Comet C/2025 A6 (Lemmon) was discovered on January 3, 2025 by the Mount Lemmon Survey in Arizona. It’s a long-period comet that last visited the inner solar system over a thousand years ago. The comet will make its closest approach to Earth around October 21, 2025, passing about 89 million km (0.6 AU) away, and it will reach its closest point to the Sun (perihelion) on November 8, 2025. Because of its steep, retrograde orbit, it’s a rare visitor traveling in from the outer reaches of the solar system.
Throughout October and early November, Comet Lemmon is expected to brighten considerably, possibly reaching magnitude 4 to 2.5, which could make it visible to the naked eye from dark locations. It will appear best in the evening sky just after sunset, primarily for observers in the Northern Hemisphere. During this time, it moves through constellations like Ursa Major, Boötes, Serpens, and Ophiuchus, and a good pair of binoculars or a small telescope will reveal its faint greenish coma and developing tail.
The comet’s green glow comes from gases such as diatomic carbon reacting to sunlight, and astrophotographers are already capturing images showing its long dust and ion tails. While it won’t rival spectacular comets like Hale-Bopp or NEOWISE, C/2025 A6 (Lemmon) is still one of the most promising comets of 2025 and worth watching this fall—especially around late October when it’s closest and brightest.
These images of Comet Lemmon were taken with a simple DSLR setup using a 55-200mm lens on a sky tracker. Click on any of the images below to go to the gallery for a better view and for more information.
