C/1983 J1 (Sugano–Saigusa–Fujikawa)

Lore & Background

The comet was discovered on 8 May 1983 by Matsuo Sugano, Yoshikazu Saigusa, and Shigehisa Fujikawa, who independently found it within 48 minutes. Sugano used a 15-cm reflector telescope, Saigusa a 0.20-m reflector, and Fujikawa 12×120 binoculars, estimating its magnitude at 7. The comet had already passed perihelion on 1 May and was located in Andromeda at a solar elongation of 29 degrees. It was quickly recognized that it would make a close approach to Earth, about a month after C/1983 H1 (IRAS–Araki–Alcock) passed at 0.03 AU. The comet faded slightly during May, reaching magnitude 8.3 on 20 May, then brightened in early June, with magnitude 6.6 on June 6 and a coma 15 arcminutes across. Its closest approach occurred on 12 June 1983 at 19:00 UTC at 0.063 AU, when it was visible to the naked eye at magnitude 5.5 with a diffuse coma about one degree across. After that it faded rapidly, with magnitude 7.8 on 16 June, and was last detected on 20 June.

Reader's Guide

The comet's significance lies in its extremely close approach to Earth—the fourth closest observed in the 20th century—which allowed detailed scientific observations. Radio observations by the Arecibo Observatory on 11 June 1983 revealed a very small cross section of about 0.04 km², indicating a tiny object. Infrared and visual photometry gave an effective radius of approximately 0.37 ± 0.05 km. The radio spectrum showed lines of cyanoacetylene, while infrared observations on 13 June yielded a water production rate of 1.1×10²⁸ mol/s. Notably, the abundances of NH₂, CN, C₂, and C₃ were unusually low relative to [OI] compared to other comets, and the dust/gas mass ratio was below 0.01. Regarding meteors, Robert McNaught noted that Earth would pass near the comet's orbital intersection point 2.9 days after the comet, suggesting a possible meteor shower. M. Šimek and P. Pecina recorded a small radar increase in meteors with duration less than 8 seconds on 14 June, and observed the same shower in 1984, concluding that if created by the comet, 1983 was not the first time it passed close to the Sun. This legacy ties the comet to a potential annual meteor shower, though further research was noted as needed.

Did You Know?

• The comet was discovered independently by three Japanese observers within 48 minutes on 8 May 1983.
• Its closest approach to Earth on 12 June 1983 was the fourth closest observed comet approach in the 20th century.
• The comet's effective radius was only about 0.37 km, making it a very small object.
• A possible meteor shower associated with the comet was observed by radar in both 1983 and 1984.