2025 August 25

C/2025 A6 (Lemmon)

Nick James

C/2025 A6 (Lemmon) was discovered as an apparently asteroidal object on 2025 January 3.342 in images taken by David Fuls using the 1.5-m reflector of the Mt Lemmon Survey. It was originally placed on the PCCP as CCNG6P2. Follow-up images showed the object to be cometary and it was announced as C/2025 A6 (Lemmon) on CBET 5508.

The comet comes to a perihelion of 0.53 au on 2025 November 8 and the orbit is periodic with a period of a few thousand years. It has recently reappeared after solar conjunction and it is rather brighter than expected although we don’t yet have enough data to predict how bright it will get in early November. It might reach magnitude 5 or brighter if the current brightening is sustained. Please observe it if you can and make magnitude estimates to submit to COBS.

The comet is currently a morning object but it will move into the evening sky in mid-October. Those of us at higher northern latitudes are quite favoured as shown in the plots below. These show the (very uncertain) predicted magnitude based on H=7.9, G=3.2 and the (very accurate) altitude of the comet above the western (evening) and eastern (morning) horizons when the Sun is 15 degrees down.

The Moon is new on October 21 and full on November 5th so conditions are good for when the comet will be at its brightest and furthest above the horizon.

Current images are in the section archive here.