C / 1974 C1 (Bradfield)

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C / 1974 C1 (Bradfield) [i]
Properties of the orbit ( animation )
Epoch:  March 14th 1974 ( JD 2,442,120.5)
Orbit type long-period
Numerical eccentricity 0.99970
Perihelion 0.503 AU
Aphelion 3321 AE
Major semi-axis 1661 AE
Sidereal period ~ 67,700 a
Inclination of the orbit plane 61.3 °
Perihelion March 18, 1974
Orbital velocity in the perihelion 59.4 km / s
history
Explorer WA Bradfield
Date of discovery February 12, 1974
Older name 1974 III, 1974b
Source: Unless otherwise stated, the data comes from JPL Small-Body Database Browser . Please also note the note on comet articles .

C / 1974 C1 (Bradfield) is a comet that could be seen with the naked eye in 1974 . The comet turned out to be just as spectacular and easily observable as C / 1973 E1 (Kohoutek) the year before, but since it was discovered just a month before it approached the Sun, it received far less attention from both professional and journalistic backgrounds .

discovery

The comet was on the evening of February 12, 1974 (local time) by William A. Bradfield in Australia with a mm 150 - f / 5.5 - Refractor discovered. It was his second comet discovery, 13 months after his first. During this period he had searched for comets for a total of 306 hours. Bradfield estimated the comet's brightness to be around 9 mag and did not repeat his observation until the following day before making the discovery public.

The comet could then also be observed by many observers in Australia, New Zealand and Chile by the end of the month . In March its brightness increased significantly and reached about 4 mag towards the end of the month with a tail length of over 4 ° visually and 11 ° photographically. From this time on it moved northward in the sky and was then also visible from the northern hemisphere . In April, however, its brightness quickly decreased again and at the end of the month was only 8 mag. On May 14th, it passed the celestial north pole at a distance of only about ⅔ ° . By the beginning of June the brightness had dropped below 10 mag. The last observation was on November 18.

The comet reached a maximum brightness of 3.9 mag.

Scientific evaluation

Spectroscopic examinations of the comet's dust tail in the infrared wavelength range showed the emission lines of silicates , which indicated the presence of grains <5 µm in the coma and tail of the comet. The silicate lines were detectable at a distance of the comet from the sun of 0.5 AU, but disappeared when the comet moved more than 0.6 AU from the sun, combined with a simultaneous abrupt decrease in brightness, which indicates a sudden end to dust production suggests.

After Comet Kohoutek in the previous year, Comet Bradfield was only the second comet in which, in addition to the comet-typical emission lines of C 2 , NH 2 and CN, the presence of ionized water (H 2 O + ) in the plasma tail could be detected spectroscopically. For the first time, the presence of the 1.35 cm line of the water molecule could also be detected with a radio telescope . This microwave radiation is possibly caused by a maser effect around the comet's nucleus.

For the comet in 1975 Brian Marsden was able to determine orbital elements of two slightly different elliptical orbits from 159 observation data over a period of 277 days . In a first calculation he only took into account the gravitational influences from all planets . In the second calculation, he also took non-gravitational effects into account . The second calculation showed a slightly better agreement between the calculated and the observed position data. These track elements are indicated in the info box. Marsden also derived values ​​for the comet's original orbit before the passage of the inner solar system and for its future orbit from the data sets .

In a more recent study in 2006, Królikowska determined new values ​​for the original orbit of the comet before the passage of the inner solar system and for its future orbit from 198 observation data over a period of 277 days, once again only taking into account gravitational effects and once taking into account non-gravitational effects. For the purely gravitational calculation, this investigation showed very similar results to those of Marsden. When non-gravitational effects are taken into account, however, in contrast to Marsden's results, the values ​​for the original orbit of the comet were significantly larger for the semi-major axis or orbital period .

Orbit

For the comet, an elliptical orbit with limited accuracy could be determined from 159 observation data over a period of 277 days, which is inclined by around 61 ° to the ecliptic . At the point of the orbit closest to the sun ( perihelion ), which the comet last traversed on March 18, 1974, it was located at a distance of about 75.3 million km from the sun in the area just outside the orbit of the sun-closest planet Mercury . On March 23, the closest approach took place both to Venus with about 120.2 million km and to Mars with about 180.0 million km. On March 30, it came close to Earth to within 0.67 AU / 100.3 million km.

The comet moves in an extremely elongated elliptical orbit around the sun. The following information is based on the investigation by Królikowska taking into account non-gravitational effects. According to this, some time before the passage of the inner solar system in 1974, its orbit had an eccentricity of about 0.99972 and a semi-major axis of about 1775 AU, so that its orbit period was about 74,700 years. Due to the gravitational pull of the planets, especially due to the relatively close passages of Jupiter on July 2, 1973 in only about 2½ AU and on June 28, 1974 in about 5½ AU, its orbital eccentricity was about 0.99960 and its semi-major axis to reduced by about 1275 AU, so that its orbital period was shortened to about 45,400 years.

See also

Web links

Individual evidence

  1. ^ BG Marsden, E. Roemer: Comets in 1974. In: Quarterly Journal of the Royal Astronomical Society. Vol. 19, 1978, pp. 38-58 ( bibcode : 1978QJRAS..19 ... 38M ).
  2. ^ Astronomical Society of South Australia: Comets Discovered from South Australia. Accessed December 12, 2015 .
  3. ^ GW Kronk, M. Meyer: Cometography - A Catalog of Comets, Volume 5, 1960-1982 . Cambridge University Press, Cambridge 2010, ISBN 978-0-521-87226-3 , pp. 416-421.
  4. ↑ International Comet Quarterly - Brightest comets seen since 1935. Retrieved on December 14, 2015 .
  5. ↑ EP Ney: Optical and infrared observations of bright comets in the range 0.5 µm to 20 µm. In: LL Wilkening, MS Matthews (Ed.): Comets. University of Arizona Press, Tucson 1982, ISBN 0-8165-0769-4 , pp. 323-340.
  6. ↑ P. Wehinger, S. Wyckoff: H 2 O + in Spectra of Comet Bradfield (1974b). In: The Astrophysical Journal. Vol. 192, 1974, pp. L41-L42 ( bibcode : 1974ApJ ... 192L..41W ).
  7. ^ WM Jackson, T. Clark, B. Donn: Radio Detection of H 2 O in Comet Bradfield (1974b). In: The Study of Comets. Part 1. The Proceedings of IAU Colloquium No. 25, 1974. NASA Scientific and Technical Information Office, Washington DC 1976, pp. 272-280 ( PDF; 29.9 MB ).
  8. ↑ VS Strel'nitskii: The water maser emission from Comet Bradfield 1974 III. In: Soviet Astronomy Letters. Vol. 9, 1983, pp. 99-101 ( bibcode : 1983SvAL .... 9 ... 99S ).
  9. ^ IAU Central Bureau for Astronomical Telegrams - IAUC 2762: 1973 IX; 1974b. Retrieved December 16, 2015 .
  10. ^ BG Marsden, Z. Sekanina, E. Everhart: New Osculating Orbits for 110 Comets and Analysis of Original Orbits for 200 Comets. In: The Astronomical Journal. Vol. 83, no. 1, 1978, pp. 64-71 doi: 10.1086 / 112177 ( bibcode : 1978AJ ..... 83 ... 64M ).
  11. ↑ a b M. Królikowska: The Oort spike modification due to non-gravitational effects. Submitted for publication in: Astronomy and Astrophysics. 2006, pp. 64-71 ( arxiv : astro-ph / 0609441 ).
  12. ↑ NASA JPL Small-Body Database Browser: C / 1974 C1 (Bradfield). Accessed December 12, 2015 .
  13. ↑ A. Vitagliano: SOLEX 11.0. Archived from the original on September 18, 2015 ; accessed on May 2, 2014 .