Comet 2025/A6 (Lemmon) Oct.5

On the night of October 5th, 2025, I captured this image of Comet C/2025 A6 (Lemmon) as it glided across the starry sky. This comet, discovered earlier in 2025 by the Mount Lemmon Survey in Arizona, has been steadily brightening and is now becoming a fascinating target for both amateur and professional astronomers.

Today it’s been crossing a rich starfield with Tania Australis and Tania Borealis stars as the most prominent stars in the image. The two make a lovely contrast, Tania Borealis a white class A subgiant, Australis a fairly rare (for naked eye stars) red class M (M0) giant. Tania Australis shines at mid third magnitude (3.05) from a distance of 250 light years (double the distance of Borealis, the two only a line-of-sight coincidence).

In the image, you can clearly see the comet’s greenish coma, a result of diatomic carbon (C₂) fluorescing in sunlight, and its developing tail extending away from the Sun. These features make “Lemmon” a striking reminder of the icy wanderers that visit the inner Solar System from the distant Oort Cloud.

Observing comets like Lemmon requires a dark sky, and October nights provide excellent opportunities to follow its evolution. Over the coming weeks, the comet will continue to shift position against the background stars, gradually changing in brightness and appearance.

Image taken on October 5th, 2025 – Prades (Catalonia, Spain).

The full image covers an area of 2º16′ x 1º43′ at a resolution of 1.46″/pixel.