Spotlight on Three Comets: Lemmon, SWAN, and ATLAS — What to Watch in 2025

Astronomy buffs, prepare for one of the most exciting comet seasons in recent years. Three comets — C/2025 A6 (Lemmon), C/2025 R2 (SWAN), and C/2025 K1 (ATLAS) — are making headlines for their predicted brightness, orbits, and viewing potential. This post brings you the latest on each, plus tips on when and how to see them.

Discovery & Orbit

• Discovered on January 3, 2025 by the Mount Lemmon Survey as an apparently asteroidal object. Wikipedia+2British Astronomical Association+2
• Precovery images from November 2024 confirmed its cometary nature. British Astronomical Association+3Wikipedia+3Aerith+3
• Orbital parameters: perihelion (closest to Sun) at 0.5299 AU, high eccentricity (~0.9957), and a long orbital period (~1,350 years inbound, ~1,155 years outbound). British Astronomical Association+3Wikipedia+3COBS+3

Brightness & Visibility

• The comet has already brightened more than originally expected. Some models now predict a peak brightness of magnitude ~4, possibly making it visible to the naked eye in dark skies. Unistellar Science+3Star Walk+3Space+3
• It will make its closest approach to Earth on October 21, 2025, at about 0.596 AU (≈ 89 million km) TheSkyLive+2Space+2
• It reaches perihelion on November 8, 2025. Unistellar Science+4Wikipedia+4Aerith+4
• In late September, it is located in the constellation of Lynx, rising early and visible before dawn in many northern locations. Astro Van Buitenen+3TheSkyLive+3Star Walk+3
• Some charts suggest by late October it could be circumpolar at latitudes above ~48° N (meaning it never sets below the horizon). Star Walk+2Space+2

Observing Tips

• For best view, use binoculars or a mid-sized telescope early in the morning when the sky is darkest and the comet is highest.
• Use star charts or apps (e.g. Stellarium) to track its path through constellations: Lynx → Leo Minor → Ursa Major → Canes Venatici etc. Star Walk+2Space+2
• Since comets are unpredictable, monitoring images and magnitude reports from observer networks (e.g., COBS, AERITH) is helpful. Unistellar Science+4COBS+4Aerith+4

2. Comet C/2025 R2 (SWAN)

Discovery & Characteristics

• Discovered on September 11, 2025, via the SWAN instrument aboard the SOHO spacecraft by Vladimir Bezugly. Wikipedia+2Space+2
• Its orbit is highly elongated (long-period comet), and initial observations place it at magnitude ~6.0. Wikipedia+2TheSkyLive+2

Brightness & Visibility

• The comet is becoming more visible, with reports noting a greenish coma and tail captured in recent telescopic images (September 17). EarthSky+1
• Some forecasts suggest it may brighten sufficiently to become visible to binoculars or even the naked eye by October (if predictions hold). Space+1
• It will pass relatively close to Earth, with its closest approach projected near 0.2606 AU (~38.99 million km) on October 20. TheSkyLive

Observing Tips

• Because it lies closer to the Sun’s direction in the sky, visibility will be tricky against twilight glare — early evening or pre-dawn windows may help.
• Use telescopes or long-exposure photography to reveal the green coma and faint tail.
• Sky mapping tools (e.g. TheSkyLive) provide updated ephemerides (right ascension, declination, rise/set times) to help track its path. TheSkyLive

3. Comet C/2025 K1 (ATLAS)

Discovery & Behavior

• C/2025 K1 (ATLAS) is currently less documented in mainstream sources, but it is part of the comet lineup for late 2025. SETI Institute
• It passed perihelion on October 8, 2025 (closest to Sun). SETI Institute
• Observers note a lack of a clear ion tail, possibly due to depletion in volatile materials like carbon. Facebook

Observing Potential

• Post-perihelion, the comet’s survival is not guaranteed — comets often disintegrate during close solar passes. SETI Institute
• Its closest approach to Earth is projected for November 26, 2025, making November a critical observation period. SETI Institute

What Makes This Season Special

• According to LiveScience, two comets (Lemmon and SWAN) may become visible in the same night, coinciding with the peak of the Orionid meteor shower (October 20–21). Live Science
• October 21 also features a new moon, reducing moonlight and improving dark-sky conditions for observing faint comets. Live Science+1
• This could mark a rare occasion where bright comets and meteor activity line up, offering observers a spectacular celestial show. Live Science

==> How to Track These Comets Using Stellarium & Apps

https://theskylive.com/planetarium?obj=c2025a6#ra|9.292640143717332|dec|38.650243619643014|fov|80

• Add by designation: In Stellarium, use “Comet” mode and enter the comet’s name or designation (e.g., “C/2025 A6”).
• Update ephemeris: In extended settings, use an orbital file (e.g. from NASA/JPL or Minor Planet Center) so Stellarium knows its path precisely.
• Switch to “All Models” view: This lets you see faint objects — adjust magnitude limits.
• Set observing location & time: Match your local coordinates and date/time to see where and when the comet will rise/set.
• Use zoom and field-of-view (FoV) presets: You can compare the comet’s location against known star fields to help find it in real sky observations.

Quick Summary Table

Final Notes & Advice

• These comets’ brightness predictions are not guarantees — comets are notoriously unpredictable.
• Use dark skies, binoculars, or telescopes.
• Combine your comet viewing with meteor showers (especially in mid-October) for a richer sky experience.
• Stay updated with comet tracking services (COBS, TheSkyLive, AERITH) for magnitude updates and orbital refinements.