J. J. Blanpain (Marseille, France) discovered this comet in Virgo on 1819 November 28.19. The comet was then situated in the morning sky. He estimated the diameter as 6-7 arc minutes, and said a "very small and confused nucleus" was present. No tail was observed. Blanpain confirmed his find on November 29.24.
Blanpain only followed the comet until December 2, but an independent discovery was made on December 5.14, by J. L. Pons (Marlia, Italy). He described the comet as small and faint, with no tail or condensation. He continued making observations and other astronomers began to observe the comet around mid-December, with A. Bouvard (Paris, France) first detecting the comet on the 14th and P. Caturegli (Bologna, Italy) making his first observation on the 22nd. Bouvard described the comet as very faint in his 7-cm refractor. Bouvard again saw the comet in strong moonlight on the 30th and noted it was very faint. Pons obtained his final observation of the comet on the 31st, the night of full moon. He described it as very faint, but the sky clouded before he could measure its position.
As 1820 began, Bouvard and F. Carlini (Milan, Italy) were continuing observations. Bouvard's last came on the morning of the January 15, when he noted the comet was extraordinarily faint in his 7-cm refractor. Carlini obtained the last observation of the comet on January 25.14. Several other astronomers searched for the comet during January, but failed to find it. Most notably, Pons had a clear morning on the 15th, but noted the comet had entered a region containing several nebulae.
Early parabolic orbits were calculated by F. Carlini and J. F. Encke. Their resulting perihelion dates were 1819 November 17.38 and November 21.54, respectively. Encke published the first elliptical orbit in the 1824 volume of the Berliner Astronomisches Jahrbuch. Using seven positions obtained between December 14 and January 15, he determined a perihelion date of November 20.75 and a period of 4.81 years. Several other astronomers have calculated elliptical orbits over the years, with the most recent being I. Lagarde (1907). He began with the orbit computed by Encke in 1824 and revised it to better fit the seven observations obtained between December 14 and January 15. The result was an elliptical orbit with a perihelion date of November 20.85 and a period of 5.10 years.
A minor planet was discovered on 2003 November 22, by astronomers at the Catalina Sky Survey (Arizona, USA). Five images obtained with the 68-cm Schmidt telescope and a CCD camera revealed a stellar object with a magnitude ranging from 17.7 to 18.1. The object passed 2.3 million miles from Earth on December 12. At the beginning of 2004, M. Micheli integrated the orbit of this object backwards and suggested it might be identical to Blanpain's lost comet, although he revealed discordances of up to 17° in the argument of perihelion. During 2005 February, P. Jenniskens independently made the same suggestion, but showing a much better fit with discordances of only 0.2°. B. G. Marsden quickly confirmed Jenniskens' calculations and said the fit was possible with a purely gravitational solution. Although this may very well be the remnants of Blanpain's comet, the intensive backwards calculations produce a perihelion date that is 4.28 days later than that calculated from the observations made in 1819. The final resolution of this mystery may have to wait until the minor planet's orbit is refined by future observations.
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