What Is Comet Lemmon?
Comet Lemmon, officially designated C/2025 A6 (Lemmon) and also known as Comet A6, is a large, long-period comet tracing a dramatic 1,350-year orbit around the sun. First discovered on January 3, 2025 by the Mount Lemmon Survey near Tucson, Arizona, the comet is now making a temporary and accessible appearance for observers in the Northern Hemisphere. Its bluish, elongated tail stretches roughly twice the apparent diameter of the Moon and points directly away from the Sun, giving it a distinct, diffuse glow when viewed through binoculars.
Why This Week Is Special
As Comet Lemmon moves closer to Earth, its brightness is increasing. By Tuesday, October 21, it will reach its closest approach at about 55.4 million miles (89.2 million kilometers). This favorable geometry coincides with the peak of the Orionid meteor shower, offering a rare opportunity to observe a comet and meteor activity in a single twilight window. While the comet’s magnitude has already reached around +5.2—barely within naked-eye visibility—conditions such as a truly dark sky are essential to spot it without optical aid. A pair of binoculars remains the easiest way to enjoy the view this week.
Where To Look: Location Relative To The Big Dipper
Comet Lemmon is skirting the northwest before sunrise and the northeast after sunset, making the constellation Ursa Major—the Great Bear and home to the Big Dipper—a reliable anchor. The Big Dipper is a circumpolar feature, visible most nights from northern latitudes, circling Polaris. For best results, locate the Big Dipper first, then follow a faint, fuzzy patch just beyond its outer edge as Lemmon drifts through the night sky.
Best Viewing Times
The prime observing window is roughly 30 minutes, starting about 90 minutes after sunset for evening viewing. If you’re an early riser, a similar 30-minute window begins about 90 minutes before sunrise. In late October, Lemmon will be in the constellation Ursa Major and close to the bright star Cor Caroli in Canes Venatici on October 16, a reminder that the area around the Big Dipper remains a productive target for binocular stargazers.
Visibility Details: Brightness, Distance, and Sky Conditions
From October 12 to October 18, Comet Lemmon will travel from roughly 66 million miles (106 million kilometers) down to about 56 million miles (91 million kilometers) from Earth. This proximity typically yields a brighter appearance, but magnitude estimates around +5.2 mean you’ll want a dark, clear sky to see Lemmon with the naked eye. Binoculars are highly recommended, as they provide a comfortable, detailed view of the comet’s diffuse coma and faint tail without the need for perfect dark-sky conditions.
What About Comet SWAN?
A companion target this week is Comet SWAN (C/2025 R2), located in Ophiuchus and presenting a magnitude near 5.9. It sits in the southwestern sky about 90 minutes after sunset, above Antares in Scorpius. Like Lemmon, SWAN is best pursued with binoculars and a steady, dark sky; both comets are a test of patience and good observing timing rather than guaranteed brightness.
Practical Tips for a Successful Night
- Check local weather and plan for a moonless night; October 20 brings a new moon, which helps visibility for faint objects.
- Find a dark-site with a clear line of sight to the northern horizon.
- Use a sky map or stargazing app to pinpoint Lemmon’s position relative to the Big Dipper and Canes Venatici.
- Give your eyes 15–20 minutes to adapt to darkness, and avoid bright lights nearby.
Why Bother? The Science and the Awe
Comet Lemmon represents a rare, long-period visit from the distant Oort Cloud, offering a chance to glimpse a solar-system traveler on a centuries-long journey. Observing such comets through binoculars connects skywatchers with the mechanics of our solar neighborhood, alongside the seasonal rhythms of the Orionid meteor shower. Even if the brightness isn’t spectacular, the experience of finding a distant visitor near the Big Dipper is a memorable event for both new stargazers and seasoned observers.
How To Find Reliable Guidance
If you’re unsure about the comet’s exact position on any given evening, use helpful resources like In-The-Sky.com finder charts or popular stargazing apps such as Sky Guide, Stellarium, and SkySafari. These tools translate complex celestial motion into simple, time-specific guidance that works well for binocular viewing of Lemmon near the Big Dipper.
