C/2025 A6 (Lemmon) is a non-periodic comet discovered by the Mount Lemmon Survey in images obtained on January 3, 2025. Its orbital period is about 1,350 years and will pass perihelion on November 8, 2025, when it is 0.53 AU (79 million km) from the Sun. This perihelion passage will reduce the orbital period to about 1,155 years. It reached its closest point to Earth on October 21, 2025, and may be faintly visible to the naked eye at 42 degrees from the Sun after sunset. As of September 12, 2025, the comet had an apparent magnitude of about 9.4.

C/2025 A6 (Lemmon) was first identified as an asteroid with an apparent magnitude of about 21.5 while 4.5 AU from the Sun in pre-discovery images taken by Pan-STARRS on November 12, 2024. The object was found to have a very condensed coma, 2.2 arcseconds in diameter. A short tail, two arcseconds long, is seen in images from February 21, 2025. At discovery, the comet was expected to reach only an apparent magnitude of 10, but is now predicted to reach an apparent magnitude of 4, making it 250 times brighter than previously thought.

The astronomical unit (symbol: au or AU) is a unit of distance used in astronomy to measure distances within the solar system. It corresponds to the average distance between the Earth and the Sun, or approximately 150 million kilometers.

Current Passage in October 2025

Key Date : On October 21, 2025, the comet reached its closest point to Earth.

Observation Period : It was visible in the night sky until the end of October 2025, in conjunction with Comet Swan (C/2025 R2).

Visibility : It was potentially visible to the naked eye or, more likely, with binoculars.

Next Passage
It will be very late : This pass in October 2025 is unique, as the comet has an orbital period of approximately 1,155 years.

Return Date : It will take more than a thousand years for its return visit.

Set up

Skywatcher Esprit 100ED on EQ6 R Pro Mount
ASI2600 MC Pro camera for imaging
ASI120 mini camera for guiding via Off Axis Guider Zwo
UV/IR Cut anti pollution Filter
Control via ASIAIR PLUS
Gain (ISO) : 101
Camera cooling : -10°C

Preprocessing and Processing with Pixinsight

The session

Lemmon was taken beginning of October 2025 in 2 nights
Total integration : 2 hours for both images.

The galaxy NGC 3184 is also visible (Above the comet's nucleus)

This image was taken on the second night of October 2025.

Astrometry : Annotated Image

Clear Sky !

C/2025 A6 (Comet Lemmon)

Astrophotography in video