A Halley-type comet that goes round the Sun every 21 years, at perihelion about November 2026
At its best from Georgetown with a camera until about 15 October 2026.
At its best from Georgetown with a camera until about 15 October 2026.
Tonight from Georgetown it is highest at 8:44 pm GYT, 85 degrees up in the south (almost overhead). When the sky turns fully dark at 6:50 pm it stands 61 degrees up in the east. It sinks below 20 degrees at 1:22 am. It is at least 10 degrees up for 7.2 hours of darkness.
At about magnitude 11.1 (measured) it reads 11.1 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 tonight it is a target for a camera.
From Lethem, under a dark interior sky: At its best from Lethem with a camera until about 15 October 2026. Tonight it reads 11.1 there against a camera limit of 13.9.
Face south (azimuth 180 degrees) at 8:44 pm GYT and look almost overhead, 85 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 83 degrees to the left of straight up. It is 136 degrees from the Sun in the sky and 156 degrees from the Moon, which is 3% lit.
Against the stars it moves about 385 arcseconds an hour, so it is in the same field of view all night and a little further along the next night.
A window is a run of nights on which it is at least 10 degrees up with the Sun at least 12 degrees down and its forecast brightness reaches a camera or better from Georgetown. The forecast is pinned to observers' reports from this return.
From 4 September to 28 October 2027 it is hidden in the Sun's glare from Georgetown: 55 nights.
From 21 August to 17 October 2028 it is hidden in the Sun's glare from Georgetown: 58 nights.
| In reach | Best night | Best time | Height and direction | Gear on the best night | Forecast magnitude | Nights at each rung |
|---|---|---|---|---|---|---|
| 8 October to 11 November 2026 | 8 October 2026 | 8:41 pm GYT | 85 degrees, south | Camera | about 11.1 (likely 10.4 to 11.8) | 35 camera |
Observers reporting to COBS measured it at about magnitude 11.1: the median of 10 eye estimates from 8 observers in the 10 days to 7 October 2026, ranging from 10.4 to 12.9.
The forecast is pinned to those reports and fades or brightens with distance on a slope of 15.0 magnitudes per tenfold change in Sun distance. It is good for a couple of weeks; beyond that its range widens.
On its best night from Georgetown, 8 October 2026, it could be about 11.1 (likely 10.4 to 11.8), reading 11.1 through the air. Chance of the naked eye: no real chance. Binoculars: no real chance. A small telescope: no real chance. The range is one standard deviation either side: about two forecasts in three land inside it.
Catalogue estimates, shown as a cross-check and never as how bright it will look: JPL's law gives 14.4 tonight and the Minor Planet Center's gives 9.5. 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.
Tonight: aim at azimuth 180 degrees, altitude 85 degrees, at 8:44 pm GYT. The sky is dark from 6:50 pm to 4:30 am.
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.
161P/Hartley-IRAS passes closest to the Sun (perihelion) about 27 November 2026, at 1.265 au, where 1 au is the Earth's distance from the Sun. One orbit takes 21 years. The orbit is tilted 95.8 degrees to the Earth's and its eccentricity is 0.8362 (0 is a circle, 1 an open curve).
Tonight it is 1.44 au from the Sun and 0.54 au from Earth, still approaching the Sun.
Orbit: NASA/JPL Horizons osculating elements, solution JPL#76, 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.
161P/Hartley-IRAS is a Halley-type comet that goes round the Sun every 21 years. The "P" in 161P marks a periodic comet, and the number is the order in which its return was first confirmed.
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. "Measured" means: Observers measured this in the last 10 days.
Gear rungs and ranges are estimates for a typical observer: your eyes, your sky and the night will differ.