C/2023 P1 (Nishimura)

C/2023 P1 (Nishimura) is a long-period comet discovered by Hideo Nishimura on 12 August 2023. The comet passed perihelion on 17 September 2023 and reached an apparent magnitude of about 2.5.

Observational history
Japanese amateur astronomer Hideo Nishimura discovered the comet in images he obtained using a 200-mm f/3 telephoto lens mounted on a Canon EOS 6D on 12 August 2023, when the comet was 1.0 AU from the Sun. He also found it in images he exposed the previous night. The comet upon discovery was located in the dawn sky and moving closer to the Sun and has been less than 50 degrees from the Sun since April 2023. Its apparent magnitude was estimated to be around 10–11. Pre-discovery images from 19, 24, and 25 January 2023 from PanSTARRS were identified by Robert Weryk extending the observation arc to seven months. The comet appeared in them as a stellar object with an apparent magnitude of about 22.

The comet brightened rapidly and by 27 August its apparent magnitude was estimated to be 7.3 and its coma to have a diameter of 5 arcminutes, while a thin ion tail 1.5–2 degrees long is visible in photographs. The comet was spotted with the naked eye by Piotr Guzik on 8 September at an estimated magnitude of 4.7. The comet tail was up to 7.5 degrees long when imaged with CCD. On 12 September 2023 the comet passed 0.84 AU from Earth but was only 15 degrees from the glare of the Sun.

On 17 September 2023 the comet came to perihelion 0.22 AU from the Sun. The comet appeared briefly in the evening sky in mid September, being 5 degrees over the horizon 30 minutes after sunset at 35° north latitude. Even though the comet reached a naked eye apparent magnitude of around +2, it was difficult to locate against the glare of the Sun. After perihelion, the comet became visible in the coronograph of STEREO, without showing signs of disintegration. The comet was also observed by Parker Solar Probe on 27-28 September 2023, during encounter 17.

Orbital characteristics
With an observation arc of seven months, the outbound orbital period of the comet is estimated to be about 406 years. An eccentricity of 0.996 gives the comet a semi-major axis of about 57 AU, which is comparable to the average distance of Eris at 68 AU. The comet will not leave the Solar System, will come to aphelion (farthest distance from the Sun) in 2227, and return around the year 2430.

Meteor shower
Comet C/2023 P1 (Nishimura) may be related to the Sigma Hydrids meteor shower that is active November 22 to January 18 (peaking around November 30).