Copyright © 1997 by Herman Mikuz (Crni Vhr Observatory, Slovenia)
This image was obtained on 1997 December 28.73 UT with 36-cm, f/6.7 Schmidt-Cassegrain telescope, V filter and CCD. Exposure time was 5 minutes. (Image reversed by Author)
Discovery
Malcolm Hartley (U. K. Schmidt Telescope Unit, Siding Spring, Australia) discovery this comet on 1986 March 15.59. He estimated the magnitude as 17-18 and added that a faint tail was evident. Further images were obtained on March 17.68 and 20.61, whereupon the comet was annnounced to the Central Bureau for Astronomical Telegrams.
Historical Highlights
Upon the arrival of the three initial positions of this comet, Daniel W. E. Green (Central Bureau for Astronomical Telegrams) computed a "very uncertain" parabolic orbit which indicated the comet had closest to the sun on 1985 June 20 at a distance of 0.076 AU. The inclination was given as 60 degrees. Green added, "A low-inclination, short-period orbit gives similar residuals." The discovery info, as well as the rough orbit, were published on March 24. On April 8, the Central Bureau published a revised orbit which included the original positions as well as more recent ones acquired on April 5. B. G. Marsden confirmed Green's suspected short-period orbit was the correct one. His calculations indicated the comet had passed perihelion on 1985 June 5 at a distance of 0.961 AU. He said the comet's angular distance from the sun would have been too small to have permitted observations during 1985 and added that the comet appeared to have made a close approach to Jupiter during 1982. The comet remained under observation until June 7. Computations by S. Nakano during 1987 indicated a perihelion date of 1985 June 5.2, a perihelion distance of 0.9508 AU, and an orbital period of 6.27 years.
Nakano supplied a prediction for the comet's 1991 return, but searches were unsuccessful. Interestingly, on July 11 of that year, G. R. Kastel' (Institute for Theoretical Astronomy) reported that T. V. Kryachko (Majdanak) reported the discovery of a comet on images exposed on July 9 and confirmed the find on the 10th. He described it as magnitude 11, with a coma 15 arc minutes across. Nakano suggested this was Hartley 2, which indicated his prediction had been 5.6 days too late. R. E. McCrosky and C.-Y. Shao (Oak Ridge Observatory) confirmed Nakano's suggestion on July 12 when they photographed the comet with the 1.5-m reflector. The comet passed 0.77 AU from Earth around mid-August and passed perihelion on September 11. This caused it to steadily brighten throughout August and into September. The comet surpassed magnitude 10 during late July and was brighter than magnitude 9 in early August. The comet peaked near magnitude 8 during the first half of September.
The comet next passed perihelion on 1997 December 21 and was closest to Earth on 1998 January 8 (0.8177 AU). These two factors combined to cause the comet to reach its maximum brightness of about 8 at the end of December. The coma was then about 8 arc minutes across. The comet faded slowly during 1998 January. Most observers found the comet near magnitude 8.5 and about 7 arc minutes across by January 20. This comet was still being observed on 1999 April 12, when observers at the Catalina Station (Arizona, USA) determined the total magnitude as 19.2.
Additional Images
Copyright © 1997 by Masayuki Suzuki (Japan)
This image was obtained on 1997 December 21 with a 20-cm f/9 telescope and a CCD camera. Exposure time was 30 seconds. The image measures 16x12 arc minutes.
Copyright © 1998 by Stefano Sposetti
This image was obtained on 1998 January 5.73 with a 20-cm f/6.3 Celestron and a Hi-SIS22 CCD camera. It is composed of 190 20-second exposures. Sposetti colorized the image to enhance the brightness levels within the coma.
Copyright © 1998 by Masayuki Suzuki (Japan)
This image was obtained on 1998 January 25 with a 20-cm f/9 telescope and a CCD camera. Exposure time was 30 seconds. The image measures 16x12 arc minutes.
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