C/1992 W1 (Ohshita)

Lore & Background

Nobuo Ohshita discovered C/1992 W1 using a pair of 25×150 binoculars on the night of 24 November 1992, when it was an 11th-magnitude object in the constellation Coma Berenices. His discovery was not confirmed until he photographed the comet on three subsequent nights between 28 and 30 November 1992. Precovery images taken by S. Horiguchi about three days earlier on 21 November 1992 were reported to the International Astronomical Union nearly a month later.

The comet reached perihelion on 1 November 1992 at a distance of 0.668 AU, meaning it was already on its outbound trajectory when discovered 23 days later. It made its closest approach to Earth on 23 December 1992 at a distance of 0.8181 AU. Both Brian G. Marsden and Shuichi Nakano calculated a retrograde elliptical orbit lasting 684 to 737 years, later revised to approximately 928 years, all accounting for planetary perturbations.

Orbital reconstructions in 2020 revealed that C/1992 W1 is the parent body of at least one meteor shower group, the χ-Andromedids. Another group, the January α-Ursae Majorids, have similar orbital properties, suggesting they may also originate from this comet.

Reader's Guide

C/1992 W1 (Ohshita) holds significance as the only comet discovered by Japanese astronomer Nobuo Ohshita, and its discovery using binoculars highlights the role of amateur astronomers in comet detection. The comet's orbital calculations by Brian G. Marsden and Shuichi Nakano show a retrograde elliptical orbit with a period revised from 684–737 years to approximately 928 years, demonstrating the refinement possible with planetary perturbation modeling. Its legacy extends beyond its own passage: orbital reconstructions in 2020 identified it as the parent body of the χ-Andromedids meteor shower, and possibly the January α-Ursae Majorids, linking a single comet to multiple meteor streams. The precovery images by S. Horiguchi, reported nearly a month later, underscore the collaborative nature of astronomical confirmation. The comet's perihelion before discovery and its closest approach to Earth in December 1992 provide a clear timeline of its trajectory. Overall, C/1992 W1 exemplifies how a single comet can contribute to both orbital dynamics and meteor astronomy.