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C/1956 R1 (Arend-Roland)

Paranal Observatory photo of C/2001 A2 exposed on 2001 May 16
Copyright © 2001 by Paal Brekke

This image was obtained by Kjell Brekke at the Oslo Solar Observatory (Harestua, Norway) on 1957 April 25.97. (Special thanks to Paal Brekke (NASA Goddard Space Flight Center) for permission to use this picture.)


     Sylvain Arend and Georges Roland (Royal Observatory, Uccle, Belgium) discovered this comet on a 50-minute minor planet survey exposure obtained with the 40-cm f/5 double astrograph on 1956 November 8.93. Arend and Roland estimated the magnitude as 10, and said the comet was diffuse, with a central condensation. The comet was also found on a 61-minute 30-second exposure obtained with the same telescope on November 8.94. The daily motion was given as -2m 18s in RA and -0° 18' in DECL. These images were not found until over one week after the photographs were exposed and confirmation could not be obtained until November 20.83, when Arend obtained a 10-minute exposure with the double astrograph. Arend estimated the magnitude as 12.0.

     S. Kaho (Tokyo Observatory, Konko station) later found a prediscovery image of the comet on a plate he had exposed for variable stars on November 7.6.

Historical Highlights

  • After the announcement of the comet's discovery, observations began elsewhere on November 21. Magnitude estimates for the remainder of the year changed slowly, with estimates around 11 during the remainder of November and around 10 by the end of December. The tail seems to have been first detected on November 27, when Max Beyer (Hamburg-Bergedorf, Germany) visually detected it and said it was 4 arc minutes long, while K. Wenske (Hamburg-Rahlstedt, Germany) photographed the comet with a 190-mm Schmidt and said the tail was 2 arc minutes long. By the end of December the tail was extending at least 8 arc minutes. On November 28, Potter (Goethe Link Observatory, Indiana University, Indiana, USA) described the comet as diffuse, with a condensation. During December numerous magnitude determinations were being made of the nucleus. These typically ranged from 12.6 to 12.9.
  • The comet was about magnitude 10 at the beginning of 1957 January. It continued to slowly brighten as this month progressed and was slightly brighter than 9 by month's end. Most observers indicated the tail length remained near 10 arc minutes for the entire month. The coma remained diffuse and about 1 arc minute across. It contained a stellar nucleus that slowly brightened to magnitude 12.3 by month's end. On January 26, R. L. Waterfield commented, "The tail can be traced for at least half a degree in P. A. 50° and is slightly fan-shaped." He added that the coma was heavily condensed so that an inner coma was 30 arc seconds across and an outer coma was 1 arc minutes across.
  • The comet had been steadily moving away from Earth since its discovery and reached its greatest distance on February 4 (1.9432 AU). The comet was still at magnitude 9 when the month began, but with the distances from the sun and Earth decreasing after the 4th, it began to quickly brighten and was actually about magnitude 7.5 when last seen at low altitude on February 28. No estimates of the coma diameter were apparently made during the month, but the stellar nucleus did brighten to 11.5. The photographic tail length was consistently near 30 arc minutes, while visual observers were still seeing a length of only 5 to 10 arc minutes.
  • The last observation of February, when the comet was only 25 degrees from the sun, was also the last observation of the comet prior to its first conjunction with the sun. The comet passed only 13.7 degrees from the sun on March 20. At the beginning of April the comet's motion changed from a strong southerly motion to a strong northerly motion in about 3 days. It was finally recovered on April 2.7, when John Graham Gow (New Zealand) described the comet as "little, if any, brighter than Beta Ceti," which Karl August Thernoe said indicated a magnitude of about 2.0. The comet was then 18 degrees from the sun.
  • Southern Hemisphere astornomers scrambled to observe the comet at this point, as a very small window existed with which to see the comet before it was again lost in the sun's glare prior to its second conjunction with the sun. A French Antarctic Expedition at Adelie Land saw the comet on April 6 and said the tail extended 3-5 degrees. Interestingly, K. Gottlieb and Antoni Przybylski (Mount Stromlo Observatory, Canberra, Australia) obtained a large scale photograph on April 10, which suggested the nucleus was double with a separation of about 9 arc seconds. The comet was last detected prior to its second conjunction with the sun on April 13, when Gottlieb and Przybylski estimated the magnitude as not brighter than 1. The comet was then about 10 degrees from the sun and it passed only 5.2 degrees away on April 16. The comet passed closest to Earth (0.5691 AU) on April 20, and was recovered exiting twilight on April 21, when it was 21 degrees from the sun. Josef Hopmann and A. Purgathofer (University Observatory, Vienna) then estimated the magnitude as 2, while Beyer determined it as 1.00. The Vienna observers added that the nucleus was 8 arc seconds across, while the coma was over 3 arc minutes across. Beyer said the tail extended 2.5 degrees.
  • The comet was nicely observed as it exited evening twilight and was moved northward. Magnitude estimates fell from about 1.5 on April 22 to 2.7 by the 30th. The nucleus was brilliant with magnitude estimates ranging from 4.5 to 6. Observers reported the comet and nucleus were distinctly yellowish. Most notable was the appearance of a bright anti-tail (tail pointing toward the sun) in addition to its normal tail. On April 22, R. Fogelquist (Uppsala Observatory, Sweden) photographed a main tail extending about 25 degrees and a sunward tail extending 13 degrees. On April 23, Beyer said the main tail was 15 degrees long, while the anti-tail extended 8 degrees. By the 25th Fogelquist said the sunward tail was spearlike in appearance, but "was unsymmetrically surrounded by an ellipsoidal envelope of a greatest width of nearly 3 degrees." To the naked eye the sunward tail was about 15 degrees long, while the main tail was about 30 degrees long. By the 26th, several observers remarked on the fading or even total disappearance of the anti-tail. Beyer said the anti-tail had become weaker, while Fogelquist observed without optical aid and said the anti-tail was no longer visible. By month's end, those still observing the anti-tail saw it extending less than one-half degree. Interestingly, on the 27th Dommanget said the nucleus looked like a very close double star, with it being elongated towards PA 110 degrees, and the "distance of separation" being 2.2 arc seconds.
  • The comet started out near 3rd magnitude as May began, but fell to 7.2 by month's end. This rapid fading was brought about by a steady motion away from both the sun and Earth. Traces of the anti-tail were still reported by Caprioli and Gialanella on May 2, but it was apparently not detected thereafter. The nucleus faded from magnitude 7 to near 11 as the month progressed. The main tail had shrunk to only 7 degrees by the 3rd and continued to decrease thereafter. By mid-month numerous observers were estimating its length as 2 to 3 degrees long, while estimates at the end of the month were about one degree. In addition, the comet's northerly motion peaked at +64° on May 15, and it then began a very slight southerly motion.
  • Starting out near magnitude 7.2 at the beginning of June, the comet faded to 12 by mid-August. The tail length was still a degree or so in early June, but had decreased to 4 arc minutes by the end of August. The nucleus was slightly fainter than 11 early in June and was last visually detected on June 20 by Beyer when it had dropped to magnitude 12.7. Photographically, the nucleus was detected at magnitude 14 by Elizabeth Roemer (U. S. Naval Observatory, Flagstaff station) on July 2. The comet's slow southerly motion ended on August 19, when the declination reached +57°.
  • During the last half of September, the comet's total and nuclear magnitudes were estimated as 13 and 18, respectively, while the tail was under two arc minutes. On November 30 Roemer obtained two 60-minute exposures of the comet with the 40-inch f/6.8 Ritchey Chrétien reflector and noted a strongly condensed nucleus of magnitude 18.8 situated within a faint, circular coma 0.2 arc minute across.
  • At the beginning of 1958, magnitude estimates were between 18.5 and 19. The diffuse coma was estimated as 8 arc seconds across, and there was no longer any trace of a tail. The comet reached its most northerly declination of +89.5° on February 12. A 70-minute exposure was obtained by Roemer on March 10. She commented that in poor seeing the "suspected comet image [was] very weak."
  • The comet was last detected on April 11.20 and April 11.27, when Roemer obtained 90- and 85-minute exposures, respectively, with the 40-inch reflector. At that time it was situated 5.51 AU from Earth and 5.36 AU from the sun. Roemer said the "Fairly well-condensed but weak images" were about magnitude 21.0.
  • cometography.com