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On April 1st Michael Mattiazzo reported a probable comet in SWAN data with a position in Pegasus. I performed a search around the rough position on the morning of April 2 but didn’t find anything. Subsequently Qicheng Zhang found the comet in images he had taken using a 40mm refractor on April 2.51. This allowed Bill Gray to compute an ephemeris and Mattazzio then found a precovery image from March 30.22.
For now, this comet doesn’t have an official designation but you can get an ephemeris from here:
https://www.projectpluto.com/swan.htm
I imaged it this morning from Chelmsford in bright twilight as it cleared the roof of my house. Image attached.
Michael Jaeger reports a total magnitude of 10.0.
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Nice coverage, Nick.
This is core Comet section work.
I see your astrometry (along with D15 and A71) extends the observational arc to about 7½ days.
Will it reach about 10th mag or similar?Richard
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 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.
Will do. Was up this morning at 4am to observe, but there was a lot of cloud from the N to E. Of course it had all cleared by 9am…David
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.
Captured this morning with my Seestar. Looking good!
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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.
That’s a great image of it. I tried to spot it this morning around 5am but I think the sky was too bright to capture it or see it using binoculars. Will continue to try for the next few days.
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.
Glad it now has a name.
4 am alarm failed to wake me this morning so was late going on duty. Brightening sky rapidly halted play. 14 min 50 sec of 10 sec subs with Seestar S50. Tail was much less visible than yeaterday but yesterday alarm woke me and managed nearly 25 minutes.
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Good news. C/2025 F2 (SWAN) is now in Seestar catalog. No Seestar star hopping for me tomorrow morning.
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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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Well alas total failure to see it on my part this morning. At 4am this morning, the sky was clear except for the NE horizon! by the time the region passed away form a chimney and out of the murk the sky was too light so I was unable to see it. I believe I may have seen it in binoculars, but the fact that it wasn’t obvious in my 80mm OG finder nor that obvious in binoculars makes me think it must be fainter than magnitude 8.
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.
I was lucky this morning as clouds and haze disappeared and my Seestar got a picture. Taken from Northern Denmark.
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Up at 2.30am, clear, drove 4 miles to get a low NE horizon, my Seestar’s view at 3.30am. A little frustrating!
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I got up early yesterday (9.4.25) before work and managed to get the attached. Pretty disappointing, and the tail very faint compared to other observations I’d seen online. Askkar 120 with 0.8x reducer and Canon 6D, this is about 12 minutes in total of the best subs captured between 03:17 (UT) and 03:54 (UT); there were lots of bad subs. 30 seconds each, ISO 400. Desaturated and inverted to allow me to see the tail.
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