Skywatchers could be treated to a rare double feature this October as two comets — C/2025 R2 (SWAN) and C/2025 A6 (Lemmon) — are forecast to brighten around the same time. Both are expected to make their closest approach to Earth around Oct. 21, possibly even reaching naked-eye visibility under dark skies. That coincides with the peak of the Orionid meteor shower and the new moon, setting the stage for potentially one of the most impactful celestial displays in years.
Comets SWAN and Lemmon look set to offer a rare chance to see a pair of bright visitors within days of each other, and possibly on the same evening for observers in the Northern Hemisphere.
About 45 minutes after sunset on Tuesday, Oct. 21, is when to circle in your diary, with SWAN and Lemmon low in the post-sunset western and northern skies, respectively.
SWAN will be visible beneath the Summer Triangle stars while Lemmon will move more quickly across the sky beneath the Big Dipper.
Although both could become bright enough to be seen in dark skies (such as a Dark Sky Place or somewhere with dark western and northern horizons on a light pollution map), binoculars may be required. The brightness of comets is famously hard to predict. Both could undergo an outburst and either brighten or fade.
Both comets will begin to be visible once the moon is down in the post-sunset hours around Oct. 9, though Oct. 21 is when to plan a trip to dark skies, not least because that's also the night the Orionid meteor shower peaks.
Only discovered in September, Blueish-green Comet SWAN (C/2025 R2) is destined to become visible to observers at mid-northern latitudes starting the second week of October, according to Sky & Telescope, visible low in the southwestern sky in the constellation Libra at dusk.
SWAN will brighten and move higher into the sky during October as it moves northeastward into Scorpius and into Ophiuchus, then Serpens. On Oct. 13, SWAN will pass just beneath Sabik, a bright star in Ophiuchus. It's expected to be at its best around Oct. 21, when it gets closest to the sun. It will then recede from Earth, dimming as it does.
Discovered in January by the Mount Lemmon Survey in Arizona, comet Lemmon has been steadily brightening as it approaches Earth, which it will also do on Oct. 21. Comet SWAN begins in October, rather close to the sun as seen from the Northern Hemisphere, so it's not far above the horizon at dusk. Around Oct. 12, Lemmon will become visible low in the northwest, close to the Big Dipper. On Oct. 16, it will pass within a degree of the bright star Cor Caroli in the constellation Canes Venatici.
Adding to the spectacle, the Orionid meteor shower peaks on October 21-22, producing about 20 meteors per hour under clear, dark skies. They'll be best seen after midnight through dawn, when the constellation Orion rises high in the southeast. The Orionids are caused by debris from Halley’s Comet, and their streaks of light will appear to radiate from Orion. The timing is nearly perfect because the peak coincides with the new moon on Oct. 21, ensuring completely dark conditions for both comets and “shooting stars.”