Copyright © 1998 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)
This CCD image was taken on 1997 March 11.71, using a 0.60-m f/6 Ritchey-Chretien telescope. (Note: Two images were put together to make this image, thus, every star appears double as a result.)
Periodic comet 94P/Russell 4 is classed as a young, dwarf comet, with a nucleus roughly 5.2 kilometers (3.2 miles) across that rotates once every 33.4 hours. It belongs to the Jupiter family of comets (comets with periods less than 20 years). The comet was discovered in 1984. Although it then had an orbital period of 6.39 years, an analysis of its orbit reveals the period had been longer in the recent past. The comet had passed 0.68 AU from Jupiter on 1975 March 6. Prior to this date, the orbital period had been 6.9 years. Prior to a close approach of 1.05 AU from Jupiter on 1938 August 6, the period had been 6.6 years. The comet has been seen at every return since its discovery.
This image is a digitized section of the actual photographic plate that the comet was discovered upon. The original plate was exposed by M. Hawkins (Siding Spring Observatory, New South Wales, Australia) on 1984 March 7.73 and, after it was developed, K. S. Russell (U. K. Schmidt Telescope Unit, Siding Spring Observatory) noted the bright diffuse trail of a comet. He estimated the magnitude as 13 and said the comet showed a noticeable tail of about 5 arc minutes in length. Immediate searches of other plates taken during the previous days revealed images of the comet had been obtained on March 2.74 and March 4.75, whereupon Russell annnounced his discovery to the Central Bureau for Astronomical Telegrams.
Brian G. Marsden (Central Bureau for Astronomical Telegrams) computed and published the first orbit for this comet on IAUC 3926 (1984 March 9). He noted that although the orbit was "rather indeterminate" from so few positions, he said "it seems likely that it is of short period." He provided a parabolic orbit with a perihelion date of 1983 December 3.25 and an elliptical orbit with a perihelion date of 1984 September 3.53 and an orbital period of 6.20 years. Further positions arrived as March progressed and by the 26th Marsden released a new orbit which indicated the comet indeed moved in a short-period orbit. From nine precise positions obtained during the period of March 2 to 22, he determined the perihelion date as 1984 January 6.60 and the orbital period of 6.37 years. He noted that the comet passed 0.6 AU from Jupiter in 1975.
The comet steadily faded after its discovery in 1984, but it was observed for a long enough period of time to enable a reliable prediction for its next return to perihelion in 1990. On December 11, 1989 J. Gibson (OAO Corporation and Jet Propulsion Laboratory, California, USA) recovered the comet using the 1.5-m reflector at Palomar Observatory. The nuclear magnitude was estimated as 19. The position indicated the prediction needed a correction of only 0.6 day.
The 1997 apparition was a very favorable return with the closest distance from Earth being 1.26 AU in late March 1997. At that time the magnitude was typically estimated as about 14.