Copyright © 1998 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)
This CCD image was taken on 1998 May 19.52, using a 0.60-m f/6 Ritchey-Chretien telescope.
During 1983 September, Charles T. Kowal announced that an examination of photographic plates obtained during May with the 1.2-m Schmidt telescope at Palomar Observatory had revealed the appearance of a comet. The comet appeared as a diffuse, condensed trail on the three plates, which were obtained on May 8.23, 9.30, and 15.26. He estimated the magnitude as 16.
At the end of September Marsden announced that asteroid 1983 JG, which had been discovered by Zdenka Vavrova (Klet' Observatory, Czech Republic) and previously published in Minor Planet Circular 8008, was actually identical to Kowal's comet. It appeared as a trail on an image obtained on May 14.95. Vavrova did not notice any diffuseness and reported a magnitude of 16.5.
Brian G. Marsden (Central Bureau for Astronomical Telegrams) computed both a parabolic and an elliptical orbit from Kowal's initial positions, both of which indicated a large perihelion distance near 3 AU. Although he commented that this was likely a short-period comet, the short arc and large perihelion distance made the period "completely indeterminate." Marsden provided the two orbits, plus three sets of ephemerides to help astronomers track down additional images during the period of 1983 June to October. The parabolic orbit indicated a perihelion date of 1984 May 30, while the elliptical orbit indicated 1983 June 20. The elliptical orbit also indicated an orbital period of 18.80 years. Later positions indicated the period was 15.94 years.
With so many months having passed, and with so few observations available, the chances of obtaining additional observations seemed slim. However, on September 20 and 22 the IRAS satellite photographed a cometary candidate which, although very near the expected position of comet Kowal-Vavrova, was not moving at the correct speed. In an attempt to confirm the IRAS object Kenneth S. Russell took two plates with the UK Schmidt on September 28. No comet was then found. Nearly three weeks later, A. Mrkos (Klet Observatory) announced that he had found an additional image of the comet on plates taken on May 31.88. He added that this image and those of Vavrova on May 14 were definitely larger than other asteroids on the plates, with a hint of diffuseness. Mrkos' image allowed a great improvement in the orbit and Russell subsequently identified an 18th-magnitude cometary trail on his September 28 images.
Although the 1983 orbit is now well established, the IRAS images of September 20 and 22 are still a puzzle. Although the September 22 object was much closer to the expected position of Kowal-Vavrova than the September 20 object, it still lies over 15 arc minutes from the comet's expected position. In a 1986 article for the Quarterly Journal of the Royal Astronomical Society, Marsden said the IRAS observations "remain unexplained."
As the comet made its first expected return, James V. Scotti recovered it with the Spacewatch telescope at Kitt Peak on 1997 December 5 and 6. The total magnitude was given as 20.8 to 21.8 on the 5th, while the nuclear magnitude was given as 22.3 on the 6th. The precise positions indicated a prediction by S. Nakano required a correction of +5.3 days.