D / 1770 L1 (Lexell)

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D / 1770 L1 (Lexell) [i]
Properties of the orbit ( animation )
Period:  August 14, 1770 ( JD 2,367,764.5)
Orbit type short-term
Numerical eccentricity 0.786
Perihelion 0.674 AU
Aphelion 5.63 AU
Major semi-axis 3.15 AU
Sidereal period 5.6 a
Inclination of the orbit plane 1.6 °
Perihelion August 14, 1770
Orbital velocity in the perihelion 48.5 km / s
history
Explorer Charles Messier
Date of discovery June 14, 1770
Older name 1770 I.
Source: Unless otherwise stated, the data comes from JPL Small-Body Database Browser . Please also note the note on comet articles .

D / 1770 L1 (Lexell) was a comet that could be seen with the naked eye in 1770 . He was the one of all comets in historical times, which the earth came the next.

Discovery and observation

The comet was discovered on June 14, 1770 by Charles Messier , who was just observing Jupiter , when he discovered an unfamiliar nebula in the constellation Sagittarius . Its brightness was probably around 5 mag.

At the time of its discovery, the comet was approaching the sun and earth . Its size increased rapidly and Messier was able to observe it with the naked eye for the first time on June 20th; on June 24th it had already reached a brightness of 2 mag. The comet was first observed in China and North America on June 26th, and also in England a day later . The comet had no tail , but its coma was ½ ° in diameter .

Towards the end of June the comet was moving at great speed across the sky, and when it passed Earth on July 1st at a distance of only 2 million km, its coma appeared almost 2½ degrees, five times the size of the full moon. The comet moved 42 ° across the sky in 24 hours and reached its greatest northerly declination at + 81 ° on July 2nd . A few days later it could no longer be observed as it approached the sun more and more and disappeared into the bright twilight .

While the comet could not be observed, a preliminary orbit was calculated by Alexandre Guy Pingré , so that Messier began again to search for the comet at dawn on July 19. Due to bad weather, he could not find him until August 3rd. The observations could then be continued during August and September. On August 11th the brightness had dropped to 4 to 5 mag, and on August 20th Messier was able to observe a very faint tail for the first time. Soon afterwards it was no longer possible to observe with the naked eye and by the end of August the brightness had dropped to 5 to 6 mag.

From September the comet was only observed by Messier. On October 2nd, Messier described him as "almost invisible" and on October 3rd as "extremely weak and very difficult to observe". On this date the comet was seen for the last time.

The comet reached a brightness of 2 mag.

Scientific evaluation

For this comet a problem arose from the beginning in the determination of an orbit that was to be brought into harmony with the observed positions in the sky. As was common at the time, an attempt was first made to determine a parabolic path. This happened for the first time during the ongoing observation of the comet by Alexandre Guy Pingré, which meant that the comet could be found again quickly after passing the sun. Soon afterwards, however, Pingré himself discovered that the further observation data of the comet could no longer be reconciled with parabolic orbits and instead wanted to calculate orbit elements of an elliptical orbit. However, this was already in good agreement with the observation data by the Swedish astronomer Anders Johan Lexell in Saint Petersburg , who had determined the comet's orbital period of 5.58 years. The comet thus had the shortest known orbital time.

But this raised a new problem: It was not just Pingré that asked why the comet had never been observed before in such a short orbit. Lexell was also able to give an answer to this: About 3½ years before its discovery, the comet passed very close to Jupiter in March 1767 , which could have brought it to this new orbit with a short orbital period for the first time, which then became his Discovery led in 1770. During the subsequent passage of the perihelion in March 1776, it was standing behind the sun when viewed from the earth and could therefore not be observed.

But why did you never see him again afterwards? For Messier, this question was a reason to doubt the results of Lexell's research. Lexell showed, however, that the orbital time of the comet was in a 2: 1 orbital resonance with that of Jupiter: The comet made exactly two orbits around the sun while Jupiter made one orbit. As a result, there was another extremely close passage to Jupiter in 1779, possibly even closer than the one in 1767, which again may have caused a major change in its orbit. Lexell's work to elucidate the comet's unusual orbit is widely recognized today and earned him the honor of naming the comet after him and not after Messier, who discovered it.

In the middle of the 19th century , the orbit of Comet Lexell was examined again very carefully by Urbain Le Verrier . He also took into account the gravitational influence of the earth when the comet passed close by. He came to the conclusion that the duration of the observation and the accuracy of the data were not sufficient to determine the orbit with the accuracy required to allow definitive statements about the fate of the comet. Only the following general statements can be made:

  • When it passed close to Jupiter in 1779, the comet did not become a satellite of the giant planet and there was no collision.
  • It cannot be said with certainty whether the comet passed Jupiter inside or outside Jupiter's orbit.
  • Depending on the exact circumstances when passing Jupiter, which may have occurred at a distance of between 200,000 and 10 million km, the comet was either put on another short-period orbit (unlikely, since it was not seen again), or on a long-period one Orbit of up to several hundred years of orbit (most likely). In a less likely case, the comet could even have been catapulted out of the solar system on a hyperbolic orbit.

Elena I. Kazimirchak-Polonskaya and SD Shaporev also came to comparable results in 1976 when they investigated the development of the orbit using modern methods.

Although it didn't dwell in this category long, Comet Lexell was the first known comet from the Jupiter family . His tissue edge parameter was 2.6. In addition, it was the first identified near-earth object (NEO).

Until the beginning of the 19th century, ideas about the mass of comets diverged widely, and Immanuel Kant assumed values ​​that were comparable to those of the largest planets . In 1805, Pierre-Simon Laplace was able to deduce an upper limit for the comet's mass by evaluating the close encounter between the earth and comet Lexell, which had not caused any noticeable disturbance in the motion of the earth. He found that the comet's mass could not be greater than 1/5000 the mass of the earth. This provided proof that the coma and tail of the comet, despite their size, are of extremely low density .

Orbit

The following information is derived from the second set of orbital elements determined by Urbain Le Verrier in 1848 , which is based on approximately 130 observations over a period of 110 days. At the point of the orbit closest to the sun ( perihelion ), which the comet passed through on August 14, 1770, it was located at about 100.9 million km from the sun in the area of ​​the orbit of Venus . Already on July 1st it had approached the earth to about 0.015 AU / 2.26 million km, which corresponds to almost 6 times the mean distance from the earth to the moon . This was the closest comet's approach to Earth observed before 2006. On September 1, the comet passed Mars at a distance of 105.4 million km .

At that time the comet had an orbital period of about 5.6 years. After the comet had circled the sun one and a half times, the comet passed extremely close to Jupiter at the end of July 1779 , which affected its orbit so much that it has not been observed from Earth since then. No statement can therefore be made about its current orbit, it is considered lost.

See also

Web links

Individual evidence

  1. a b Historic Comet Close Approaches. Retrieved October 31, 2014 .
  2. ^ GW Kronk: Cometography - A Catalog of Comets, Volume 1. Ancient - 1799 . Cambridge University Press, Cambridge 1999, ISBN 978-0-521-58504-0 , pp. 447-451.
  3. ^ A b c Peter Grego: Blazing a Ghostly Trail: ISON and Great Comets of the Past and Future . Springer, Cham 2013, ISBN 978-3-319-01774-7 , pp. 77-78.
  4. ^ P. Moore, R. Rees: Patrick Moore's Data Book of Astronomy . Cambridge University Press, Cambridge 2011, ISBN 978-0-521-89935-2 , p. 265.
  5. ^ AG Pingré: Cométographie ou Traité historique et théorique des comètes. Tome II, Paris 1784, pp. 85-90.
  6. ^ Jean Meeus: Mathematical Astronomy Morsels III . Willman-Bell, Richmond 2004, ISBN 0-943396-81-6 , pp. 183-185.
  7. Elena I. Kazimirchak-Polonskaya, SD Shaporev: Evolution of orbits of comets Kearns-Kwee (1963 VIII) and Lexell (1770 I) and some regularities of the transformations of the cometary orbits in the sphere of action of Jupiter. In: Soviet Astronomy. Vol. 20, No. 6, 1976, pp. 740-744 ( bibcode : 1976SvA .... 20..740K ).
  8. a b D / 1770 L1 (Lexell) in the Small-Body Database of the Jet Propulsion Laboratory (English).Template: JPL Small-Body Database Browser / Maintenance / Alt
  9. Giovanni B. Valsecchi: 236 years ago… In: Near Earth Objects, our Celestial Neighbors: Opportunity and Risk, Proceedings of IAU Symposium 236. Cambridge University Press, Cambridge 2007, pp. Xvii-xx doi: 10.1017 / S1743921307002980
  10. Julio A. Fernández: Comets - Nature, Dynamics, Origin, and their Cosmogonical Relevance . Springer, Dordrecht 2005, ISBN 978-1-4020-3490-9 , pp. 39-40.
  11. SOLEX 11.0 A. Vitagliano. Archived from the original on September 18, 2015 ; accessed on May 2, 2014 .