Overview
- On Saturday, Oct. 25, Comet Lemmon (C/2025 A6) is best sought low in the northwest near Arcturus as it moves into Serpens, while Comet SWAN (C/2025 R2) sits in the southwest near the Summer Triangle, roughly 90 minutes after sunset.
- Binoculars (8x42 or 10x50) are recommended, with each comet appearing as a diffuse, fuzzy patch; dark-sky locations and finder apps like Stellarium or SkySafari improve the odds.
- Viewing conditions will deteriorate rapidly as the waxing crescent brightens through the coming days, shrinking the short post-sunset window despite both comets still being technically observable.
- Comet Lemmon, discovered Jan. 3, 2025 by the Mount Lemmon Survey, reaches perihelion on Nov. 8 and is an infrequent visitor last seen around AD 875, with return estimates near 1,150 to 1,300 years.
- Comet SWAN, identified Sept. 11, 2025 in SOHO SWAN data, follows a far longer orbit of roughly 20,000 years and is generally fainter than Lemmon this weekend.