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80P/Peters-Hartley

Past, Present, and Future Orbits by Kazuo Kinoshita

Discovery

     Christian Heinrich Friedrich Peters (Capodimonte Observatory, Naples, Italy) discovered this comet on 1846 June 26.92, in Libra. He described it as very faint, without a nucleus. He said it was very similar in appearance to a nebula situated a degree away, that was classified Herschel VI, no. 19. Peters confirmed his discovery on June 27.87 and June 28.94.
     Malcolm Hartley (U. K. Schmidt Telescope Unit, Australia) accidentally discovered this comet on a plate exposed on 1982 July 11.47 with the 1.2-m Schmidt telescope at Siding Spring. He estimated the brightness as magnitude 15 and said a faint halo was surrounding the comet's trailed image. Confirmation came on July 13.46 when the comet was photographed by observers at Perth Observatory.

Historical Highlights

APPARITION OF 1846: DISCOVERY
[Perihelion Date=1846 June 3.68; Period=7.88 years]
     Later orbits indicated the comet had already passed closest to the sun (June 3 at 1.50 AU) and closest to Earth (June 4 at 0.55 AU) before its discovery. The comet faded after discovery and was last detected on July 21.
     Using his three initial positions, Peters computed the first parabolic orbit which indicated a perihelion date of 1846 April 12.80. After observations had been extended into July, Peters revised his orbit and found a perihelion date of May 31.00. Later in the year, Heinrich Ludwig d'Arrest (Berlin, Germany) computed two different sets of parabolic elements, neither of which satisfactorily represented the observations, but did meet with success with an elliptical orbit. The perihelion date was June 1.60, and the orbital period was 15.89 years. D'Arrest revised the orbital period to 12.85 years in 1848. During 1887, with the comet already having been missed at two probable returns, Berberich used 16 positions obtained during 1846, but no planetary perturbations, and determined the period as 13.38 years. He said the period was uncertain by about one year. Berberich added that this orbit indicated the comet made close approaches to Saturn in 1856 and 1883. Another investigation took place nearly a century later when Buckley examined the 1846 positions in 1976. He applied the perturbations by seven planets and concluded the orbital period had been 12.71 years; however, he still gave an uncertainty of about three years.

APPARITION OF 1982: REDISCOVERY
[Perihelion Date=1982 May 8.57; Period=8.12 years]
     Following the comet's 1982 rediscovery, M. P. Candy (Perth, Australia) had already determined the comet was moving in an elliptical orbit by July 19 and suggested the comet was identical to the lost periodic comet Peters of 1846. Simultaneously it was announced that I. Hasegawa and S. Nakano came to similar conclusions. By July 22 the suggested link was apparently confirmed when B. G. Marsden noted that a revised orbit by Candy could be integrated backwards and arrive at a perihelion date only 10 days from that of comet Peters. He noted the orbital period was only 7.88 years in 1846.

APPARITION OF 1990
[Perihelion Date=1990 June 23.64; Period=8.13 years]
     The comet was recovered at its next expected perihelion passage in 1990. R. H. McNaught (Siding Spring Observatory, Australia) found the comet with the Uppsala Southern Schmidt telescope on 1990 May 26.44. He described the comet as diffuse and magnitude 14. The precise positions indicated the prediction required a correction of +2.0 days. The comet continued to brighten and reached magnitude 13 during the last days of May and into June. It was last seen on July 20 at magnitude 16.

APPARITION OF 1998
[Perihelion Date=1998 August 11.64; Period=8.12 years]
     The comet was next expected to arrive at perihelion on 1998 August 11 and was not expected to surpass magnitude 16 due to its unfavorable placement with respect to the Sun and Earth. It was recovered on 1998 February 16 and was only followed until April 25.

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