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205P/Giacobini

Discovery

Michel Giacobini (Nice Observatory, France) discovered this comet in Serpens on 1896 September 4.84. He described it as a faint, circular object about 1' across. F. Sy (Algiers Observatory) was the first to confirm the comet. On September 5.82, he described it as faint, about 30" across, and with a central condensation. W. A. Villiger (Germany) independently confirmed the comet on September 5.83. He observed with a 27-cm refractor and determined the total magnitude as 11.3. He added that the coma was 1' across and contained a sharp nucleus.

Historical Highlights

  • The comet was well observed during the remainder of September. H. J. A. Perrotin (Nice Observatory) observed the comet on September 6 and described it as faint. Several astronomers observed the comet on September 7. A. Abetti (Arcetri, Italy) found the comet small and faint. G. Le Cadet (Lyon, France) said the comet was faint and nearly round in the 32-cm refractor. H. A. Kobold (Strassburg) observed with a 46-cm refractor and said the comet appeared "small, round, and rather faint, with a small condensation." He added that the nucleus was magnitude 12. On September 8, R. Schorr (Hamburg Observatory, Bergedorf, Germany) described the comet as small and extraordinarily faint, while Abetti said it was small and faint. On September 10, Sy observed with the 32-cm refractor and said the comet seemed elongated toward PA 160°. On September 11, Le Cadet described the comet as faint and nearly round.
  • Beginning on September 26, the first of a series of observations were made indicating the comet had split. On that date, Perrotin detected an extremely faint companion very near the main nucleus while using the 76-cm refractor. Perrotin observed the secondary nucleus the next two nights, but these remain the only direct observations of a secondary nucleus. There were, however, some additional observations by others which certainly suggest something did happen to the comet. The first such observations were rather cautious reports of a second condensation within the coma by Perrine and Hussey of Lick Observatory on September 30 and October 1. They were using the 91-cm refractor. Sy reported the nucleus appeared elongated when he observed the comet on October 10 with a 32-cm refractor. Interestingly, the position angle given by Sy significantly differed from Perrotin's and many past researchers have ignored it; however, in 1978, Z. Sekanina examined the comet's motion and its earth-sun orientation and concluded that the "position angle of the companion should have changed rapidly with time." Based on the available information Sekanina concluded the comet's nucleus had split on 1896 April 24.
  • For the remainder of the comet's apparition, the number of observers quickly declined as the comet continued to grow fainter. Perrotin reported that his observations on October 5 and 8 revealed the comet was so faint it was at the limit of his telescope. The comet attained its most southerly declination of -14° on November 3. Kobold observed with the 46-cm refractor on November 7 and said the comet appeared as a very faint, diffuse nebulosity, with a central condensation. The comet was last observed on 1897 January 5.18, when W. J. Hussey (Lick Observatory) saw it with the 91-cm refractor.
  • The first parabolic orbit was calculated by H. C. F. Kreutz using positions spanning the period of September 5 to 7. The perihelion date was 1896 October 8.47. Additional calculations by Giacobini, Kreutz, and Perrotin during the next few weeks established the perihelion date as October 17.55.
  • The first elliptical orbit was calculated by Perrotin and Giacobini using positions spanning the period of September 4 to 27. They determined the perihelion date as October 28.80 and the period as 6.55 years. Additional calculations by W. J. Hussey, Perrotin, and C. W. L. M. Ebell (1903) eventually established the perihelion date as October 28.54 and the period as 6.65 years.
  • This comet was not seen again for over a century, but was finally rediscovered by Koichi Itagaki (Yamagata, Japan) on 2008 September 10.57, in the course of his routine supernova search program. The images were obtained with his 60-cm reflector and CCD camera and revealed the magnitude as 13.5. About five hours after the object had been posted on the Near-Earth Object Comfirmation page of the Harvard-Smithsonian Center for Astrophysics, Maik Meyer (Germany) made the suggestion that this new object was identical to D/1896 R2 (Giacobini), which had been lost since its discovery apparition. One of the people he directly informed was Syuichi Nakano (Japan), who quickly confirmed the link.
  • New companions were announced by D. T. Durig and K. N. Hatchett (Cordell-Lorenz Observatory, Sewanee, Tennessee, USA). They found two faint companions moving in the same direction as the main comet and as the same speed on September 22. A recheck of their images revealed the companion nearest the main comet had also been photographed on September 17. The main comet is now formally known as fragment "A", the closest fragment is now fragment "B", while the more distant object is fragment "C". Fragment "B" is about four magnitudes fainter than "A", while "C" is five magnitudes fainter than "A".
  • cometography.com