Bright new comet discovery C/2025 R2 SWAN
C/2025 R2 SWAN
Closest to Earth: 2025 Oct 20 at 0.26AU
Closest to Sun: 2025 Sep 12 at 0.50AU
Maximum magnitude: 6.0 in late September 2025
Orbital Period: 650 years
Bright new comet discovery C/2025 R2 SWAN
On 2025 September 11, Vladimir Bezugly (Ukraine) detected a moving object in SWAN data, an ultraviolet camera onboard the SOHO satellite.
The comet was quickly confirmed on the ground by Martin
Masek (Czech Republic) who used a remote telescope located in Chile.
Martin, expecting to be searching for a small, faint patch was pleasantly
surprised by capturing such a bright comet with a long tail.
I was also notified of the new discovery and followed up
with confirmation images on September 12.41UT.
I visually observed the comet using 15x70mm binoculars, estimating it at
magnitude 7.3 with a strongly condensed but small 3’ diameter coma.
The tail was very difficult visually but easy to photograph, estimating over 2
degrees long in Position Angle 116 (eastwards).
The comet was situated near Spica in Virgo, low to the west after sunset.
After a few days of astrometric observations, a preliminary
orbit was established which indicated the comet was at perihelion,
its closest point to the Sun, on September 12 at 0.50AU. It had an unusually low
inclination of 4 degrees, close to the ecliptic plane,
and its motion is direct, indicating it is likely a periodic comet captured by
the planets.
More data will be needed to establish its precise orbital period. A dynamically
new comet this small would generally not survive.
Fortunately, the orbit indicated that the comet was still
approaching Earth and will pass 0.26 AU on 2025 October 20.
It also has an unusually small Earth MOID (minimum orbit intersection distance)
of 0.048 AU where they meet on October 3,
raising the possibility of a meteor shower on this night. The Earth crosses this
point before the comet, so I don’t expect to see any activity.
On September 16, the comet lies adjacent to Spica (Alpha virginis)
On September 20, the comet is 1.4 degrees south of Mars.
Another comet, C/2025 K1 ATLAS lies about 1 degree further south and at
magnitude 10, should make for a great photo opportunity.
On October 2, the comet lies just to the North of Alpha Librae (Zuben Elgenubi)
On the night of October 9, moonlight no longer interferes,
and the comet will be situated adjacent to star 49 Librae, on the border of
Scorpius.
You will notice it starts to pick up speed towards the Earth approach, moving
Eastwards at over 4 degrees per day.
On October 14, it lies to the south of Sabik (Eta Ophiuchii)
On October 18, it has a close approach to the Eagle Nebula Messier 16 but its rapid motion will make photographing the rendezvous challenging.
Its passage through the Milky Way will also render it more difficult to spot amongst the background stars.
By closest approach on October 20, the coma is expected to be 15’ in diameter but quite diffuse.
Coincidentally, C/2025 A6 Lemmon was also closest to Earth on this day.
Moonlight will start to interfere from October 27.
On October 29-30, it will pass 2 degrees south of magnitude 6 globular cluster M2 in Aquarius. The comet may have faded to magnitude 8 by this time.
finder charts for Sep and Oct 2025.
35 south latitude evening sky after sunset
During November 2025,
C/2025 R2 SWAN is well situated in evening skies but will fade rapidly from magnitude 8 to 11 during the month.
On November 1, you will find the magnitude 8 comet situated in Aquarius, traversing the water-jar asterism over the nights following.
From November 7, moonlight no longer interferes.
On November 11, the now magnitude 9 comet locates adjacent to Beta Piscium (Fumalsamaka)
On November 20, the now magnitude 10 comet locates slightly north of Iota Piscium
On November 27, the now magnitude 11 comet locates slightly north of Omega Piscium with moonlight starting to interfere with viewing.
