C/2023 P1 Nishimura

Closest to Earth on 2023 Sep 12 at 0.84AU
Closest to Sun on 2023 Sep 17 at 0.22AU
Maximum magnitude 2 in mid-September 2023
Orbital period 437 years

C/2023 P1 Nishimura on 2023 August 29.

Confirmation image of C/2023 P1 Nishimura taken on 2023 August 14 at 20:00UT

A new amateur comet discovery!
Hideo Nishimura, Kakegawa, Japan, discovered this comet on 2023 August 12th using a Canon 6D digital camera and 200-mm telephoto lens.
This is his third discovery credit, occurring 2 years after his last find C/2021 O1 Nishimura and nearly 30 years since C/1994 N1 (Nakamura-Nishimura-Machholz).
Unfortunately, viewing circumstances were particularly poor, as it remained within 35 degrees of the Sun for several months.
In fact, it had been situated less than 40 degrees from the Sun since April 2023, which is probably why it wasn't discovered earlier.
Its highly inclined, small perihelion, retrograde orbit causes unfavourable viewing throughout its apparition.
There was a risk that the comet would not survive its perihelion approach,
however prospects improved significantly with the release of a revised orbit, which included precovery observations from PANSTARRS taken in January 2023,
which indicate that the orbit is of long period (437 years) thus the comet is not a first time visitor.

During August 2023, Southerners were able to see comet Nishimura very low in the morning sky in Gemini,
brightening from magnitude 10 to 7 before being lost to Northern hemisphere skies.
Between September 1 to 7, Northern Hemisphere observers got the best view of the comet
when it was situated in Cancer in pre-dawn skies, brightening from magnitude 6 to 4.
From September 7th, the comets solar elongation decreased rapidly, and its increasing brightness was offset by its approach into twilight.
On September 13, it reached solar conjunction at an elongation of 12 degrees, but virtually unobservable from the ground.
On September 17, it reached peak brightness of magnitude 2.0 when closest to the Sun.

The comet moved southwards after perihelion and into evening twilight.
Unfortunately the comet remained embedded in twilight for several weeks after perihelion ad was a very difficult object.
I managed an observation on September 21st at 09:00UT, estimating mag 4.0 using 25x100mm binoculars.
The comet was significantly fainter than Porrima (Gamma Vir) 3.5V
The observation was difficult due to bright twilight and atmospheric extinction

This image of C/2023 P1 Nishimura was taken on the following evening on 2023 Sep 22nd.
The comet was fading fast (approximate mag 4.5)

Comet Nishimura faded rapidly after this and maintained a poor elongation throughout October.

C/2023 P1 Nishimura on 2023 October 24 at 08:40UT.
Image taken remotely using ITEL-T70 Chile 135 mm f/3.5 Samyang Lens + CMOS. 5min. FOV 1 deg. North upper right.
Photometric (UCAC4) V mag = 9.6 tail 7' long in PA90

On November 1, the now magnitude 10 comet moves sufficiently far away from twilight to become visible in the morning sky for southerners.
During November, the comet treks slowly southwards through Centaurus, gaining altitude with each passing morning.
Moonlight no longer interferes from November 10th.
Between November 26 to 29, an interesting rendezvous occurs when the now magnitude 11.5 comet is within
2 degrees of another comet C/2021 S3 PANSTARRS, which may appear brighter at 10th magnitude.

The STEREO A spacecraft was in the perfect position to view the comet after perihelion.

It entered the field of view of the HIA1 imager from September 18 through to early October. (see chart)

You can download fits files, preferably the hires 4MB ones, choosing the correctly dated directory from the following location.


You will need to process the images.
I load the 4mb images to the free software Fitswork 4, then process using background flatten, variable flatten, calculate.