Home=Current Comets: C/2025 R2
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On Sep. 10, 2025, Vladimir Bezugly (Ukraine) discovered an object in the publicly available SWAN images which he assumed could be a comet. He informed the comet community, and finally, on Sep. 12, M. Masek managed to capture an image of the comet with a 135mm telephoto lens from Cerro Paranal. The comet, located in the constellation Virgo, was of magnitude 7.5, showing a coma short of 4' and a 2.8° tail in p.a. 114°. During the following days other observers confirmed these values. Comet C/2025 R2 (SWAN) passed perihelion at a solar distance of 0.50 AU on Sep. 12. The comet will approach Earth to within 0.26 AU (Oct. 19), expected to reach magnitude 6.0 at those days (CBET 5606). If it experiences an average brightness development the comet should be brighter than 16.0 mag until the end of March 2026. During this period it will move through the constellations Libra, Scorpius, Ophiuchus, Serpens, Scutum (perigee), Aquila, Aquarius, Pisces and Aries. From mid-European locations it will appear above the southwestern evening horizon around Oct. 10, then quickly gaining altitude until the first week of November. It will reach greatest altitudes (around 50°) in mid-January 2026, thereafter descending towards the horizon. The comet has an orbital period of 680 years (CBET 5618).
During the second half of October 2025 this comet was easily visible with binoculars, although the weather was not very cooperative. Based on 381 observations by 65 observers (until the start of November 2025) the brightness parameters are
m0 = 9.0 mag / n = 2.3,resulting in a peak brightness of 5.8 mag on Oct. 15, 2025. However, the absolute magnitude is only slightly above the Bortle limit. Therefore it came as no great surprise when images taken with the TTT3 telescope on Nov. 2 showed a fragment next to the main component (ATel 17469). By Nov. 10 the comet had faded to 9.0 mag – primarily as a result of the rapidly increasing distance from Earth after its closest approach.
Total Brightness and Coma Diameter
The apparent coma diameter increased rapidly from 2' in mid-September to the maximum of 17' around Oct. 20. Thereafter it declined in a similar way, measuring just 6' on Nov. 10. In absolute terms the coma expanded from 100,000 km at the start of the apparition to the maximum of 200,000 km around Oct. 20, thereafter shrinking, measuring 150,000 km by Nov. 10. The coma became steadily more diffuse. While in mid-September the coma showed a degree of condensation of DC 7, this decreased to DC 2-3 by Nov. 10. A tail was observed from mid-September to at least early November, reaching a maximum visual length of 1.0° around Sep. 25, which corresponds to an absolute length of 1.5 mio. km (it could be traced up to short of 3° on CCD images). The orientation of the tail changed only slightly from ESE to ENE.The further development is uncertain due to the observed fragmentation. If the brightness development observed so far continues the comet would fade to about 14.0 mag by mid-February 2026. The comet is moving from the constellation Pisces to the constellation Aries, making it an object of the evening sky.
Andreas Kammerer
