A long-period comet, at perihelion about July 2027
Not in reach from Georgetown on this return: it is too faint for a camera here.
Not in reach from Georgetown on this return: it is too faint for a camera here.
Tonight from Georgetown it is highest at 9:21 pm GYT, 55 degrees up in the south (halfway up). When the sky turns fully dark at 6:50 pm it stands 39 degrees up in the south-east. It sinks below 20 degrees at 1:32 am. It is at least 10 degrees up for 7.5 hours of darkness.
At about magnitude 18.4 (last reported) it reads 18.5 through the air at that height. From Georgetown's sky, where the faintest star overhead is about magnitude 4.3, a comet has to read 3.3 for the naked eye, 6.8 for binoculars, 8.4 for a small telescope and 12.1 for a camera. So it is out of reach tonight.
From Lethem, under a dark interior sky: First in reach from Lethem about 19 June to 28 July 2027, with a camera.
Face south (azimuth 180 degrees) at 9:21 pm GYT and look halfway up, 55 degrees above the horizon. A fist held at arm's length covers about 10 degrees.
A comet's gas tail points away from the Sun: at that minute the anti-Sun direction leans 49 degrees to the left of straight up. It is 132 degrees from the Sun in the sky and 147 degrees from the Moon, which is 3% lit.
Against the stars it moves about 56 arcseconds an hour, so it is in the same field of view all night and a little further along the next night.
It was last reported to COBS on 16 September 2026, at about magnitude 18.4 (1 report in 30 days). That is too few, or too long ago, to call it measured: it may have changed.
No one has followed this comet through a return like this one, so the forecast is a catalogue estimate with a wide range. It looks like a first-time visitor from the outer Solar System, and those usually brighten more slowly than their early numbers suggest.
Catalogue estimates, shown as a cross-check and never as how bright it will look: JPL's law gives 18.0 tonight and the Minor Planet Center's gives 20.8. Catalogue laws missed this season's measured comets by 2 to 4.5 magnitudes.
A comet's light is spread over a fuzzy patch, so it is harder to see than a star of the same magnitude. That is why the gear rungs ask for a magnitude in hand.
On a fixed tripod keep each exposure short enough that the stars stay round, then stack many frames. For a long stack, align on the comet as well as on the stars: it drifts against them from frame to frame. A dark site adds more than any lens.
C/2026 O1 (PANSTARRS) passes closest to the Sun (perihelion) about 18 July 2027, at 1.500 au, where 1 au is the Earth's distance from the Sun. Its orbit is so stretched that it will not return in our lifetimes. The orbit is tilted 137.3 degrees to the Earth's and its eccentricity is 1.0008 (0 is a circle, 1 an open curve).
Tonight it is 3.80 au from the Sun and 3.06 au from Earth, still approaching the Sun.
Orbit: NASA/JPL Horizons osculating elements, solution JPL#6, retrieved 8 October 2026. Positions on this page are computed from them in your browser and agree with JPL's own tables to half an arcminute.
C/2026 O1 (PANSTARRS) is a long-period comet. The "C/" marks a comet that is not known to return within 200 years; the year and letters record when it was found.
Orbits: NASA/JPL Horizons (Giorgini, JD and the JPL Solar System Dynamics Group), data retrieved 2026-10-08.
Catalogue brightness laws: JPL Small-Body Database and the IAU Minor Planet Center.
Observed brightness: COBS Comet Observation Database (https://cobs.si) and its contributing observers, CC BY-NC-SA 4.0.
Data updated 8 October 2026. "Recent" means: Last measured within the past month. It may have changed.
Gear rungs and ranges are estimates for a typical observer: your eyes, your sky and the night will differ.