Copyright © 2001 by Giovanni Sostero (Remanzacco Observatory, Italy)
This image was obtained by G. Sostero on 2001 October 18.10. It is a combination of 6 60-second exposures obtained with a 0.30-m f/2.8 Baker-Schmidt camera and a Hi-Sis 24 CCD camera.
During the course of a routine photographic survey of minor planets with the 40-cm Bruce photographic telescope, Karl Reinmuth (Königstuhl Observatory, Heidelberg, Germany) discovered this comet on 1947 September 10.91. He estimated the magnitude as 13.
The comet was quickly found to be a periodic comet, with Leland E. Cunningham (Student's Observatory, Berkeley, California, USA) taking positions measured through September 20 and calculating an elliptical orbit with a perihelion date of 1947 October 3.37 and an orbital period of 7.12 years. Revisions by Cunningham and others during the next couple of months ultimately revealed a perihelion date of 1947 August 19 and a period of 6.59 years. For a brief time, this comet was thought to possibly be a return of the lost periodic comet Tuttle-Giacobini (later Tuttle-Giacobini-Kresak), but Eugene Karl Rabe proved this an impossibility during February of 1948.
Apparition of 1947: The comet was nearly one month passed perihelion when discovered and was less than one day from its closest approach to Earth. Although it should have been slowly fading in the weeks that followed, the comet changed little in brightness during the first month of visibility and did not actually start fading until after mid-October of 1947. The comet was slightly brighter than magnitude 14 at the beginning of November and was near 15 as December began. The comet followed until 1948 February 1, when Hamilton Moore Jeffers and B. J. Mattson (Lick Observatory, California, USA) photographed the comet with the 36-inch f/5.8 Crossley reflector. They determined the magnitude as 17.7.
Rabe worked on the definitive orbit for this comet's 1947 apparition during 1953. From this he predicted the comet would next pass perihelion on 1954 March 27. George van Biesbroeck recovered this comet on a 20-minute exposure obtained with the 82-inch reflector at McDonald Observatory on July 5.20. The magnitude was estimated as 19 and the diffuse round coma was about 3" across. The comet never became brighter than magnitude 17.5 during this apparition.
As it turns out, the comet's large perihelion distance of about 1.9 AU typically keeps it a faint object at each return. The reason for the somewhat bright appearance in 1947 was because it was experiencing one of its closest approaches to Earth of 0.89 AU. On the other hand, this same large perihelion distance, when coupled with a moderate eccentricity, enables the comet to be followed for a long period of time at each apparition. This has enabled the comet to be seen at every return since its discovery, including those of 1954 and 1969, when the comet reached perihelion at the same time it was in conjunction with the sun.
The comet last passed closest to the sun on 2001 February 19. Future returns will be somewhat more unfavorable as the comet will pass 0.74 AU from Jupiter during July of 2003, which increases the perihelion distance. Interestingly, the comet is entering a cycle of increasingly closer approaches to Jupiter which will result in the orbit undergoing some significant changes. Jupiter approaches of 0.52 AU in 2039 and 0.44 AU in 2063 will ultimately increase the perihelion distance to 2.66 AU and the period to 8.09 years.
Close approaches to planets: This comet made two close approaches to Earth during the 20th century. It makes two close approach to Jupiter during the first half of the 21st century. (From the orbital work of Kazuo Kinoshita)
- 0.89 AU from Earth on 1947 September 11
- 0.96 AU from Earth on 1967 September 12
- 0.74 AU from Jupiter on 2003 July 16
- increased perihelion distance from 1.89 AU to 2.11 AU
- increased orbital period from 6.63 to 7.07 years
- 0.52 AU from Jupiter on 2039 February 11
- increased perihelion distance from 2.10 AU to 2.44 AU
- increased orbital period from 7.06 to 7.78 years