2025 October 14
Two comets in the evening sky
Unusually, there are two bright comets visible in the evening sky at the moment. One of them, C/2025 A6 (Lemmon) has been visible in the morning sky for several months. It is currently around 5th magnitude and brightening and we expect that it will reach 3rd magnitude at its brightest later this month. The other comet, C/2025 R2 (SWAN), has been a southern hemisphere object and it will remain at a negative declination, but it is now visible from the UK. It is currently around 6th magnitude and will probably fade through the rest of October. Both comets have long, faint, ion tails and C/2025 A6 looks to be developing a more prominent dust tail.
The easiest comet to see will be C/2025 A6 as it moves through Canes Venatici into Bootes and then Serpens through the rest of October. New moon is on October 21 so, if the weather cooperates, we should have the opportunity to see it reasonably high up in a dark sky. Wide-angle images show that that the ion tail is already multiple degrees long and narrow-angle images show a lot of detail in the coma and inner tail. The BAA image archive for C/2025 A6 is here.
Comet C/2025 R2 will be more of a challenge. It remains a southern hemisphere object but it is rising higher in the SW evening sky. Through October it moves from Ophiuchus into southern Aquila. It is currently around 6th magnitude and it will fade to around mag 7 by the end of October. The BAA image archive for C/2025 R2 is here.
Astrometry and photometry of both comets is important. Submit astrometry to the MPC and total magnitudes to COBS as normal. The section also collects 9 arcsec radius photometry. Send this to cometobs@britastro.org or contact me for advice. Images can be submitted to the section using the procedure described here.
Good luck with observing both of these comets. Finder charts for both comets are below and here as PDFs for C/2025 A6 and C/2025 R2. Details of how to observe comets are included in the section Observing Guide. Let’s hope that the weather cooperates.
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