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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.
I use a cooled camera (an ASI1600MM) with the cooling off to image the Sun with short exposures in the daytime and with the cooling on to image the deep sky with long exposures at night. Apart from the extra weight of the Peltier, heatsink and fan there are no disadvantages that I am aware of. Regarding David’s point about frosting up when the cooling is on, none of the more recent ZWO cameras that I own have suffered from this. It was a common problem many years ago but modern cameras are better designed with smaller, well sealed, chambers and, sometimes, window heaters.
David. That’s a great image. This is perfect opportunity for Seestar (and other smart scope owners) to do some comet science by estimating the comet’s total magnitude from the green pixels of their images.
As you’ve noticed the MPC ephemeris for this object is way off. Bill Gray’s online ephemeris uses the same astrometry but gets the correct result and I recommend that you use that for now.
https://projectpluto.com/neocp2/mpecs/SWAN25F.htm
This object is still on the PCCP a week after discovery and it has not yet received a formal designation even though there is tons of astrometry and no question about its cometary nature. It is currently around magnitude 8 and, as your image shows, has a nice, but faint, ion tail.
The ephemeris in the third post above is still pretty good but while the comet is on the PCCP you can get an ephemeris from:
https://www.minorplanetcenter.net/iau/NEO/pccp_tabular.html
Just select SWAN25F.
I imaged the comet from Chelmsford again this morning (April 6) and it was considerably brighter than yesterday. I get the following total magnitudes and coma diameters with comphot using a 51mm, f/4.9 refr. + ASI2600MC. Green channel vs Gaia G DR3:
2025 April 5.157 9.6 2.3′
2025 April 6.150 8.0 3.8′Transparency was probably a bit better this morning but conditions and time were similar.
Interesting behaviour so please observe this comet if you can and submit magnitude estimates. It is still on the PCCP so no official designation yet but there is now pre-discovery astrometry from Panstarrs going back to early September.
Thanks Richard. Tracking it down was a good team effort. It is currently on the PCCP but it is most definitely a comet!
It is well placed for us to follow from the UK. It is moving north but the elongation is decreasing as the Sun moves north too. The current orbit is based on astrometry from March 26 – April 3 and it may change a bit. The orbit is parabolic and the comet reaches perihelion on May 1 at a distance of 0.33 au. For us it moves slowly northwards in the morning sky, passing under the pole in late April and then becoming an evening object. It should brighten by a couple of magnitudes from where it is at the moment.
I wonder if T CrB will go into history as the variable star equivalent of comet C/1973 E1 (Kohoutek)?
I wish I’d seen it. One of the disadvantages of observing from indoors!
Alex – The whole point of the propellant dump was to avoid creation of space junk. It ensures that the stage did not break up due to tank overpressure and, in any case, the stage de-orbited into the Indian Ocean.
I have a CGE which, I think, is similar to the CGEM and get these messages every now and again. It is usually the RA/Dec cables between the mount controller and the motors which are pretty rubbish. If you disconnect/reconnect the connectors it often works or give them a spray with some switch cleaner like Servisol. I think it is unlikely to be the main board. Much more likely to be a bad connection somewhere.
