Copyright © 2004 by Mihelcic Matej (Vega Observatory, Slovenia)
This image was obtained on 2004 March 18.12, by Mihelcic Matej using a 10-inch f/6.3 reflector and an MX5 CCD camera. It is a 120-second exposure.
Yrjö Väisälä (University of Turku, Finland) discovered this comet on photographs exposed for the study of minor planets. It was first found on 1939 February 8.80, and was given the asteroidal designation of 1939 CB. Shortly thereafter, pre-discovery images were found on plates taken at the same observatory on January 19. Väisälä obtained additional confirmation and identified the object as a comet on plates exposed on March 14.92. At that time he described it as diffuse, without a central condensation or nucleus, and about magnitude 15. From the available positions, Liisi Oterma was able to compute an elliptical orbit which had a period of about 10 years, a perihelion date of 1939 April 26.0, and a perihelion distance of 1.75 AU.
Apparition of 1939: Although many observers indicated the comet's brightness held at 15th magnitude during March and into April, there were several observers who indicated the comet reached magnitude 14 or brighter during late March and early April. From May until the comet was last seen on June 8, observations were obtained only by George van Biesbroeck (Yerkes Observatory, Wisconsin, USA) and Hamilton M. Jeffers (Lick Observatory, California, USA). The former astronomer reported the comet faded from 15 to 15.5 during May and reached 16.5 by June 5. Jeffers photographed the comet on June 8 and gave the magnitude as 17. After all of the observations were in Oterma computed an orbit which indicated the orbital period was 10.58 years.
Apparition of 1949: Oterma's prediction for the 1949 return enabled Antonín Mrkos (Skalnaté Pleso Observatory, Czechoslovakia) to recover this comet on 1949 December 19. He estimated the magnitude as 17, and described the comet as diffuse, without a central condensation. Leland E. Cunningham (Student's Observatory, Berkeley, California, USA) said Mrkos' measured position indicated the comet's perihelion date was 0.84 days later than that predicted by Oterma. The comet was already a month passed perihelion when it was recovered. Subsequently, it steadily faded to magnitude 18 by April 1950 and 19.5 during May.
This comet has been seen at every subsequent return, although it never becomes particularly bright. During the 1960 apparition the comet reached magnitude 14.0 and showed a tail about 1 arc minute long. During 1971 and 1982 the comet reached magnitudes of 20.0 and 19.0, respectively, and never showed a tail. During the 1993 apparition, the comet's maximum magnitude slightly exceeded 14, and the greatest coma diameter was nearly one arc minute.
Apparition of 2004: The comet was observed at a magnitude of 17.5 during the fall of 2003. Professional and amateur astronomers followed the comet using CCD cameras into 2004, as the magnitude steadily increased to about 15 by March 1. Although the comet passed perihelion on 2004 January 22, it continued to approach Earth until late April.
Close approaches to planets: The comet experienced four close approaches to Earth and two close approaches to Jupiter during the 20th century. It makes one close approach to Earth and one close approach to Jupiter during the 21st century.
- 0.77 AU from Earth on 1918 March 18
- 0.89 AU from Earth on 1939 March 1
- 0.98 AU from Earth on 1960 February 22
- 0.41 AU from Jupiter on 1961 December 31
- increased perihelion distance from 1.74 AU to 1.87 AU
- increased orbital period from 10.46 to 11.28 years
- 1.00 AU from Jupiter on 1973 September 22
- decreased perihelion distance from 1.87 AU to 1.80 AU
- decreased orbital period from 11.28 to 10.88 years
- 0.92 AU from Earth on 1993 March 2
- 0.90 AU from Jupiter on 2024 March 26
- increased perihelion distance from 1.820 AU to 1.824 AU
- decreased orbital period from 10.98 to 10.99 years
- 0.88 AU from Earth on 2070 March 24
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