Twin comet watch! Comets Lemmon and SWAN reach peak proximity and luminosity this week. Find out how to see them.

Comet C/2025 A6 (Lemmon) will make its closest approach to our planet this week, only a day removed from the unrelated celestial object C/2025 R2 (SWAN). (Image credit: Getty Images / Javier Zayas Photography)

If you are hoping to view a duo of comets, the start of this week offers the finest opportunity. Following a year devoid of comets luminous enough for observation without specialized tools, two — Comet C/2025 A6 (Lemmon) and Comet C/2025 R2 (SWAN) — have appeared simultaneously.

Comet Lemmon may bear a resemblance to a green citrus fruit, despite its moniker, yet on Tuesday (Oct. 21), this dusty cosmic snowball originating from the distant solar system will get as close to our globe as possible and likely radiate at its peak intensity. It has presently attained magnitude 4.5, as per SpaceWeather.com — roughly the same brightness exhibited by the Beehive Cluster (M44) during spring and only marginally fainter than the Andromeda galaxy (M31).

Although Comet Lemmon is, in theory, visible to the unaided eye under exceptionally dark skies, binoculars will be necessary to spot another, dimmer icy celestial wanderer, Comet C/2025 R2 (SWAN). Incredibly, Comet SWAN will approach Earth most closely on Monday (Oct. 20), preceding Comet Lemmon by a day, but its luminosity will be about three times less, measuring at magnitude 5.9. (In astronomical terms, a greater magnitude signifies a less luminous object.)

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The prime viewing window for both comets on any given evening this week will fall roughly an hour and a half subsequent to sunset; precise local times can be verified on Timeanddate.com. On Monday, Comet Lemmon will be discernible in the northwestern sky, proximal to the Big Dipper and the brilliant star Arcturus, and situated close to the horizon.

Trace the configuration of stars constituting the handle of the Big Dipper to “arc towards Arcturus”; the comet will lie approximately two-thirds along this path. By Tuesday, it will be marginally elevated in the sky. For Comet SWAN, direct your gaze towards the Summer Triangle, a stellar assembly comprised of Vega, Deneb, and Altair — in the southwestern expanse. You’ll locate Comet SWAN approximately midway between Altair and the skyline.

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Valuable finder charts and celestial maps tailored for both comets are accessible at The Sky Live, In-The-Sky.org and Stellarium, along with mobile apps such as Sky Guide, Sky Tonight, and SkySafari 7 Pro. Should you desire to capture the comets photographically, our manual offers comprehensive guidance.

The two comets traverse vastly dissimilar trajectories. Comet Lemmon will draw within 56 million miles (89 million kilometers) of Earth on Tuesday, as indicated by The Sky Live, en route to circling the sun on Nov. 8 during its 1,350-year solar orbit. (Nonetheless, Jupiter diminished some of Comet Lemmon’s orbital impetus, curtailing its period by almost 200 years, as per Star Walk, thus its return will be delayed until 3179.)

Comet SWAN constitutes a long-period comet, completing an orbit of the sun every 20,000 years, according to Universe Today, and on Monday, it will reside 24 million miles (39 million km) distant as it departs the inner regions of the solar system. This equates to roughly a quarter of the expanse separating Earth and the sun.

Jamie CarterSocial Links NavigationLive Science contributor

Jamie Carter functions as a freelance reporter and a consistent Live Science contributor, with his base in Cardiff, U.K. He is the author of A Stargazing Program For Beginners and delivers lectures pertaining to astronomy and the natural realm. Jamie regularly contributes to Space.com, TechRadar.com, Forbes Science, BBC Wildlife magazine and Scientific American, among numerous other venues. He also curates WhenIsTheNextEclipse.com.

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