A long-tailed comet has been spotted close to the sun, and some astronomers are predicting it could be seen with the naked eye in mid-October — just as another comet is forecast to do the same. It could mean two bright comets will be visible in the night sky at the same time, on the peak night of a meteor shower.
Comet C/2025 R2 (SWAN), or SWAN R2 for short, was discovered on Sept. 12 by NASA's orbiting Solar Dynamics Observatory, whose Solar Wind Anisotropies (SWAN) instrument is used to find comets close to the sun. The previously unknown comet was found in SWAN's images by Vladimir Bezugly, a Ukrainian amateur astronomer, according to Universe Today, and it was initially called SWAN25B. Three days later, the International Astronomical Union's Minor Planet Center classified the object as a comet and renamed it C/2025 R2 (SWAN).
This long-period comet appears to orbit the sun every 22,554 years, according to EarthSky, and its tail is about the same length as five full moons.
Although SWAN R2 is still very close to the sun — passing close to Mars just after dusk, and best seen from the Southern Hemisphere, for now — that's set to change on Oct. 21, when SWAN R2 will be only 0.27 astronomical units (AU) from Earth, according to The Sky Live. That's about one-quarter the distance from Earth to the sun.
At that time, the comet could get as bright as magnitude 4, potentially making it visible to the naked eye in dark skies, even in the Northern Hemisphere. Earth may even pass through debris from the comet around Oct. 4-6, which could potentially cause a unique meteor shower. Even if it doesn't brighten sufficiently to be seen with the unaided eye, the comet should be easily visible through a pair of stargazing binoculars or a good backyard telescope.
This comet has come to light just as another comet is brightening. Discovered in January by the Mount Lemmon Survey in Arizona, Comet C/2025 A6 (Lemmon) will get closest to Earth on Oct. 21 — the same day as SWAN R2's closest approach. Comet Lemmon will be about 0.60 AU from Earth and will be visible in the morning and evening. According to Space.com, Lemmon could also get as bright as magnitude 4, which would make it possible to see with the naked eye in a dark sky.
The best nights to see both comets — if they survive their increasingly close approaches to the sun, which is not guaranteed, and they brighten as predicted — will be Oct. 20-23, when they are closest to Earth. Oct. 21 is the date of the new moon, when night skies will be free of moonlight. Oct. 20-21 is also the peak of the Orionid meteor shower, when about 20 "shooting stars" per hour are expected. You won't want to miss the prospect of two bright comets and meteors in a dark sky.
The last bright comet that was visible to the naked eye was C/2020 F3 (NEOWISE), in summer 2020, although in October 2024, Comet C/2023 A3 (Tsuchinshan-ATLAS) became visible through binoculars during a close approach to Earth.
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