C/2023 P1 (Nishimura)

Lore & Background

Japanese amateur astronomer Hideo Nishimura discovered the comet in images taken with a 200-mm f/3 telephoto lens 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 from the previous night. At discovery, the comet was in the dawn sky, moving closer to the Sun, and had an apparent magnitude of 10–11. Pre-discovery images from PanSTARRS on 19, 24, and 25 January 2023 were identified by Robert Weryk, extending the observation arc to seven months; the comet appeared as a stellar object of magnitude about 22.

The comet brightened rapidly: by 27 August its magnitude was 7.3 with a coma 5 arcminutes across and a thin ion tail 1.5–2 degrees long. Piotr Guzik spotted it with the naked eye on 8 September at magnitude 4.7, and the tail reached up to 7.5 degrees in CCD images. On 12 September 2023 it passed 0.84 AU from Earth but was only 15 degrees from the Sun's glare. Between 1 and 14 September, the Solar Orbiter mission observed four tail disconnection events caused by coronal mass ejections. The comet reached perihelion on 17 September at 0.22 AU from the Sun, appearing briefly in the evening sky at 5 degrees above the horizon 30 minutes after sunset at 35° north latitude. Despite reaching naked-eye magnitude around +2, it was hard to locate due to solar glare. After perihelion, it was visible in STEREO's coronograph without disintegrating, and Parker Solar Probe observed it on 27–28 September 2023.

Reader's Guide

C/2023 P1 (Nishimura) is significant as a long-period comet with an outbound orbital period estimated at about 406 years, an eccentricity of 0.996, and a semi-major axis of about 57 AU, comparable to the average distance of Eris. It will not leave the Solar System, reaching aphelion in late 2226 and returning around the year 2429. The comet's legacy includes its potential link to the Sigma Hydrids meteor shower, active from November 22 to January 18 and peaking around November 30. The comet and the meteors have very similar orbits, with a small offset in perihelion. A 2024 study verified the link after orbital reconstructions of the meteors matched the comet's precovery positions nearly eight months before its discovery, though an alternative unknown comet had been proposed earlier. The comet's observation by multiple space missions—Solar Orbiter, STEREO, and Parker Solar Probe—provided unique data on its interaction with solar activity, including tail disconnection events from coronal mass ejections.

Did You Know?

• The comet was discovered by amateur astronomer Hideo Nishimura using a 200-mm f/3 telephoto lens on a Canon EOS 6D.
• Pre-discovery images from PanSTARRS in January 2023 extended the observation arc to seven months.
• A 2024 study verified the link between Comet Nishimura and the Sigma Hydrids meteor shower.