Orwell Astronomical Society (Ipswich)
Comet C/2025 K1 (ATLAS), 18-21 November 2025
Comet C/2025 K1 (ATLAS) was discovered on 24 May 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS). It has come directly from the Oort cloud. Perihelion was relatively close to the Sun (0.3 AU) and the comet was not expected to survive perihelion passage; it did, however, and became visible again in mid-October. As of mid-November 2025, the comet is visible in Ursa Major and the nucleus has broken into multiple fragments.
The comet was travelling through the sky at some 9" per minute, forcing the use of short exposures to avoid blurring detail. The image below shows the three main components of the nucleus.
I awoke at 4.00am to find a clear sky. It was cold and the main mirror and corrector plate of my telescope were both covered with a layer of condensation.
The image and video below show the three components of the nucleus. The separation of the two outer components is approximately 17.1", compared with approximately 12.4" at the time of my last observation (above) two days ago. The central component has faded and now all three are similar in brightness.
The comet is at high altitude in the early morning and continues to show interesting developments. The image below show thre three components of the nucleus, the outer components now approximatley 19.1" apart. Yesterday (see above) the three were of very similar brightness but today the central component had faded.
The following video shows the motion of the comet across the sky.
Nigel Evans