161P Hartley-IRAS

Closest to Earth: 2026 October 1 at 0.50AU
Closest to Sun: 2026 November 27 at 1.26AU

Maximum magnitude 9 during October-November 2026
possible outbursting comet.

Orbital period 21.5 years

161P Hartley-IRAS on 2026 September 9. C11 RASA + QHY163m camera. 15x30sec.

Discovered in November 1983 by Malcolm Hartley at the U.K. Schmidt Telescope, Australia and independently by the orbiting
Infrared Astronomical Satellite (IRAS), this comet has an orbital period of 21.5 years, and this will be the third observed return.

It has a relatively favourable Earth approach during the start of October, when it will be 0.5AU away and should reach magnitude 10 at this time.
It is expected to remain at magnitude 9-10 during October to November as its increasing distance to Earth is compensated by its approach to the Sun.
However, the light curve is strongly asymmetric to the perihelion.
The brightening and fading is rapid and it becomes brightest after the perihelion passage.
In 1984, there was a suspected 3 magnitude outburst, when the comet reached magnitude 7.
This outbursting activity was not recorded at its apparition in 2015.
Observers should be on the lookout for any unusual outbursts in brightness.

During October 2026, the comet will reach its maximum brightness at 9th magnitude,
as it traverses the constellations of Aquarius, Pegasus, Equuleus, Delphinus and Aquilla, well situated in the evening sky.

The first couple of weeks of October offer moon free observing.

Between October 6-8, you can find it within the “water jar” of Aquarius.

On October 14, it will be within 30’ north of Alpha Equ.

Moonlight then interferes until the evening of October 28, when the magnitude 10 comet situates about 5 degrees east of Altair (Alpha Aql)
opening up another 2 week observing window before the comet is lost to the northern skies.