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D/1894 F1 (Denning)

Discovery

W. F. Denning (Bristol, England) was conducting a routine sweep for comets when he found this faint object on 1894 March 26.90. The comet was then over a month and a half passed its closest approach to both the sun and Earth.

Historical Highlights

  • The comet was most observed on March 28, when the total magnitude was given as about 11. B. von Engelhardt's (Dresden, Germany) noted a stellar nucleus of magnitude 13-14 and noted the comet was not visible in the 13-cm finder. Observers generally described the coma as fan-shaped, with the nucleus being in the northern portion. The overall diameter was 1-2 arc minutes. K. Oertel (Munich, Germany) said the coma appeared granular in the 27-cm refractor. The tail was said to extend toward PA 165° by J. Hartmann (Leipzig, Germany) and toward PA 150° by L. Boss (Dudley Observatory, New York). Boss gave the tail length as 5 arc minutes, while E. Millosevich (Rome, Italy) gave it as 3 arc minutes.
  • Numerous observations were made during the remainder of March. Both Engelhardt and G. Le Cadet (Lyon, Germany) specifically noted a stellar nucleus of magnitude 12.5 on March 29, while Engelhardt and H. C. Wilson (Goodsell Observatory, Minnesota, USA) independently noted that the comet was perceptible in their 13-cm finders on the same evening. A. Kammermann (Geneva, Switzerland) said the coma was shaped like a parabola and Wilson said the tail was 2 arc minutes long. On March 30, F. Ristenpart (Göttingen, Germany) gave the total magnitude as 9-10 and noted a coma diameter of 45 arc seconds, while Engelhardt described the comet as faint, elongated, and diffuse, with a condensation and a stellar nucleus. On March 31, C. F. Pechüle (Copenhagen, Denmark) noted a condensed nebulosity extending toward about PA 100°.
  • On April 1, Engelhardt described the comet as very faint, diffuse, elongated, and condensed. On the 2nd, I. Benko von Boinik (Pula, Yugoslavia) gave the magnitude as 11.0 and estimated the coma as 5 arc minutes across and the condensation as 1 arc minute across. That same evening, Wilson said the tail extended toward PA 170.2°. On the 7th, J. Guillaume (Lyon, France) said the magnitude was 11 and the stellar nucleus was magnitude 12-13, while Ristenpart said the comet was so faint, that it sometimes disappeared. That same night, Oertel said the comet appeared extremely faint. O. Knopf (Jena, Germany) said the comet was at the limit of visibility on the 8th. On the 21st, F. Renz (Pulkovo Observatory, Russia) said the comet was very faint and appeared as a small, pale nebula, with recognizable condensation. On the 22nd, Renz described the comet as a faint, oblong nebulosity, whose northern section was condensed. Ristenpart was unable to see the comet with the 15-cm refractor on the 23rd, while H. A. Kobold (Strasbourg, France) observed with the 46-cm refractor and described the comet as rather small, with a nucleus of magnitude 12. He said the coma extended like a tail. Schorr could not see the comet with the 26-cm refractor on the 25th.
  • Although a few observatories were still measuring the comet's position during May and into June, the only physical description came from Kobold on May 5, when he simply noted the comet was very small and faint. The comet was last detected on June 5.92, when S. Javelle (Nice, France) found it with a 76-cm refractor.
  • The first parabolic orbit was calculated by L. Schulhof using positions from March 27, 29, and 31. He determined the perihelion date as 1894 February 13.70. L. Boss took positions spanning the period of March 28 to April 2 and determined the perihelion date as February 17.77. He wrote, "The computations indicate possible eccentricity." Additional parabolic orbits were published by Schulhof, Boss, and C. N. A. Krueger during the next few weeks, which seemed to isolate the perihelion date as February 14. Schulhof began suspecting a deviation from parabolic motion in the April 16 issue of the Astronomische Nachrichten.
  • The first elliptical orbit was calculated by Schulhof using positions spanning the period of March 27 to April 25. It indicated a perihelion date of February 9.58 and a period of 6.74 years. Later calculations would reveal the general correctness of this early elliptical orbit, but there continued to be some descrepancy in the period. During the next few weeks the period was given as 7.94 years by Boss, 6.79 years by Schulhof, 6.76 years by J. R. Hind, and 7.70 years by Hind. Several months after the comet was last seen, Schulhof calculated a couple of likely orbits, but still considered the uncertainty in each as +/-30 days. The resulting periods were 7.42 years and 7.55 years.
  • As orbits were computed for this comet, Hind and Lamp suggested this comet might be the lost comet Brorsen. Schulhof concluded that the comets could not be identical, but said it was probable they came from the same source.
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