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206P/Barnard-Boattini

Image of D/1892 T1 exposed on 1892 October 13
Copyright 1892 by E. E. Barnard (Lick Observatory, California, USA)

This is a small portion of the image exposed for 4 hours and 20 minutes by E. E. Barnard on 1892 October 13 and is the first photographic discovery of a comet. Barnard was using the 15-cm Willard lens and was photographing the Milky Way west of the star Altair. The comet trailed during the exposure and the white arrows mark the ends of the trail in the star rich field. [This image was photocopied from the 1893 February issue of The Observatory.]

Discovery

This comet marked the beginning of a new era in cometary astronomy, as it was the first to be discovered by photography. Shortly after darkness fell on 1892 October 13, E. E. Barnard (Lick Observatory, California USA) aimed the 15-cm Willard lens at the Milky Way west of the star Alpha Aquilae (Altair) and exposed a photographic plate for 4 hours and 20 minutes. The lens had been guided to counter the affect of Earth's rotation, which resulted in the stars appearing as sharp dots on the plate. He immediately developed the plate and quickly noticed a "distinct hazy trail near the middle of it, and about a quarter of a degree long." Unfortunately, that area of the sky was then too near the horizon to make a search worthwhile. As soon as it got dark the next evening, Barnard looked for the object with the 30-cm refractor and found a very faint, diffuse object about a degree southeast of the position on the photograph. Barnard estimated the magnitude as about 13, and noted the comet was round, with little central condensation.

Historical Highlights

  • The comet had passed closest to Earth about a week before discovery, but was still heading toward perihelion. J. Palisa (Vienna, Austria) described it as faint, with a nucleus on October 16. G. Bigourdan (Paris, France) said the diffuse, round comet was very faint on the 17th, with a brightness of 13.3-13.4. He noted that the coma was 40-50 arc seconds across, with a central condensation. R. Schorr (Hamburg, Germany) said the comet seemed to contain several nuclear points on the 17th and 18th. C. F. Pechüle (Copenhagen, Denmark) described the comet as small and faint on the 18th. H. C. Wilson (Goodsell Observatory, Minnesota) saw the comet with a 41-cm refractor on the 21st and described it as faint and round, with a diameter of 1'. He added that it was centrally condensed and contained a nucleus of magnitude 12. Wilson added that the comet was barely visible in the 13-cm finder. Wilson was no longer able to find the comet thereafter. Palisa said the comet was very faint on October 27 and exceptionally faint on November 7. Barnard said the comet appeared excessively faint and difficult to see in the 30-cm refractor on the 8th. He added, "It is scarcely probable this object can be followed very much longer." Palisa said the comet was exceptionally difficult to see on the 9th and 13th. On November 22, Barnard said the comet was "excessively faint and diluted," as seen in the 30-cm refractor. He added, "Further observations will be impossible." The comet was last detected on December 8.80, when S. Javelle (Nice, France) located it with the 76-cm refractor.
  • The first parabolic orbit was calculated by W. W. Campbell. He used positions obtained on October 16, 17, and 18, and determined the perihelion date as 1892 August 26.64. He said the orbit was "naturally uncertain." During the next few weeks calculations were published by R. Schorr, G. E. Whitaker, and L. Schulhof which revealed perihelion dates in the range of November 21 to 28. Campbell then published a revised orbit using positions spanning the period of October 14 to 26. The resulting perihelion date was December 3.10, and he noted that some of the residuals were large and that a recalculation failed to reduce it. Campbell suggested that this fact, "taken in connection with the direct motion, and the fairly small inclination, points strongly to an elliptic orbit."
  • The first elliptical orbit was calculated by C. N. A. Krueger. Using positions spanning the period of October 16 to 25, he determined the perihelion date as December 7.75 and the period as 10.38 years. Additional elliptical orbits were calculated by Schulhof, Krueger, J. R. Hind, J. G. Porter, and J. Coniel. Each astronomer found a perihelion date on December 11, but while Krueger and Porter found a period between 6.2 to 6.3 years, Hind gave it as 6.63 years, and Coniel gave three orbits with periods of 6.23, 6.52, and 6.84 years.
  • The comet was lost for over a century, despite predictions in 1899, 1905, and later. The last investigation into the orbit was published by D. K. Yeomans (1975). He took 40 positions spanning the entire period of visibility and gave the period as 6.52 years. Yeomans indicated the period had a probable error of about two weeks.
  • A. Boattini (Catalina Sky Survey) discovered a comet on a CCD image obtained with the 68-cm reflector on 2008 October 7.22. The magnitude was estimated as 17.5. Fourteen additional images were obtained with the same telescope between October 7.23 and October 7.35. The magnitude estimates obtained during this period ranged from 17.1 to 18.6. Using 69 positions reported during October 7 and 8, B. G. Marsden calculated an elliptical orbit with a perihelion date of 2008 October 25.01 and a period of 5.92 years. M. Meyer (Limburg, Germany) independently calculated an orbit and then backwards integrated it. He found a remarkable similarity to comet D/1892 T1 (Barnard 3) which had been lost since its discovery appartion. Meyer reported the possible link to the Central Bureau and both G. V. Williams and S. Nakano confirmed the identity.
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