C / 1947 X1 (southern comet)

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C / 1947 X1 (southern comet) [i]
Properties of the orbit ( animation )
Epoch:  December 1st, 1947 ( JD 2,432,520.5)
Orbit type long-period
Numerical eccentricity 0.99955
Perihelion 0.110 AU
Aphelion 486.8 AU
Major semi-axis 243.4 AU
Sidereal period ~ 3800 a
Inclination of the orbit plane 138.5 °
Perihelion December 2, 1947
Orbital velocity in the perihelion 127.0 km / s
history
Explorer
Date of discovery December 7, 1947
Older name 1947 XII, 1947n
Source: Unless otherwise stated, the data comes from JPL Small-Body Database Browser . Please also note the note on comet articles .

C / 1947 X1 ( southern comet ) is a comet which in 1947 could only be seen with the naked eye during the day in the southern hemisphere . Some consider it one of the " great comets ".

Discovery and observation

On December 3, 1947, the comet had passed the Sun at a distance of less than 6 ° and shortly afterwards appeared quite surprising for observers in the southern hemisphere with already high brightness and a short distance from the Sun at dusk . The first, however, unconfirmed sighting reports from South Africa were already available on the evening of December 7th, when the comet was only 14 ° east of the sun. On December 8th, the comet was seen in Australia even in the daytime sky . Harold S. Pallot, an astronomy teacher, was informed by two teenagers an hour before sunset about a conspicuous bright object in the western sky and, according to his own observation, described it as being much brighter than Venus at the same time and despite the brilliant sunshine as "bright and shining from one end to the other ”. Pallot described the comet's tail as 30 ° long and 25 ° wide and estimated the comet's brightness to be -5 mag.

On December 8th throughout the evening in South Africa, the Royal Observatory at the Cape of Good Hope and the Bloemfontein Observatory received non-stop phone calls from across the country and countless observers reported the sighting of the bright comet. At this point in time, John Stefanos Paraskevopoulos reported a tail over 25 °. On December 9, the comet was also observed by a ship off New Zealand , Australia and South Africa and judged by observers to be brighter than January's Great Comet of 1910 and Halley's Comet when it appeared in 1911.

On December 10th, the comet's brightness was estimated to be 2 mag by an astronomer in Cordoba, Argentina . On this day it was also discovered for the first time that the comet had two nuclei that were about 6 arc seconds apart. The length of the tail was given as 30 °. Shortly thereafter, the comet reached its greatest southern declination and then began to rapidly decrease in brightness. In the middle of the month it was 4 mag and the tail length was only 1–2 °. The comet's two nuclei were observed as they slowly diverged from each other. By Christmas, the comet's brightness had fallen below the level of visibility with the naked eye.

At the beginning of January 1948 a brightness of about 8–9 mag could be determined. The two core fragments had now drifted apart by up to a distance of about 20 arc seconds. The last observation was on January 20, 1948.

The comet reached a maximum brightness of -1 mag.

Scientific evaluation

Numerous spectrograms of the comet were recorded from mid-December 1947 to early January 1948. The spectral lines could be assigned to numerous chemical compounds.

Zdenek Sekanina analyzed the motion of the comet's two nuclei and described in a scientific paper from 1978 that the nucleus of comet C / 1947 X1 probably broke in two on November 30, about two days before its closest approach to the sun was. After that, the fragments only moved away from each other at a low speed of 1–2 m / s. The decay was not caused by tidal forces ( nontidal splitting ). The dust releases associated with this decay process were probably responsible for the extreme outbreak of brightness of the comet as it passed the sun.

Orbit

For comet fragment A, a limited precise elongated elliptical orbit could be determined from 44 observation data over a period of 41 days , which is inclined by around 139 ° to the ecliptic . The comet thus runs in the opposite direction (retrograde) like the planets through its orbit. The track elements of fragment A are given in the info box as an example. The fragment B initially only moved relatively slowly away from the fragment A and elements of an orbit could also be determined from 29 observation data over a period of 38 days.

At the point of the orbit closest to the sun ( perihelion ), which the comet fragments traversed on December 2, 1947, they were about 16.5 million km from the sun, well within the orbit of Mercury . On November 15, the comet had passed Venus at a distance of around 68.0 million km and on November 30, it had passed Mercury at a distance of 39.3 million km. After passing through the perihelion, the fragments reached the closest approach to Earth on December 7, at around 0.85 AU / 127.1 million km . On December 29, there was a second close passage of Venus at a distance of about 40.9 million km.

Since only orbital elements for the two comet fragments A and B were determined, no definitive statements can be made about the orbit of the comet before its decay, especially since non-gravitational effects may have played a role during the decay and when it passed close to the sun . From the orbit of the lighter and probably larger fragment A, it can be assumed that the comet was already moving on an extremely elongated elliptical orbit around the sun before it passed the inner solar system in 1947. Its orbital period was probably a few thousand years. Due to the gravitational pull of the planets, in particular due to two relatively close passages of Jupiter on October 6, 1947 and October 14, 1949 at a distance of about 4 4 AU each, the orbital eccentricity of fragment A was about 0.99941 and the semi-major axis about 190 AU reduced, so that its orbital period was shortened to about 2,650 years. For fragment B, for which the second rendezvous with Jupiter took place almost nine hours later and at a distance of around 850,000 km more than for fragment A, the orbital eccentricity was reduced to around 0.99949 and the semi-major axis to around 223 AU, so that its orbital period is now around 3300 years.

See also

Individual evidence

  1. ^ John E. Bortle: International Comet Quarterly - The Bright-Comet Chronicles. Retrieved September 25, 2015 .
  2. ^ DAJ Seargent: The Greatest Comets in History: Broom Stars and Celestial Scimitars. Springer, New York, 2009, ISBN 978-0-387-09512-7 , pp. 236-237.
  3. ^ A b Gary W. Kronk : Cometography - A Catalog of Comets. Volume 4: 1933-1959. Cambridge University Press, Cambridge 2009, ISBN 978-0-521-58507-1 , pp. 276-282.
  4. ^ P. Moore, R. Rees: Patrick Moore's Data Book of Astronomy. Cambridge University Press, Cambridge 2011, ISBN 978-0-521-89935-2 , p. 271.
  5. ^ Z. Sekanina: Relative motions of fragments of the split comets. II - Separation velocities and differential decelerations for extensively observed comets. In: Icarus. Volume 33, 1978, pp. 173-185 doi: 10.1016 / 0019-1035 (78) 90031-3 .
  6. ^ Z. Sekanina: The problem of split comets revisited. In: Astronomy and Astrophysics. Volume 318, 1997, pp. L5-L8, bibcode : 1997A & A ... 318L ... 5S .
  7. ↑ H. Boehnhardt: Split Comets. In: MC Festou, HU Keller, HA Weaver (eds.): Comets II. University of Arizona Press, Tucson, 2004, pp. 301-316 ( lpi.usra.edu PDF; 1.95 MB).
  8. ↑ NASA JPL Small-Body Database Browser: C / 1947 X1-A. Retrieved September 25, 2015 .
  9. ↑ NASA JPL Small-Body Database Browser: C / 1947 X1-B. Retrieved September 25, 2015 .
  10. ↑ SOLEX 11.0 A. Vitagliano. Archived from the original on September 18, 2015 ; accessed on May 2, 2014 .