On the evening of October 21, 2025, skywatchers are in for a rare celestial treat: not one but two comets—C/2025 R2 (SWAN) and C/2025 A6 (Lemmon)—will be bright enough to spot with the naked eye. To make the night even more special, it also falls on the new moon, meaning the sky will be as dark as it gets, free of interfering moonlight. That gives observers the best possible conditions to enjoy both comets on the same night—a truly extraordinary opportunity for amateur and seasoned astronomers alike.

What is a Comet?

Comets are often described as “dirty snowballs” — icy leftovers from the formation of our solar system. Most originate in two distant reservoirs: the Kuiper Belt, a ring of icy bodies beyond Neptune, and the Oort Cloud, a vast spherical shell much farther away. When a comet ventures close to the Sun, heat causes its ices to sublimate, releasing gas and dust that form its characteristic coma (the glowing cloud around the nucleus) and tail (which always points away from the Sun due to the solar wind). Comets are unpredictable by nature; some brighten spectacularly into “Great Comets,” while others fizzle or even disintegrate.

Meet the Two October Visitors

C/2025 R2 (SWAN)

The first of the two comets, C/2025 R2 (SWAN), was discovered in September 2025 by the SWAN instrument aboard the SOHO spacecraft. Although the camera’s primary job is to study hydrogen around the Sun, it has become famous for spotting comets as well. SWAN is believed to be a long-period visitor from the distant Oort Cloud, a frozen reservoir of icy bodies at the edge of our solar system. On October 19, the comet will pass within about 0.26 astronomical units of Earth—roughly 39 million kilometers. If predictions hold, it may brighten to between magnitude +4 and +5, which puts it just on the edge of naked-eye visibility under dark skies, though binoculars will make it much easier to see.

C/2025 A6 (Lemmon)

The second comet, C/2025 A6 (Lemmon), has been on astronomers’ radar since its discovery in January 2025 by the Mount Lemmon Survey in Arizona. Like SWAN, it likely hails from the Oort Cloud, traveling on a long and elongated orbit that has brought it into the inner solar system. Lemmon will reach its closest approach on October 20–21, when it passes about 0.60 astronomical units from Earth, or nearly 89 million kilometers away. At that point, it is expected to shine at magnitude +4 to +6, giving observers a chance to glimpse it with the naked eye under pristine skies, but more reliably with binoculars or a telescope.

An Even Rarer Coincidence

The chance to see two comets in the sky at the same time is unusual. Adding to the spectacle, their closest approaches happen within just two days of each other — and right as the Orionid meteor shower is peaking. For backyard astronomers, October 21 offers a “triple play” of comets, meteors, and crisp autumn skies.

Where and How to Observe

As the comets approach their closest alignment with Earth around October 21, here’s roughly where to look, and which stars and constellations to use as landmarks:

Comet C/2025 R2 (SWAN)

Look for Comet C/2025 in the southwestern skies in southeastern Aquila at RA/DEC: 19h 37m47.5s -10°46’54.6″ from sunset until around midnight when it sets.

Comet C/2025 A6 (Lemmon)

The window for Comet C/2025 A6 (Lemon) is much shorter. Catch it roughly 10° above the bright star Arcturus in the northwestern sky in central Boötes at RA/DEC: 14h 36m12.9s +27°42’50.3″ from sunset until roughly 9:00 PM when it sets.

Observing Tips

• Get a clear, open view in southeastern Aquila (for SWAN) and northwest toward central Boötes (for Lemmon) on October 21st

• If you want to see both comets at roughly their brightest on the same evening, start looking just after sunset on October 21st.

• Use the charts and coordinates above to help find the comets. Planetarium software is also helpful.

• If you’re observing on an evening other than October 21st, you’ll find that the comets move noticeably from night to night. It’s best to consult a star chart or an app (e.g. Stellarium, SkySafari, or your app of choice) loaded with their predicted ephemerides.

• Let your eyes adapt fully to the dark, and scan slowly with binoculars, starting from the reference stars and moving outward in a “star hop” fashion.

Keep Looking Up

Whether they blaze brightly or remain faint smudges, October’s twin comets remind us of the dynamic and unpredictable nature of the cosmos. Don’t miss the chance to step outside on October 21 and try to catch a glimpse of these icy visitors that have traveled millions of years from the edges of our solar system just to swing by our skies.

Clear skies and happy comet-hunting!