A newly discovered comet, designated as Comet C/2025 R2 (SWAN), is set to become a highlight in the evening sky this October. On September 10, Ukrainian astronomer Vladimir Bezugly identified the comet while analyzing images from the Solar Wind Anisotropies (SWAN) camera aboard the Solar and Heliospheric Observer (SOHO) spacecraft. The comet, described as exceptionally bright by Bezugly, marks the 20th official SWAN comet discovery.
Since its initial sighting, amateur astronomers, especially in the Southern Hemisphere, have reported observing the comet. On September 15, the comet received its formal designation from the International Astronomical Union (IAU).
Astronomers measure a comet’s brightness using a scale known as magnitude. Lower numbers indicate brighter objects, with the brightest stars rated at magnitude 0 or +1. For context, the limit for visibility to the naked eye is considered to be around magnitude +6.5. Recent observations of Comet SWAN suggest a magnitude of approximately +7, just beyond naked-eye visibility in dark conditions. Nevertheless, it remains well within the reach of good binoculars.
The typical description of Comet SWAN by those using binoculars or small telescopes indicates a small, condensed head or coma, with a faint tail extending roughly two degrees.
Upcoming Visibility and Proximity to Earth
Syuichi Nakano of the Central Bureau for Astronomical Telegrams calculated the comet’s orbit based on observed positions from September 12 to 14. His findings indicate that Comet SWAN passed perihelion, its closest point to the sun, on September 12, at a distance of 46.74 million miles (75.20 million km).
As the comet moves away from the sun, it is currently approaching Earth, with its closest approach (perigee) expected on October 21, 2025, at a distance of 25.10 million miles (40.38 million km). The comet’s orbital eccentricity is approximately 0.996015, suggesting a lengthy orbital period of around 1,400 years.
Predictions regarding the comet’s brightness during its closest approach vary. Notable forecasts from Japanese comet expert Seiichi Yoshida and Dutch expert Gideon Van Buitenen indicate that it could reach magnitudes between +6 and +7. Daniel W.E. Green from the Central Bureau for Astronomical Telegrams also suggests that Comet SWAN may hover near magnitude +6 from October 2 to 20, potentially becoming faintly visible to the naked eye around October 12.
Viewing Conditions and Path Across the Sky
Currently, Comet SWAN has been primarily visible from the Southern Hemisphere. However, by the end of September, observers in the Northern Hemisphere will have a better chance to view it. The comet will ascend higher in the southwest sky, reaching an altitude of 12 degrees above the horizon at twilight’s end by early October. By October 28, it will climb to 30 degrees (“three fists”) above the south-southwest horizon after sunset.
During its passage through October, Comet SWAN will traverse across the constellations of Libra, Scorpius, Ophiuchus, Serpens, Scutum, Sagittarius, Aquila, and Aquarius.
Although many anticipate catching a glimpse of Comet SWAN, it may be challenging due to light pollution in urban areas. Observers should understand that they are looking for a diffuse object rather than a sharp star-like point. Comet SWAN is primarily composed of gas, giving it a bluish-white hue, and glows due to ultraviolet sunlight activating its gaseous components.
One common misconception circulating on social media involves the possibility of a meteor shower related to Comet SWAN around October 4 to 6. This speculation arises from diagrams showing the comet’s orbit intersecting with Earth’s orbit. Yet, as astronomer Joe Rao clarifies, the comet’s orbit lies significantly above Earth’s path, making any potential meteoroids unlikely to intersect with our planet.
While the hope for a meteor shower linked to Comet SWAN is intriguing, the likelihood is minimal given the distances involved and the comet’s gaseous composition. Observers are encouraged to enjoy the spectacle of the comet’s approach and track its journey through our night sky.