This week offers a rare opportunity for stargazers as Comet C/2025 A6 (Lemmon) and Comet C/2025 R2 (SWAN) move in close proximity to Earth. Comet Lemmon is expected to reach its closest approach on Tuesday, October 21, while Comet SWAN will come even closer one day earlier, on October 20.
After a year of seeing few bright comets, this celestial event is exciting for astronomy enthusiasts. Comet Lemmon, with a brightness of magnitude 4.5, can potentially be spotted with the naked eye in dark skies. This brightness is comparable to that of the Beehive Cluster (M44) and slightly less than the Andromeda Galaxy (M31).
However, Comet SWAN is much fainter at magnitude 5.9, which means it will require binoculars to be seen. For those aiming to catch a glimpse of both comets, the best viewing time will be approximately an hour and a half after sunset each evening this week, with Comet Lemmon visible in the northwest sky and Comet SWAN located within the Summer Triangle constellation, which includes the stars Vega, Deneb, and Altair.
To find Comet Lemmon, locate the Big Dipper and follow its handle towards the bright star Arcturus, with the comet positioned about two-thirds of the way along that arc. It will be even higher in the sky on Tuesday night. For Comet SWAN, look for it situated halfway between Altair and the horizon in the southwestern sky.
For those interested in photography, numerous resources including finder charts and apps such as Sky Guide and SkySafari 7 Pro can assist in the process.
It’s noteworthy that while both comets are currently visible, they are on significantly different journeys. Comet Lemmon will come within 56 million miles (89 million kilometers) of Earth before looping around the sun on November 8. Its orbit, originally set for approximately 1,350 years, has been altered due to gravitational influences from Jupiter, which shortened its return cycle by nearly 200 years, delaying its next appearance until the year 3179.
As these comets grace our night sky, they serve as a reminder of the vast and dynamic universe we inhabit, inspiring a sense of wonder and curiosity about the cosmos.