Home=Current Comets: C/2025 T1
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An object of magnitude 16, discovered on Oct. 11, 2025 by the ATLAS project in the constellation Ursa Major, revealed its cometary nature during follow-up observations. Comet C/2025 T1 (ATLAS) showed a coma of 1.5-2.0' diameter with a total magnitude of 14.0 and a short, towards SSW pointing tail. The comet will pass perihelion at a solar distance of 1.11 AU on Dec. 2, 2025 and could reach magnitude 12.5 in mid-November (at perigee) (CBET 5624). It will remain brighter than 16 mag until the end of February 2026. During this period it will move through the constellations Ursa Major, Draco, Hercules (maximum brightness), Lyra, Vulpecula (perihelion), Sagitta, Aquila, Aquarius and Capricorn. From locations in Central Europe it can be seen in the morning sky until mid-November and in the evening sky until mid-January (then at about 14.5 mag), switching from the morning to the evening sky at the end of October.
At the beginning of November 2025 36 observations from 19 observers can be used for a rather preliminary analysis. These indicate a steep increase in activity (the comet brightened from 13.5 mag to 10.0 mag within the first three weeks), which could be the result of an outburst. The estimates indicate the following brightness parameters
m0 = 6.5 mag / n = 18,which yield a peak brightness of 8.8 mag at the end of November 2025. However, this prediction is still subject to considerable uncertainty, and further observations will most likely reduce the determined activity parameter.
Total Brightness and Coma Diameter
In parallel to the rapid brightening the coma diameter increased rapidly from 2' (140,000 km) to 5' (240,000 km). The coma appears rather diffuse (DC 3). No tail has been detected so far.Andreas Kammerer
