Copyright © 1997 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)
This CCD image was taken on 1996 July 15.55, using a 0.60-m f/6.0 Ritchey-Chretien telescope.
James E. Gunn (Palomar Observatory, California, USA) discovered this comet on a plate of the galaxy cluster Abell 194. The plate had been exposed on October 27, 1970 with the 122-cm Schmidt telescope. The comet appeared as a 16th-magnitude, diffuse, trailed image, which exhibited a central condensation and a small tail. The motion was slow and southwestward. Gunn made a request for confirmation to J. W. Young (Table Mountain Observatory, California, USA), but the 61-cm reflector only showed faint, threshold images near magnitude 15. A more definite confirmation had to wait until November 22 and 23, at which time J. N. Bahcall (Palomar Observatory, California, USA) used the 122-cm Schmidt to detect the comet at magnitude 16.
One decade later, prediscovery images were found on plates exposed during the Palomar Observatory Sky Survey (POSS). J. Dengel and R. Weinberger (Institut fur Astronomie, Innsbruck, Austria) discovered images of an "unidentified comet" on prints 1172. The 12-minute O exposure revealed a "small, slightly diffuse, elongated, weak spot of mean diameter ~5" and magnitude 19," while the 50-minute E exposure revealed a diffuse trail about 0.2' long, which exhibited an "extremely faint, narrow tail" extending about 1' toward PA 250°. This announcement was made on IAU Circular No. 3540 (1980 November 17). On IAU Circular No. 3588 (1981 March 31), T. Nomura (Waseda University, Tokyo, Japan) noted that this comet was "a prediscovery record of P/Gunn." These two prediscovery images are included below.
When the positions of October 27 to November 23 were received at the Central Bureau for Astronomical Telegrams, B. G. Marsden was immediately able to determine the orbit was of short-period. The prelimiary calculation revealed the period to be 6.7 years. Later revisions gave the period as 6.80 years and the perihelion date as April 19, 1969.
During early November 1980, astronomers in Austria were carefully examining plates exposed for the original Palomar Sky Survey when they spotted a comet. The comet was found on two plates exposed on 1954 August 8. The comet was described as magnitude 19, with a coma 5 arc seconds across. It exhibited a faint, narrow tail about 1 arc minute long. About 5 months later T. Nomura (Waseda University, Tokyo) identified this comet as a prediscovery image of P/Gunn.
At the comet's appearance in 1989, the maximum brightness reached a magnitude of about 12.5 during the period of May to July.
The comet next passed perihelion on 1996 July 24, making this the fifth perihelion passage since its discovery in 1970. With its closest approach to Earth coming on June 3 (1.4693 AU) of that year, circumstances were very favorable for observation. The maximum brightness reached 12th magnitude during June and July.
The comet will next pass perihelion on 2003 May 11. The comet came within visual range of the larger amateur telescopes during March of 2002, with several observers giving magnitude estimates between 14 and 15. M. Reszelski (Szamotuly, Poland) spotting it with his 0.41-m reflector on April 30 and determined the magnitude as 13.8.
Copyright © 1954 by Palomar Observatory Sky Survey (California, USA)
PREDISCOVERY IMAGES: These two images of 65P/Gunn were obtained during the Palomar Observatory Sky Survey on 1954 August 8. The left image was a 50-minute exposure on 103aE film, while the right-hand image is the 12-minute exposure on 103aO film.
Copyright © 1996 by Masayuki Suzuki (Japan)
This image was taken on 1996 July 11, using a 0.20-m f/10 LX200 telescope and a CCD camera. The image is a 30-second exposure.
Copyright © 2002 by Giovanni Sostero (Remanzacco, Italy)
This image was obtained by Giovanni Sostero on 2002 February 19.16. He used a 0.31m f/2.8 Baker-Schmidt telescope and a Hi-Sis 24 CCD camera (chip Kodak KAF0400). The comet's brightness was then given as 15.1, while the coma was 0.5 arc minute across.