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Past, Present, and Future Orbits by Kazuo Kinoshita

2MASS photo of 171P exposed on 1998 November 13
Copyright © 1998 by University of Massachusetts

This image was taken by the Two Micron All Sky Survey (2MASS) on 1998 November 13.20. It was obtained with a 3-array Near Infra-Red Camera and Multi-Object Spectrometer attached to the 1.3-m Cassegrain telescope at Cerro Tololo Inter-American Observatory in Chile. This image was obtained in the J band (1.25 Ám). Atlas Image obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.


     T. B. Spahr (University of Arizona, Arizona, USA) discovered this comet with the 0.41-m f/3 Schmidt telescope in the course of the Catalina Sky Survey on 1998 November 16.39. An additional image obtained on November 16.40 showed the comet moving northwestward. He estimated the magnitude as 16.5 and noted a round coma 18 arc seconds across. No tail was visible. Additional images were obtained on November 17, at which time the comet discovery was announced. A prediscovery image was later found on images taken by the Two Micron All Sky Survey (2MASS) on 1998 November 13.20. The J magnitude was given as 16.1.

Historical Highlights

  • The first orbit released for this comet was a parabolic one computed by B. G. Marsden (Central Bureau for Astronomical Telegrams) and published on IAU Circular 7053 (1998 November 18). Based on positions gathered during the period of 1998 November 16 to 18, he determined the perihelion date as 1999 February 20.76 and the perihelion distance as 1.58 AU. The low inclination prompted Marsden to suggest the comet was "probably of short period." On November 25 the Central Bureau issued MPEC 1998-W35. It indicated that further observations had confirmed Marsden's suggestion that the comet was moving in a short-period orbit. Based on 53 positions obtained during the period of November 16-25, Marsden determined a perihelion date of 1999 January 18.86, a perihelion distance of 1.73 AU, and an orbital period of 6.72 years.
  • Overall, CCD observations obtained during the period of 1998 November 16 to 25 indicated the comet was probably between magnitude 15.8 and 16.0, while the orbit indicated it should be brightening since it was approaching both the sun and Earth. Few physical descriptions were made during this period, but those reported indicated the coma was probably between 0.34 and 0.5 arc minutes across. By the end of 1998 December and the beginning of 1999 January, observers were estimating magnitudes near 13.5 and then the comet began fading by late January, as it moved away from both the sun and Earth. The fading and a decreasing solar elongation made observations sparse during 1999 April and the comet was last reported on April 16.15 by observers at the Catalina Station (Tucson, Arizona, USA). They gave the magnitude as 17.9.
  • Following the final observations of this comet, Patrick Rocher determined the orbit of this comet. Rocher used 265 positions obtained between 1998 November 16 and 1999 April 16 and determined the perihelion date as 1999 January 17.954, the perihelion distance as 1.726 AU, and the orbital period as 6.611 years. He estimated the period's uncertainty as ±0.0194 day.
  • Additional Images

    G. Rhemann photo of 171P exposed on 1998 December 9
    Copyright © 1998 by G. Rhemann (Austria)

    This image was taken by Gerald Rhemann on 1998 December 9.85. He used a 25.4-cm Schmidt camera. Exposure time was 10 minutes and the photographic emulsion was hypered Technical Pan 6415. The magnitude was then estimated as 14.8, while the coma was 30 arcsec across. The webmaster has cropped the image to save space. (Thanks to Gerald Rhemann for permission to use this image.)

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