This month is shaping up to be a prime time for comet enthusiasts. A fascinating array of these celestial bodies, trailed by shimmering wisps of gas and dust, are currently traversing our cosmic neighborhood. For skywatchers in the Northern Hemisphere, October offers a unique opportunity to observe not just one, but two once-in-a-lifetime comets lighting up the autumn skies.
These remarkable visitors, scientifically designated as C/2025 A6 (Lemmon) and C/2025 R2 (SWAN), have journeyed from the remote edges of our solar system, where the sun appears as nothing more than a faint pinprick in the vast darkness.
Comet A6 (Lemmon) was initially identified in January by the Mount Lemmon Survey, an initiative that meticulously catalogues near-Earth objects from its observatory atop an Arizona mountain.
Comet R2 (SWAN), on the other hand, made a more unexpected entrance in early September. It was discovered by Vladimir Bezugly, a Ukrainian amateur astronomer, who found its signature in publicly accessible images from SWAN – the Solar Wind Anisotropies instrument aboard the Solar and Heliospheric Observatory spacecraft, positioned nearly a million miles from Earth.
“The comet caught everybody by surprise,” noted Quanzhi Ye, an astronomer at the University of Maryland. This unexpected arrival was due to the comet’s trajectory, which brought it from the direction of the sun, keeping it obscured by our star’s glare and hidden from ground-based telescopes during its approach.
What is a comet?
Comets are ancient remnants of the solar system’s formation, essentially chunks of ice and rock that have survived for billions of years. As a comet approaches the sun, it begins to warm up. This causes some of its ice to sublimate directly into gas, which then streams away into space, carrying dust particles with it and forming the distinctive, luminous tail.
When will R2 (SWAN) be visible?
After captivating stargazers in the Southern Hemisphere, Comet R2 (SWAN) is now beginning its display in the Northern Hemisphere’s evening sky. It will remain visible throughout October.
To maximize your chances of spotting it, astronomers advise finding a dark location with an unobstructed view to the southwest and minimal light pollution. R2 (SWAN) is not expected to be visible to the naked eye, so binoculars or a small telescope will be essential. Approximately 45 minutes to an hour after sunset, begin scanning low along the horizon. Yoonyoung Kim, a comet researcher at the University of California, Los Angeles, describes its appearance as a “fuzzy ball.”
For those with smartphones, Mr. Ye suggests a helpful trick: set your camera’s exposure to a few seconds and capture some images of the sky. This can sometimes reveal fainter objects.
Astronomers anticipate that observing conditions for R2 (SWAN) will steadily improve as it makes its closest approach to Earth on October 20. Each night, the comet will ascend higher into the sky, moving further from the lingering twilight glow.
Comets, however, are notoriously unpredictable, often likened to cats due to their capricious nature. They have tails, and they often do as they please. This means R2 (SWAN) could still surprise us; it brightened significantly upon its initial discovery and might undergo another outburst, potentially becoming visible without binoculars, according to Mr. Ye.
Conversely, there’s also the possibility that the comet could entirely disintegrate.
“We are all wondering what it’s going to do next,” he added.
How do I see A6 (Lemmon)?
Comet A6 (Lemmon) is currently visible in the northern morning sky. To observe this comet, you’ll also need binoculars or a small telescope, along with the determination to wake up before dawn.
Look for a fuzzy object in the northeast, several hours before sunrise, positioned just below the familiar ladle shape of the Big Dipper. From our vantage point on Earth, A6 (Lemmon) will transition halfway through the month, appearing in the evening sky to the west. If current predictions hold true, A6 (Lemmon) is expected to brighten further in late October and early November, possibly enough to be glimpsed with the naked eye under extremely dark conditions.
Will it be possible to see both comets at once?
Stargazers might actually have the chance to spot both comets around Halloween, according to David Dickinson, an amateur astronomer and author of “The Backyard Astronomer’s Field Guide.”
However, A6 (Lemmon) will remain very low on the horizon and could be obscured by twilight, as Mr. Dickinson noted. R2 (SWAN) will be higher in the sky for several hours after sunset, making it potentially your best bet for an evening spectacle.
Where did these comets come from?
Distant comets like A6 (Lemmon) and R2 (SWAN) originate from the Oort cloud, a vast, spherical region of icy objects that envelops the solar system at its furthest reaches. Carrie Holt, an astronomer at Las Cumbres Observatory in California, suggests that such comets were likely “perturbed inward to the inner solar system a very, very, very long time ago,” perhaps nudged by a passing star or the gravitational tides of the Milky Way.
According to astronomers’ latest calculations, A6 (Lemmon) completes an orbit around the sun approximately every 1,359 years, while R2 (SWAN) finishes its loop in 619 years.
Other comets reside closer in, within the Kuiper belt beyond Neptune, typically completing an orbit in less than 200 years. There are also interstellar comets that visit our solar system, such as 3I/ATLAS, which is currently passing through the inner solar system but will be on the far side of the sun for viewing this month.
For comet researchers, these visits from the Oort cloud are invaluable lessons in cosmic history. Due to their prolonged isolation from the sun’s warmth, these comets retain materials as pristine as they were over four billion years ago, offering scientists a direct glimpse into the very beginnings of our celestial home.
Should they survive their journey past the sun without disintegrating, both comets will eventually return to the frigid outer reaches of the solar system, forever altered by their brief, exhilarating sojourn.
Out there, as Mr. Ye describes it, “it’s actually pretty boring because it’s cold, and there’s not much going on.” This close flyby of Earth might just be the most exciting event these comets have experienced in decades, unfolding right above our heads. So, as Mr. Ye aptly puts it, “why not just go see?”