J. L. Pons (Marseille, France) discovered this comet in Cetus during a routine search for comets on 1818 February 23.78. The comet was described as smaller than C/1817 Y1, and invisible to the naked eye. Pons commented that the comet could not be seen when the measuring device was illuminated. He added that the coma was not very extensive, but was brighter towards the middle. There was no tail. Pons also saw the comet on February 24 and 26. His final observation came on February 27.78. Two weeks of bad weather followed and Pons never saw the comet again.
J. E. Coggia (Marseille, France) discovered this comet in Hercules on 1873 November 10.84. He described it as faint and noted movement toward the southwest. He reobserved the comet on November 11.78 and described it as faint, with a central condensation. An independent discovery was made by F. A. T. Winnecke (Strasbourg, France) on November 11.73. He said the comet appeared as a pale disk 3 arc minutes in diameter and was surrounded by a pale glow. Winnecke confirmed his find on November 12.76 and said the comet was uniformly bright with a diameter of 6 arc minutes. Although the comet was observed at several other observatories as well, it was lost after November 16.73.
A. F. I. Forbes (Capetown, South Africa) discovered this comet on 1928 November 19. He gave the magnitude as about 6. The comet was confirmed by Harry Edwin Wood (Union Observatory, South Africa) on November 21.08 and the magnitude was also estimated as 6. The comet was followed by numerous major observatories until December 24. In addition, images of the comet were found on photographic plates exposed by F. Quénisset (Flammarion Observatory, Juvisy, France) on October 25 and M. Yamasaki (Mizusawa Latitude Observatory, Japan) on October 26. Yamasaki's observation was actually an earlier discovery of the comet, but bad weather and moonlight interfered with his attempts to confirm the comet until November 10, at which time nothing could be found since the comet had moved far from the previous position.
The Orbit--Part 1: The first attempt to calculate an orbit was made by J. F. Encke (1818), but every attempt left large errors. He added, "one must remain completely uncertain as to the course of this body." Years later, both Pogson (1850) and J. R. Hind (1872) were able to produce rough parabolic orbits with perihelion dates of 1818 February 7.90 and February 3.72, respectively. Hind noted that the ascending node was close to that of the orbit of Biela's comet. He then took the orbits of Biela's comet for 1772 and 1826 and tried to apply them to the path of the 1818 comet. In each case he noted that the comet was too far from perihelion and too far removed in latitude. Hind finally concluded, "These large differences appear conclusive against the idea of a possible connexion of the first Comet of 1818 and the Comet of Biela." Despite Hind's conclusion, E. Weiss (1873) became intrigued by the orbit of this comet and, in particular, the orbit determined by Pogson. He also mentioned the possibility that this comet might have been part of comet 3D/Biela at one time.
The Orbit--Part 2: Upon the comet's accidental rediscovery in 1873, E. Weiss and J. R. Hind took positions spanning the period of November 11, 12, and 13, and independently calculated the first orbits. Weiss determined a perihelion date of 1873 December 4.60, while Hind gave it as November 30.78. Both astronomers noted the similarity between this comet's orbit and that of Pons' comet of February 1818. Additional orbits were calculated by W. Fabritius and Weiss (1874), which indicated a perihelion date of December 1.7. F. W. A. Argelander also commented on the similarity of Fabritius' orbit and that of the comet of February 1818. Weiss found that by assigning a perihelion date of 1818 February 7.10 to his orbit, the first and last rough positions of Pons' 1818 comet were closely represented. He determined two hypothetical elliptical orbits, the first had a perihelion date of December 2.09 and a period of 55.82 years, while the second had a perihelion date of December 3.44 and a period of 6.98 years. Two years later, Weiss published a revised set of possible elliptical orbits indicating possible periods of 55.82, 18.61, and 6.20 years. L. Schulhof also joined in to establish a link between the 1818 and 1873 comets. In 1885, he suggested periods of 7, 9.3, or 55.8 years were most likely. He said the 7-year period would cause the comet to pass 0.18 AU from Jupiter during March of 1841. The 9.3-year period would bring up the possibility that Pons' comet seen during September 1808 could be an early appearance. If the 56-year period were true, then comet C/1457 A1 could be an earlier apparition. Schulhof (1886) more precisely determined orbits with periods of 6.20 years and 55.82 years. He published additional investigations in 1887 and 1892, but the 1818 and 1873 observations were just too rough and he never derived the correct period.
The Orbit--Part 3: Using precise positions obtained during November 21 to 24, Andrew Claude de la Cherois Crommelin obtained the first orbit for the 1928 comet, which revealed a very close similarity to the comets of 1818 (Pons) and 1873 (Coggia-Winnecke). He said, "The period may be either 55 years or some sub-multiple of this." Charles Hugh Smiley obtained very similar elements and also pointed out the similarity to the comets of 1818 and 1873. Following the acquisition of his December 20 precise position, Wood was able to calculate an elliptical orbit which gave a period of 28.66 years. Thiele used three precise positions obtained between November 24 and December 10, and published an orbit on January 18, 1929, which gave the perihelion date as 1928 November 4.99 and an orbital period of 32.28 years. He commented that, in view of Crommelin and Smiley's undoubted link of this comet to the comets of 1818 and 1873, his orbit gives support to an orbital period of 27.5 years rather than the suggested 55 years. During February 1930, Crommelin took three positions obtained between October 25 and December 16, and computed a refined elliptical orbit. The perihelion date was determined as November 4.95 and the orbital period was 27.90 years.
1956 Apparition: This was the first predicted return of this comet. During 1930, Crommelin took positions from the three apparitions and included planetary perturbations to determine the comet's next perihelion date as 1956 October 3.7. During 1932, Crommelin revised his calculations using perturbations calculated using shorter time intervals and concluded the next perihelion date would occur on October 8. During 1955, M. P. Candy and J. G. Porter successfully linked the three apparitions and then applied perturbations from Venus to Neptune "where appreciable." The result was a perihelion date of October 19.37. L. Pajdusáková (Skalnaté Pleso Observatory, Slovakia) recovered this comet on 1956 September 29.99. She estimated the magnitude as 10, and said the comet was diffuse, with a central condensation. A. Mrkos (Lomnicky Stít, Slovakia) photographed the comet on September 30.13 and September 30.14, and measured positions that indicated the comet's perihelion date was less than six days later than that predicted by Candy and Porter. The comet was apparently at its brightest in early November, when brightness estimates were about 7.3. The comet was last detected on November 29.32, when exposures of one and two minutes were obtained by D. McLeish (Bosque Alegre Observatory, Argentina) using the 152-cm reflector.
1984 Apparition: Independent predictions by S. Nakano and B. G. Marsden indicated the comet would pass perihelion on 1984 February 20.19. The comet was recovered by L. Kohoutek (German-Spanish Astronomical Center, Calar Alto, Spain) on 1983 August 9.01, at a position indicating the predictions were only 0.02 day off. Kohoutek was using the 80-cm Hamburg Schmidt telescope and gave the nuclear magnitude as 20. Kohoutek obtained additional photographs with the same telescope on August 9.04 and August 10.00. He noted the comet had a stellar appearance. The comet was brightest during late February and early March of 1984, when visual observers reported maximum magnitudes of 8.2-8.5.The coma diameter was within the range of 3.5' to 8.0' and there was a short tail. The comet was last detected on May 27.35 and May 27.40, when A. C. Gilmore (Mt. John University Observatory, New Zealand) obtained two 60-minute exposures using the Boller & Chivens 61-cm reflector. No physical description was provided.
2011 Apparition: During 2003, K. Kinoshita took positions from the apparitions spanning the period of 1818 to 1984, included planetary perturbations, and solved for nongravitational effects. He predicted the next perihelion date as 2011 August 3.81. During 2008, S. Nakano took positions from the apparitions spanning 1873 to 1984, included planetary perturbations, and solved for nongravitational effects. He predicted the next perihelion date as August 3.80.
Close approaches to planets: This comet made five close approaches to Earth during the 19th and 20th centuries, but there are no close approaches to planets during the 21st century. (From the orbital work of Kazuo Kinoshita)
- 0.66 AU from Earth on 1818 March 9 (contributed to comet's first discovery)
- 0.22 AU from Earth on 1873 November 17 (contributed to comet's second discovery)
- 0.47 AU from Earth on 1928 October 10 (contributed to comet's third discovery)
- 0.62 AU from Earth on 1956 September 28
- 0.79 AU from Earth on 1984 March 23