While the recent outburst of Comet C/2025 R2 (SWAN) dazzled southern skywatchers, another icy traveler prepares for its own spectacle. Comet C/2025 A6 (Lemmon), discovered on January 3, 2025, by the Mount Lemmon Survey in Arizona, is steadily making its way toward the Sun and Earth.
What makes Comet Lemmon special is both its increasing brightness and its rarity: this non-periodic comet is a once-in-a-millennium visitor, returning from the far reaches of the Solar System on a long elliptical orbit of 1,350–1,400 years. If predictions hold, it could reach naked-eye brightness in late October, joining C/2025 R2 (SWAN) in the night sky. Even better, its closest approach coincides with a New Moon and the peak of the Orionid meteor shower, setting the stage for a truly unforgettable night of stargazing.
Latest Updates on Comet C/2025 A6 (Lemmon)
- Closest approach to Earth (perigee): October 21, 2025 (some reports cite October 20, depending on orbital rounding), at about 0.60 astronomical units (90 million km / 56 million miles).
- Closest approach to Sun (perihelion): November 8, 2025, at about 0.53 AU (79 million km / 49 million miles).
- Current brightness: Now at magnitude +7.8 and brighter than expected, though still below naked-eye visibility. Forecasts suggest it may reach a magnitude between +4 and +5 under dark skies by mid-to-late October, though comet brightness predictions remain uncertain.
- Prime viewing window: October 21 aligns with the New Moon, ensuring dark skies. Around the same time, Comet SWAN will also be near Earth while the Orionid meteor shower peaks, a perfect cosmic lineup!
Observing Tips
- When to look: Mid-October to early November is ideal for Northern Hemisphere observers. The comet will appear low in the western sky roughly 30 minutes after sunset.
- What equipment to use: It may be visible to the naked eye under dark skies, but binoculars or a small telescope will offer the best views of its coma and tail.
- What to expect: Recent images show a greenish coma. Watch for its distinct bluish ion tail.
- Where to find it: Around October 21, the comet will be near Arcturus in the constellation Boötes.
- Special viewing note: For observers north of about 48° latitude, the comet becomes circumpolar around October 10, meaning it will be visible all night.
- Additional tips: Choose a dark-sky location away from light pollution and ensure an unobstructed view of the western horizon, as the comet will sit low after dusk.
- SkyPortal Powered by SkySafari™ Mobile App: If you own a Celestron telescope, download the app for an interactive star map with up-to-date charts and magnitude estimates.
Comet C/2025 A6 (Lemmon) appears to be one of the most notable astronomical events of the year. Its closest approach closely coincides with comet C/2025 R2 (SWAN), a dark New Moon sky, and the Orionid meteor shower, creating an unusually favorable window for observation in late October. From the unaided eye to using your Celestron binoculars and telescopes, this once-in-a-millennium visitor will remind us just how beautiful and mysterious the universe truly is.