What Is Comet Lemmon and Why It’s Newsworthy
Comet Lemmon, officially designated C/2025 A6 (Lemmon) and also known as comet A6, is a long‑period visitor from the outer edges of the solar system. First discovered on Jan. 3, 2025 by the Mount Lemmon Survey near Tucson, Arizona, this icy wanderer is making a rare, once‑in‑1,350‑year swing around the sun. As it travels toward Earth, its close approach this week will bring it within 89.2 million kilometers (55.4 million miles) of our planet—an ideal setup for binocular observers in the Northern Hemisphere.
In simple terms: think of a bluish, diffuse patch with a tail that points away from the Sun. With careful observing, Comet Lemmon becomes a tangible beacon in the night sky even as it remains faint enough to require optical aids for most skywatchers.
Visibility: Where and When to Look
Comet Lemmon will be most accessible from the Northwest to Northeast during the early evening and just before dawn. In the days ahead, it will move from about 106 million to 91 million kilometers from Earth, gradually brightening as it approaches perihelion. By Tuesday, Oct. 21, its distance will be around 89 million kilometers, which coincides with notable celestial events.
The comet will be near the Big Dipper, a guiding landmark for observers. Since Ursa Major is circumpolar for many northern observers, it remains a persistent feature in the night sky, though it sits low on the horizon in autumn’s early hours. The best viewing window typically opens about 90 minutes after sunset for roughly 30 minutes, and another window can occur about 90 minutes before sunrise for early risers.
Tip: Check local sunset and sunrise times for your location and aim for a dark site with minimal light pollution to maximize contrast against a dark sky.
How Bright Will It Be?
Current measurements place Comet Lemmon around magnitude +5.2, which is at the edge of naked‑eye visibility under superbly dark skies. Realistically, most observers will need binoculars to clearly resolve its diffuse, fuzzy appearance. A large, steady pair of binoculars will reveal the coma (the head of the comet) and a bluish tail extending away from the Sun. The tail’s length can be impressive—often about twice the apparent diameter of the Moon—but visibility depends on sky darkness and atmospheric clarity.
Where to Look in the Sky
As of mid‑October, Comet Lemmon sits in the northwest before sunrise and in the northeast after sunset, drifting relative to the Big Dipper and its neighboring stars. The route through Ursa Major makes it relatively easy to locate with practice. Another nearby beacon is the bright star Cor Caroli in Canes Venatici; on Thursday, Oct. 16, Lemmon will pass within a degree of Cor Caroli, still keeping close to the Big Dipper’s vicinity.
For star‑hoppers who want a precise target, use finder charts from trusted sources or astronomy apps (In-The-Sky.com, Sky Guide, Stellarium, or SkySafari). These tools translate sky coordinates into a practical, real‑time map for your location.
Comet SWAN: A Fainter Companion in the Sky
Alongside Lemmon, a second comet, SWAN (C/2025 R2), will be visible in the same twilight window but much dimmer, at around magnitude 5.9. It resides in Ophiuchus and sits near Antares in Scorpius. While trickier to spot, binocular observers may still find it in the same 30‑minute session after sunset, but in the southwestern sky rather than near the Big Dipper.
Best Viewing Strategy
The short‑term forecast for Comet Lemmon is favorable around Oct. 20–21, which coincides with the Orionid meteor shower’s peak and a new moon. A new moon means darker skies—perfect for faint astronomical objects. Patience is essential; clouds and atmospheric conditions can quickly block a faint comet. Plan a few short viewing sessions across two to three evenings to maximize your chances.
What You Need to Watch
- Dark, open sky away from city lights
- Binoculars with steady support (and a comfortable stance or tripod)
- Clear forecast and patience for a quiet, dark observing session
- Up‑to‑date star charts or astronomy apps for your location
A Note on Observing Etiquette
Be mindful of light sources, avoid bright phones, and give your eyes time to adapt to the dark. A small red flashlight can help you preserve night vision while consulting charts.
Bottom Line
Comet Lemmon offers a rare chance to glimpse a long‑period visitor during its close approach to Earth. While not guaranteed to dazzle naked‑eye observers, binoculars are a wise companion for a satisfying view near the Big Dipper this week. If you miss Lemmon, watch for its 30‑minute windows in late October as it edges toward its closest distance, just as the Orionids light up the sky.
