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C/1921 H1 (Dubiago)


A. D. Dubiago (University Observatory, Kazan, Russia) discovered this comet with the 24-cm refractor on 1921 April 24.78. He estimated the magnitude as 10.5 and noted it was a difficult object to see in the moonlight. Confirmation came on April 25.81, when A. N. Lexin (University Observatory) observed it with the 24-cm refractor.

Historical Highlights

  • At the time of discovery, the comet was approaching both the sun and Earth. The comet attained its most northerly declination of +45° on April 27. Dubiago saw the comet again on the 29th and noted a condensation. K. D. Pokrovskii (Pulkovo Observatory, St. Petersburg, Russia) gave the magnitude as 11 on April 29 and 30. He observed using the 38-cm refractor said the coma was 40 arc seconds across, but exhibited no nucleus on the 30th. On May 1, Pokrovskii said the comet was brighter than on previous nights and gave the magnitude as 10. On the 7th, Pokrovskii said the comet appeared very faint in the 38-cm refractor. On the 9th, Pokrovskii said the comet appeared so faint in the bright northwestern sky that it was impossible to measure its position. On the 14th, R. R. E. Schorr (Hamburg Observatory, Bergedorf, Germany) said the magnitude was 11.5, while the coma was 3 arc minutes across. He added that there was no nucleus. On the 27th, W. Reid (Cape Town, South Africa) observed the comet with a refractor and estimated the magnitude as 11. He wrote, "It is a faint, hazy, nebulous patch, small and fairly round, slightly condensed towards the centre; a very small nucleus can also be glimpsed." Dubiago said the comet was extremely weak in the 24-cm refractor on the 28th and was seen with great difficulty. That same night, J. van der Bilt observed with the 25-cm refractor and described the comet as very faint, with no nucleus. On the 29th, Dubiago said the comet was very difficult to observe. On the 30th, C. Hoffmeister (Sonneberg, Germany) estimated the magnitude as 11 and described the comet as a round nebulosity, with a weak condensation. G. Struve (Berlin-Babelsberg Observatory, Germany) said the comet exhibited no condensation or nucleus in the 65-cm refractor. On May 31, Struve said the comet could only be seen with averted vision while using the 65-cm refractor. As June began, the comet was moving away from both the sun and Earth. On June 2, Struve said seeing was bad and the comet was a difficult object. On the 3rd, Hoffmeister described the comet as weak. On June 7, Struve described the comet as a very faint, diffuse nebulosity.
  • The comet was last detected on July 7.17, when G. van Biesbroeck (Yerkes Observatory, Wisconsin, USA) estimated the magnitude as 13.5. He described the comet as round, 40 arc seconds across, with a faint condensation.
  • The first parabolic orbit was calculated by N. I. Idelson, who took positions from April 29, 30, and May 1, and gave the perihelion date as 1921 May 8.11. Additional calculations were published during the next few weeks by C. W. L. M. Ebell and A. C. D. Crommelin, and the perihelion date was established as May 5.7. Orbits using positions spanning the period of April 24 to June 11 have been calculated by Dubiago (1924), H. Hirose (1936), I. Muraveva (1978), and B. G. Marsden (1979). The perihelion date was given as May 5.62 by Dubiago, May 5.33 by Muraveva, and May 5.35 by Hirose and Marsden. The period was calculated as 79.50 years by Dubiago, 67.0 years by Hirose, 61.0 years by Muraveva, and 62.4 years by Marsden.
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