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This interesting paper has jus been posted on Archiv:
https://arxiv.org/pdf/2506.11217
The authors consider the potential effect of a lunar impact of 2024 YR4 on 2032 December 22. They conclude that it could temporarily increase the flux of mm sized meteoroids in near-Earth space by several orders of magnitude. This could be bad news for spacecraft in low-earth orbit but might give us a nice meteor shower.
The probability of a lunar impact is currently around 4% and the high end of their flux predictions require some relatively unlikely alignments to happen but it is definitely an interesting read.
The latest prediction from Marco Langbroek is that re-entry will occur around 06:30 UTC tomorrow, May 10, with an uncertainty of +/- 4.1 hr:
https://sattrackcam.blogspot.com/2025/04/kosmos-842-descent-craft-reentry.html
The latest TLE from space-trak (dated March 9.655) has perigee down to 127 km. The spacecraft has passes over the UK on May 10 as follows (times are UTC):
04:34 – Low elevation in the southeast.
06:05 – Almost overhead
07:36 – Almost overhead
09:06 – Low in the southwest.All of these are in daylight so if it does re-enter over the UK we are unlikely to see it but, if the sky is clear it might be worth looking when it comes over.
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Unfortunately we don’t have any night-time passes of this spacecraft coming up.
This page will get updated as the TLEs get updated:
https://aerospace.org/reentries/6073
The current re-entry prediction is 2025 May 10 04:42 UTC +/- 19 hours.
The conditions were slightly better low to my northwest this evening and the comet is more obvious in this stack:
https://nickdjames.com/Comets/2025/2025F2/2025f2_20250429_203939_ndj.jpg
My image of this nebula at 0.56 arcsec/pix taken this morning (April 29.06) shows quite a bit of detail in the brighter part of the nebula. Certainly an interesting object to follow.
https://britastro.org/observations/userimg/20250429_202133_f7c854744716.jpg
I got a possible detection of the remnants of this comet last night (April 28.86) from Chelmsford, low in the bright evening twilight.
https://britastro.org/observations/observation.php?id=20250429_063941_2990db2ceeed4e3a
Yes, the ion tail is straightforward since it consists of ions accelerated away from the coma entrained in the solar wind and so it extends radially along the anti-Sun vector. That is easy to calculate.
The dust tail is an orbital mechanics problem. Each dust grain leaves the nucleus at a particular velocity and then it gets accelerated, mainly by solar radiation pressure. The acceleration depends on the mass of the grain and its cross sectional area. Because of this acceleration, each grain moves in a slightly different orbit to the nucleus but the difference in velocities is relatively small and so the grains spread out from the nucleus in the comet’s orbital plane. There are some good online demonstrations of how this is modelled:
https://www.comet-toolbox.com/FP.html
https://hdr-astrophotography.com/comet-tails-simulations/One of the most spectacular dust tails of recent times was that of C/2006 P1 (McNaught):
https://britastro.org/cometobs/2006p1/thumbnails.html
A detailed description of how that was modelled is here:
https://www.sciencedirect.com/science/article/pii/S0019103518301192
Last night (April 21/22) was clear in Chelmsford and I got 102 single station Lyrids along with 45 sporadics, 5 alpha Virginids and 2 eta Aquarids. As expected activity peaked in the early morning hours with events every few minutes from 0300 UT to dawn.
Peter Carson managed to image C/2025 F2 (SWAN) from Spain on 2025 April 21.19. His image shows a diffuse, elongated, coma with no distinct photocentre and a brighter bar of material in PA 330 degrees.
https://britastro.org/observations/observation.php?id=20250421_202852_3fb2d1e648d24ca4
The ephemeris position is at the head of the bright bar so this consists of dust that has flowed tailward from the disrupted nucleus.
The comet’s orbit implies that this is a dynamically old object so it has previously survived perihelion. It wasn’t so lucky this time.
I’m not able to get onto the comet with my main telescope until it clears my house roof, by which time the sky is very bright, but here is an image from this morning (April 18.17). There is apparently no distinct photocentre any more.
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Yes, it does look very much as if this comet has expired. There are not many recent magnitudes on COBS but it seems to have stalled at around 8th magnitude and then faded. I haven’t managed to observe it for a few days due to the weather.
Grant – Are you an hour out? The sky was hardly dark at 20:00 UTC and my cameras show the aurora becoming active around 21:08 UTC.
I have a quite extensive red aurora visible on one of my monitoring cameras in Chelmsford now (April 16, 21:11 UTC).
Indeed, a brilliant weekend. My first for three years since the last two clashed with eclipses. Sparsholt is a lovely location and the food and lectures were great as always. It was great to meet up with many old friends and with new people that I had corresponded with but had not yet met. Many thanks to everyone involved in the organisation. You did a wonderful job.
There was some concern that we would not get through the two kegs of ale that the bar had brought in for the weekend. They really had no need to worry!
This comet appears to be fading. I imaged it this morning (April 11.14) and I get a total magnitude of 9.6 and coma diameter of 2.3′ using comphot on the green pixels vs Gaia DR3. My last measurement was on April 9.14 when I got mag 8.6 and 3.0′. Some of this will be the brighter sky due to the Moon but the comet is also fainter in my 9 arcsec aperture photometry.
The attached plot shows 9 arcsec photometry from myself, Denis Buczynski and Peter Carson. Shortly after discovery the magnitude rose rapidly but it is now fading. Total magnitudes are shown on the COBS lightcurve here:
There is a huge amount of scatter on these from different observers. To see a trend you need to look at the results from a single observer using the same equipment and method. Mine are here:
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Paul – Thanks for trying. No chance here in Chelmsford this morning (April 10). Cloud streamed in from the North Sea about midnight.
It will be worth trying from Winchester this weekend although this will involve getting up early which may not be popular! The Moon is now a problem too. The latest estimates indicate that the comet is around mag 8.5 having faded a bit over the last couple of days.
Yes, the comet seems to have faded compared to previous days, both the total magnitude and the nuclear magnitude are fainter this morning. I had a total magnitude of 8.1 on the morning of the 7th, but only 8.6 this morning. The conditions were similar. My image from this morning, with the same aperture as your Seestar but a bigger sensor hardly shows the tail at all.
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This comet has been designated C/2025 F2 (SWAN) on CBET 5538.
http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET005538.txt
A similar designation to C/2020 F3 (NEOWISE) which was also discovered in spacecraft data, came out of nowhere and put on a good show in the summer of 2020. This will not be anywhere near as impressive (probably) but it should be a good binocular object.
