Two Comets Will Streak Across the Sky in October. Here’s When to Look.

The skies of 2025 have been busy. Right now, three comets are sailing through the inner solar system. You might have read some of my articles about 3I/ATLAS, which might be just a regular old comet that acts a little more strangely than most, or could be aliens. Depends on which astrophysicist you’re listening to.

There are a couple of new ones out there to keep your eyes on: Comet Lemmon (C/2025 A6) and Comet SWAN (C/2025 R2). Both are lighting up the Northern Hemisphere skies with a green haze this month, assuming the skies where you live aren’t being polluted with city lights.

First spotted by Arizona’s Mount Lemmon Survey in January, Comet Lemmon is the main event. On or around October 21, the same night as a new moon, Lemmon is expected to hit peak brightness, making it visible to the naked eye. No binoculars or telescope necessary. Just look out for the emerald glow in the sky, which, if you’re curious, is made up of carbon molecules in the comet’s coma that are fluorescing under solar radiation.

As of mid-October, Lemmon has been hanging out near Ursa Major in the pre-dawn sky, soon transitioning to evening visibility as it heads west. If you’re at all interested, you really should try to see it, since it won’t be around again until 3175.

Comet SWAN, meanwhile, is its less flashy celestial buddy. It was only discovered last month by an amateur poring over NASA satellite data. Swan is best seen about 90 minutes after sunset, as it’s hanging low in the southwestern sky. It will be closest to Earth (and therefore most visible) on October 19. You’ll probably need binoculars or a small telescope for this one, but it’s doing all it can to be seen by us here on Earth as it slowly brightens as it approaches the planet.

And then, of course, there’s the aforementioned comet/alien artifact 3I/ATLAS. It’s not of our solar system, and no one is quite sure what it even is yet, though one thing astrophysicists from all over the world can agree on is that it certainly is weird, and it does weird things that comets don’t normally do. It’s currently being observed from Mars by NASA’s Perseverance rover.