Skywatchers are in for a treat as Comet C/2025 A6 (Lemmon) makes its journey through the solar system, anticipated to be one of the most luminous comets of autumn 2025. Discovered on January 3, 2025, by the Mount Lemmon Survey, the comet was initially perceived as an asteroid due to its faintness but has since steadily increased in brightness, with predictions suggesting it could be visible to the naked eye under clear, dark conditions.
The comet's journey began with its initial observation at the Mount Lemmon Observatory in Arizona, a facility known for its astronomical discoveries. Further analysis confirmed its cometary nature, marked by a developing coma and tail. Comet C/2025 A6 (Lemmon) follows an orbital path with a period of approximately 1,350 years, which will be slightly shortened after its close pass to the Sun.
Key dates for observers are approaching. The comet is expected to reach its closest point to Earth on October 21, 2025, at a distance of about 89.16 million kilometers (0.60 AU). It will then achieve perihelion, its closest approach to the Sun, on November 8, 2025, at approximately 79.25 million kilometers (0.53 AU). During its closest approach to Earth, the comet is anticipated to be visible in the evening sky, approximately 42 degrees from the Sun.
Brightness predictions for Comet C/2025 A6 (Lemmon) range from magnitude +4 to +5, which would make it visible to the unaided eye, to more conservative forecasts of magnitude +7.3, requiring binoculars or a small telescope. Recent observations indicate a significant brightening trend, with some experts suggesting it could be roughly 250 times brighter than initially predicted. For optimal viewing, observers are advised to seek locations away from light pollution.
In early October, the comet will be situated in the constellation Ursa Major. By mid-October, it will transition into the evening sky, becoming visible low in the northwest after sunset. The Northern Hemisphere is expected to have the most favorable viewing conditions, with the comet potentially becoming circumpolar for latitudes above 48° N by late October. As the comet fades after its perihelion, it will become visible in the Southern Hemisphere in mid-November. The period from late October to early November is anticipated to be the prime viewing window for this celestial event.