Comet C/2025 A6 (Lemmon)

We have been fortunate to have several comets grace our skies recently and the brightest of these has been comet Lemmon. This comet was discovered by David Fuls on the 3rd January 2025 during a survey at Mount Lemmon Observatory. During the intervening months it has significantly brightened and around the end of the October it reached its maximum luminosity of about 4th magnitude. On October 25th I was fortunate enough to get a good view of the comet when we had some clear skies in the early evening. At 19:41 UT I took this wide-field view:-

 

The comet has been marked on the image with green lines (the image can be better viewed by clicking on it). It sits in the constellation of Serpens (Caput - i.e. the head) and below the distinctive crown of the constellation of Corona Borealis. The field of view this image is approximately 64x46 degrees. I used a Sony RX100 camera with an exposure of 10s at f/1.8 (ISO 1600). I took another image with the same camera and pointing in the same direction but used a focal length of 20mm rather than 10mm:-

 

This was again a 10s exposure at ISO1600 but this time at f/3.5. The comet has again been marked. Looking closely at this image you can see that the comet tail extends quite a long way up towards the crown of Corona Borealis (some 12 degrees). The field of view of this image is approximately 36x25 degrees.

Finally, I wanted to look at how the comet's position compared with ephemeris predictions. For this I took a chart produced by Nick James at the BAA and overlaid it on my first image that I took:-

 

It was difficult getting the orientation and scaling correct but by making sure that the stars near the comet overlap reasonably well, you can see that the comet does indeed sit on the predicted path. As the observation time was 19:41 UT on the 25th which is 0.820 of the day, you can see that the comet is about the right distance along the track towards the 26th tick mark from the 25th tick mark (taking that the tick marks are for midnight UT).

The comet is now beginning to fade and passed perihelion on the 7th November. 

All text and images © Duncan Hale-Sutton 2025