How to See Comet C/2025 R2 (SWAN) & Comet Lemmon in the October 2025 Sky
Introduction
October 2025 brings a rare celestial treat: two comets—Comet C/2025 R2 (SWAN) and Comet Lemmon (C/2025 A6)—may be visible in the night sky. Skywatchers across the world are already preparing binoculars, telescopes, and dark-sky plans.
From Space.com: Comet SWAN can be found in the evening sky throughout October. Space
From WIRED: Comet Lemmon will reach its closest approach to Earth around October 21, making it brighter and potentially visible to the naked eye. WIRED
Let’s dive into details—when and where to look, how bright they might get, and how to photograph them.
Comet C/2025 R2 (SWAN) — What to Expect
Discovery & Orbit
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Comet SWAN was discovered using images from the Solar Wind Anisotropies (SWAN) instrument aboard the SOHO spacecraft. Star Walk+3Live Science+3Planetary Society+3
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The comet reached perihelion (its closest point to the Sun) on September 12, 2025. Space+3Star Walk+3EarthSky+3
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Its closest approach to Earth is expected on October 20, 2025, at about 0.26065 AU (≈ 38.99 million kilometers). TheSkyLive
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Its orbital period is very long—if visible, it might be a once-in-many-years event. EarthSky+2Star Walk+2
Brightness & Visibility
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Some forecasts suggest SWAN might brighten close to naked-eye levels under dark skies. Planetary Society+4Gadgets 360+4Live Science+4
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However, many projections expect it to remain easier to see with binoculars or small telescopes. Live Science+2Planetary Society+2
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On October 16, the comet is expected to lie about 5° upper-left of the star Xi Serpentis in the eastern part of Serpens. Space
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Later in the month, SWAN will travel through southern constellations and eventually sit above the southern horizon, between Sadalmelik and Sadalsuud in Aquarius. Space
When & Where to Look
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Best time: just after sunset, before the comet drops low on the southern/southwestern horizon. Space+2Planetary Society+2
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Use a sky app or planetarium software to help locate reference stars like Xi Serpentis or constellation lines. Space+1
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Observers at mid-northern latitudes are favored for much of its apparition. Planetary Society+2EarthSky+2
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A darker sky (far from city light) improves your chance to see even a faint comet.
Tips & Photography
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A pair of 10×50 binoculars is a great starting tool.
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If possible, use a tracking equatorial mount and long exposures to bring out the tail and detail.
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Try stacking images to improve signal-to-noise ratio.
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Use reference stars in the same field to help locate the comet in your frames.
Comet Lemmon (C/2025 A6) — Brightening Fast
Discovery & Orbit
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Comet Lemmon was discovered in January 2025 by the Mount Lemmon Survey in Arizona. NASA Space News+3WIRED+3Space+3
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Its closest approach to Earth (perigee) occurs around October 21, 2025, at ~0.59617 AU (~89.2 million km). EarthSky+3TheSkyLive+3Space+3
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Its perihelion (closest to the Sun) is expected on November 8, 2025. WIRED+2Space+2
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Estimates suggest it may brighten to magnitude +4 to +5—possibly visible to the naked eye under dark skies. Star Walk+4Space+4Space+4
Expected Brightness & Visibility
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If brightness predictions hold, Lemmon may start to be seen with the naked eye, with better visibility through binoculars or telescopes. Astronomy+3Space+3Space+3
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In early October, Lemmon is a morning object in the eastern sky. Astronomy+2NASA Space News+2
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By mid-October, it transitions into the evening sky, visible after sunset in the northwest direction. Space+2NASA Space News+2
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Around October 17, in some latitude settings, Lemmon might appear ~12° above the horizon ~90 minutes after sunset. Astronomy
When & Where to Look
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Early October: look before dawn in the east.
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Mid-to-late October: shift your viewing time to after sunset, toward the northwest horizon. Space+2Astronomy+2
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Avoid bright moonlight and light pollution for best results.
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Use sky charts or apps to track its movement among constellation stars.
Tips & Photography
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Because comet brightness changes rapidly, check updated ephemeris charts frequently.
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Use long exposures, star stacking, and dark sky sites to bring out any subtle tail features.
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If the comet approaches magnitude ~4 or 5, it may show a faint greenish glow from diatomic carbon emissions (C₂) in its coma. Space+2Space+2
Two Comets & A Meteor Shower — An October Spectacle
It’s not just one, but two comets visible simultaneously in October 2025:
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Comet SWAN in the evening sky
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Comet Lemmon transitioning from morning to evening visibility
This rare conjunction may coincide with the Orionid meteor shower, which peaks on October 20–21. The Washington Post+1
That means under clear, dark skies, you might catch comets and meteors in the same stargazing session.
You’ll want to:
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Plan for a moon-free night (new moon window) for best contrast.
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Stay out late or start early based on which comet you're targeting.
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Bring binoculars, a telescope if available, and a star map / app.
Quick Comparison Table
| Feature | Comet SWAN (C/2025 R2) | Comet Lemmon (C/2025 A6) |
|---|---|---|
| Closest Earth Approach | ~October 20, 2025, ~0.26065 AU (~39 million km) TheSkyLive | ~October 21, 2025, ~0.59617 AU (~89 million km) TheSkyLive+1 |
| Brightness Forecast | Possibly near naked-eye, but more reliably seen with binoculars/telescope Planetary Society+3Live Science+3Gadgets 360+3 | Forecast to reach magnitude ~4–5 Space+3Space+3Space+3 |
| Best Viewing Time | After sunset, before it dips below horizon Space+1 | Early October – morning sky; mid/late October – evening sky Astronomy+2NASA Space News+2 |
| Key Constellations / Reference | Serpens, Aquarius, near Xi Serpentis Space | Moves through eastern sky then into northwest after sunset Space+1 |
Pro Tips for Amateur Astronomers
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Check updated ephemerides nightly — both comets move, and brightness predictions can change.
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Pick a dark observing site — city lights will drown out faint comets.
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Use a red flashlight or red filter — to preserve night vision.
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Start with binoculars — 10× or 12× can reveal comets too faint for the naked eye.
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Stack and align images against background stars to bring out faint tails.
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Watch the horizon line — comets often stay low; plan for an unobstructed view.
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Be flexible — if a comet doesn’t appear one night, conditions or brightness may improve the next.
Conclusion
October 2025 presents a rare double treat: Comet SWAN and Comet Lemmon may both grace our skies. With luck, they could even be seen by the naked eye under dark conditions. Add in the Orionids meteor shower for extra excitement, and this month might deliver one of the most beautiful sky shows of the year.
Don’t wait—this is your chance. Mark your calendar, find a dark site, and keep your eyes on the skies.
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