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| Comet C2025 R2 (SWAN) in the constellation Aquarius Seestar S30 stack of 20x10 sec subs stacked using DeepSkyStacker. Credit: Kurt Thrust at the JPO. |
" Not one of the Jodrell Plank Observatory's finest images but last night, 31-10-2025, was not good for astro-imaging. I had to contend with cloud, wind, light pollution, a few fireworks and a waxing gibbous Moon nearby the Comet. The little Seestar S30 did well to capture enough photons to provide an Ok image after some heavy processing. All the team love to see a comet over the Jodrell Plank Observatory". - Kurt Thrust current Director of the JPO.
"At the time of image capture, the comet designated C/2025 R2 (SWAN) was at a geocentric distance on the order of 54 million km. It's line of sight movement and velocity amongst the stars in the constellation Aquarius, was significant and recognisable within a period of 30 minutes.
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| The Comet's nucleus and coma is smeared out as a line by its movement, in 30 minutes, against the fixed background stars. |
Physical and orbital characteristics
C/2025 R2 (SWAN) is a long-period comet, discovered on 11 September 2025 by amateur astronomer Vladimir Bezugly via imagery from the SWAN (Solar Wind Anisotropies) instrument aboard the SOHO spacecraft.
Its perihelion (closest approach to the Sun) occurred on 12 September 2025, at a heliocentric distance of about 0.50 AU (~75 million km).
Orbital solutions indicate rather high eccentricity (e ≈ 0.994) and a semi‐major axis on the order of tens of astronomical units, giving the comet an orbital period of several centuries to over a millennium (depending on inbound versus outbound parameters) — thus it is not a short-period, frequent visitor.
Appearance and morphology in the image
Given the distance at capture, the observed coma (the diffuse envelope of gas and dust surrounding the nucleus) is well resolved in the photograph. At such a distance, the comet’s intrinsic brightness, combined with the illuminated dust and volatile gases, yield a visible coma of perhaps several arcminutes in apparent diameter. Observers report that C/2025 R2 exhibits a faint tail extending up to ~2° under favourable conditions. This is not readily visible in our image.
The greenish hue often noted in photographs of the comet arises from diatomic carbon (C₂) and sometimes CN radicals in the coma, excited by solar ultraviolet radiation. Emission bands of C₂ and NH₂, as well as [O I] atomic oxygen lines, have been detected in spectroscopic observations of the coma.
The sunlight currently reaching the comet's nucleus and coma is somewhat diminished, when compared to perihelion, but still strong enough to sublimate ices and drive the formation of the dust and gas envelope. The tail likely points roughly anti-sunward and is shaped by solar radiation pressure (for dust) and by the solar wind/magnetic field interaction (for ion tail).
Context and significance of the capture
The image represents a snapshot in the outward leg of the comet’s passage — after perihelion and while still relatively near Earth in astronomical terms. At this distance, resolution is sufficient to reveal structural details such as the condensation of the inner coma, potential jet features (if present), and the tail’s divergence from the coma axis.
In the broader context, this comet offers an important opportunity: given its long period and recent discovery, every high-quality observation (photographic or spectroscopic) contributes to the understanding of volatile composition, dust‐to‐gas ratios, tail morphology, and how such long‐period comets evolve near perihelion and beyond". - Karl Segin outreach coordinator at the Jodrell Plank Observatory.
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| The waxing Gibbous Moon captured with the Seestar S30 just after it was used to capture the nearby Comet |
" I literally added this lunar portrait to demonstrate how a nearby Moon can impact upon the capture of less luminous deep-sky targets. The craters Copernicus, Tycho and Plato can be seen clearly, as can the major Maria and Montes Apenninus" - Joe Cairo CEO of the JPO.
