Two Green Comets Visible in Northern Hemisphere Skies
Comets Lemmon and SWAN, originating from the Oort Cloud, are currently observable in the Northern Hemisphere, offering a rare celestial display.
Two bright green comets, Lemmon and SWAN, are currently visible to observers in the Northern Hemisphere. Both comets originate from the distant Oort Cloud, a region beyond Pluto. Comet Lemmon is expected to make its closest approach to Earth around October 21, while Comet SWAN will have its nearest flyby on October 20.
Carson Fuls, director of the Catalina Sky Survey at the University of Arizona, noted that spotting two comets simultaneously without special equipment is "rare, but not unprecedented." To view these comets, skywatchers should go outside just after sunset. Comet Lemmon can be found low in the northwestern sky, while Comet SWAN will appear in the southwestern sky, positioned just below the bright star Sabik in the constellation Ophiuchus.
Both comets are green due to gases streaming off their surfaces. From Earth, they may appear as gray, fuzzy patches. Comets are frozen remnants from the solar system's formation billions of years ago. As they approach the sun, they heat up, releasing characteristic streaming tails.
Comet Lemmon, also designated C/2025 A6, was discovered in January by a telescope scanning the night sky for near-Earth asteroids. Comet SWAN, known as C/2025 R2, was spotted in September by an amateur astronomer using images from a spacecraft operated by NASA and the European Space Agency.
Earlier this year, a green comet broke up as it passed by the sun, disappointing those hoping for a naked-eye spectacle. Notable comet flybys in recent years include Tsuchinshan-Atlas in 2024, Neowise in 2020, and Hale-Bopp and Hyakutake in the 1990s.