be ideal if you have a very long FL although you can always bin them. Most are now based on Sony Starvis sensors which are very good. I use ZWO cameras so I would suggest having a look at what they have available. The 585MC would be a good place to start. It can be used for deep sky and planetary, has pretty high frame rates but is also able to take the longer exposures you would need to show deep sky objects in real time. The ZWO software suite includes software that can real-time stack images too.
As of this morning (Nov 27.2) the C fragment is no longer measurable in the I79 images.
Steve – certainly looks like you got A and C with the Seestar even though you needed 3 hours exposure to get a reasonable SNR. It is a 50mm aperture refractor after all!
The HST image in the paper with Helen as co-author mentioned above is very impressive too.
Courtesy of the BAA/Comet Chasers group I have processed some data obtained earlier today from the 2.0-m f/5.2 RC Foulkes Telescope North (F65). This has an image scale of 0.27″/pix. This image is resampled by a factor of 2 and is 2.3 arcmin square. It is a stack of 3x10s images taken at half the comet’s offset rate.
It shows a separate, faint apparent fragment just ahead of C and an elongated bright area behind A. It also confirms the demise of fragment B.
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This morning’s (Nov 22.22) image from the Alnitak telescope in Spain shows that component B has become very diffuse and it looks as if it is not long for this world. The astrometric residuals for B are now large and this reflects the fact that it doesn’t have a definite centroid any more.
The astrometric residuals for component A are generally small and they fit the previous orbit well, so we presume that this is the original nucleus, but the astrometry from this morning shows significant residuals. This component has also brightened significantly over the past few mornings. This may be a sign of further fragmentation so please keep observing this comet as frequently as possible.
This is why comets are so much fun. You never quite know what to expect when you observe them!
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I assume that most of the alien spacecraft nutters have given up hope now given that the comet has not changed course and there is no sign of their attack ships having arrived at Earth. In fact, I wonder why, if the aliens are so clever, that they seem to be totally useless at stealth technology. 3I/Atlas is pretty bright and hard to miss. Everyone is looking at it. The Klingons could teach them a thing or two about cloaking tech.
As of this morning fragment C is the brightest component.
https://britastro.org/observations/observation.php?id=20251117_052037_e18a08602a3cf34b
Robin. Yes. There are three components now. Attached is an image I processed from yesterday using data obtained by the Comet Chasers group. Component C is quite bright and would merge with the main component if seeing or resolution is poor. As of yesterday morning it was around 4 arcsec from the main component.
Z17 is a Planewave Deltarho 350 with an IMX455 sensor at 2300m Teide so a rather nice setup!
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Alex – Yes, I should have plenty of material for the Christmas sky notes what with all this alien nonsense and the reports of spectacular meteor storms and auroral displays that appear regularly in the media.
Conventional modelling of the dust tail of a comet assumes that the dust grains are small and emitted from the nucleus in all directions at low velocity. Solar radiation pressure is then sufficient to accelerate the grains in the anti-Sun direction to form the dust tail. In the case of 3I one explanation for the “anti-tail” is that some of the dust grains are large and that they are emitted preferentially in the sunward direction at a higher velocity. It then takes more time for the solar radiation pressure to turn them around and push them back in the anti-solar direction.
This mechanism was postulated for the anti-tail of C/2014 UN271 in this paper by Farnham et al:
https://iopscience.iop.org/article/10.3847/PSJ/ac323d
The attached graphic is figure 7 of that paper. It shows modelled dust tail syndynes for different particle sizes and emission velocities and it demonstrates how an anti-tail can form in these circumstances.
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Denis,
This is worth a read:
https://sites.psu.edu/astrowright/2025/09/29/3i-atlass-anti-tail-isnt-unique/
After debunking a load of Loeb junk it explains that the anti-tail in this case is related to relatively massive dust grains that don’t get accelerated backwards into the tail. It references the famous LSST paper that has a zillion (I exaggerate slightly) authors:
Loeb has linked to an image in our gallery:
See the second link in the first sentence. I’m not sure what point Loeb is trying to make in the subsequent text but Michael and Frank’s image of the tails of 3I is very impressive.
