Stargazers across the Northern Hemisphere are in for a rare celestial treat this October, as not one but two bright green comets grace the evening skies. The cosmic duo—Comet Lemmon (C/2025 A6) and Comet SWAN (C/2025 R2)—have captured the imagination of amateur astronomers and seasoned skywatchers alike, with their vibrant color and simultaneous visibility making headlines around the world.
According to the Associated Press, both comets hail from the farthest reaches of our solar system, possibly originating in the mysterious Oort Cloud, a vast shell of icy bodies that lies far beyond the orbit of Pluto. This distant birthplace means that these comets have spent billions of years in deep freeze, only now making their way into the inner solar system for a fleeting visit.
Comet Lemmon, first spotted in January 2025 by a dedicated telescope scouring the night sky for near-Earth asteroids, is expected to make its closest approach to Earth on or around Tuesday, October 21, 2025. Meanwhile, Comet SWAN, discovered more recently in September by an amateur astronomer poring over images from a NASA and European Space Agency (ESA) spacecraft, will have its closest flyby with Earth on Monday, October 20, 2025. However, as Comet SWAN is already heading away from the sun, experts anticipate it will begin to dim in the days following its closest approach.
Spotting two comets at once—especially without the aid of telescopes or specialized equipment—is an event that doesn’t come around often. "Rare, but not unprecedented," is how Carson Fuls, director of the University of Arizona-based sky survey responsible for discovering Comet Lemmon, described the phenomenon to the Associated Press. For those eager to catch a glimpse, the best chance comes just after sunset: Comet Lemmon will appear low on the northern horizon, while Comet SWAN can be found near the southwestern horizon. Both are likely to remain visible with binoculars through the end of October, though their brightness may wane as the month progresses.
Valerie Rapson, an astronomer at the State University of New York at Oneonta, cautioned that while the double comets are currently bright enough for binocular viewing, their ultimate visibility remains uncertain: "Experts aren’t yet sure how bright they’ll remain," she told reporters, highlighting the unpredictable nature of these icy wanderers.
What makes these comets particularly eye-catching is their striking green hue. This color is not just for show—it’s the result of gases streaming off their icy surfaces as they heat up on their journey toward the sun. Specifically, the green glow comes from diatomic carbon (C2) and cyanogen, which fluoresce under the sun’s ultraviolet light. But don’t expect to see a brilliant emerald streak with the naked eye; from Earth, the comets appear more like gray, fuzzy patches, their true colors only revealed in long-exposure photographs.
Comets have long fascinated humanity, both for their beauty and for the mysteries they carry from the earliest days of the solar system. These frozen leftovers are time capsules, preserving material from billions of years ago. As they approach the sun, their ices vaporize, creating the iconic glowing comas and streaming tails that have inspired awe—and sometimes fear—throughout history.
This isn’t the first time in recent memory that a green comet has captured public attention. Earlier in 2025, anticipation ran high for another green comet expected to dazzle viewers. Unfortunately, that comet broke apart as it swung by the sun, dashing hopes for a naked-eye spectacle. Such disappointments are not uncommon; comets are notoriously fickle, their brightness and integrity subject to the whims of solar heat and gravitational forces.
Still, the current double act of Lemmon and SWAN has revived excitement among astronomers and the public. The last few years have seen several notable cometary visitors: Tsuchinshan-Atlas made a memorable pass in 2024, while Neowise lit up the skies in 2020. Going further back, the spectacular appearances of Hale-Bopp and Hyakutake in the 1990s remain etched in the memories of those who witnessed them.
The discovery stories of Lemmon and SWAN also speak to the evolving nature of astronomy. Comet Lemmon was found by a professional survey designed to track potentially hazardous asteroids, a reminder of the dual purpose many sky-watching programs now serve. Comet SWAN, on the other hand, was spotted by an amateur astronomer—proof that, even in the age of giant telescopes and space probes, there’s still room for backyard enthusiasts to make meaningful contributions. The images that led to SWAN’s discovery came from a spacecraft jointly operated by NASA and ESA, underscoring the increasingly international and collaborative spirit of space science.
For those hoping to catch the show, timing and location are key. As the AP reports, the best views come just after sunset. Find a spot with a clear view of the horizon—city lights and tall buildings can make things tricky—and scan the northern horizon for Lemmon and the southwestern horizon for SWAN. Binoculars will vastly improve your chances, as the comets’ fuzzy patches may be too faint for the unaided eye, especially as they begin to dim in late October.
Of course, the thrill of comet-watching isn’t just about ticking off a box on a stargazer’s checklist. It’s a chance to connect with the cosmos, to witness firsthand the ancient leftovers that helped build our planet and everything on it. As astronomer Valerie Rapson put it, there’s something special about watching these icy time travelers make their brief appearance. "Comets are frozen leftovers from the solar system’s formation billions of years ago. They heat up as they swing toward the sun, releasing their characteristic streaming tails," she explained to the Associated Press.
While the current display may not rival the legendary comets of past decades, it’s a reminder that the universe still has surprises in store—and that sometimes, all you need to do to experience them is step outside and look up. The green glow of Lemmon and SWAN may be fleeting, but for those who catch a glimpse, the memory is sure to linger long after the comets themselves have vanished back into the darkness beyond Pluto.
