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125P/Spacewatch

Past, Present, and Future Orbits by Kazuo Kinoshita

A. Nakamura image of 125P exposed on 1996 July 15
Copyrightę1996 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)

This CCD image was taken on 1996 July 15.51, 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.)

Discovery

     This comet was discovered in Aquarius by Tom Gehrels (Steward Observatory, Arizona, USA) on CCD images obtained with the 0.91-m Spacewatch telescope on 1991 September 8.26. Then situated 1.70 AU from Earth, the comet had been closest to Earth in August (1.64 AU). Scotti measured the initial position and determined the nuclear magnitude as 21.1 on September 8.28. Further images were obtained on September 9, with the nuclear magnitude being determined as 20.9. Scotti described the condensation as essentially stellar, while a tail extended more than 5 arc minutes towards PA 258°. This comet holds the distinction of being the faintest comet ever discovered.

Historical Highlights

  • The comet was kept under observation until 1991 November 9.20, when B. E. A. Mueller (Kitt Peak Observatory, Arizona, USA) photographed it with a 2.1-m reflector. The comet was then situated 2.50 AU from Earth and 3.03 AU from the sun. The nuclear magnitude was determined as 22.0.
  • Using 15 positions obtained during the period of 1991 September 8 to 12, B. G. Marsden computed a parabolic and elliptical orbit and said the positions were satisfied "comparably well." The parabolic orbit indicated a perihelion date of 1991 December 8.45, and a perihelion distance of 0.526 AU. The elliptical orbit indicated a perihelion date of 1990 December 18.45, a perihelion distance of 1.535 AU, and an orbital period of 5.58 years. Shortly after mid-September, Marsden confirmed the elliptical orbit was correct and by mid-October he determined a perihelion date of 1990 December 22.27, a perihelion distance of 1.541 AU, and an orbital period of 5.59 years.
  • The comet next passed perihelion on 1996 July 14.59. It was recovered by T. Seki (Geisei, Japan) on 1996 March 11.58 and was last detected on 1996 September 2.45 by A. Nakamura (Kuma Kogen Astronomical Observatory, Japan). Although the comet was not expected to exceed magnitude 16 during this apparition, it experienced an outburst during the second half of July 1996 during which time the magnitude nearly reached 14.5.
  • The comet was next passed perihelion on 2002 January 28.05. It was recovered on 2002 March 12.84 at Toyonaka and was last detected on 2002 September 4.35 by the Near-Earth Asteroid Tracking survey at Palomar Observatory (California, USA). The maximum magnitude reached about 18 during March of 2002.
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