Copyright © 2007 by Mike F. Holloway (Van Buren, Arkansas, USA)
This image was obtained by M. F. Holloway on 2007 April 12.
The comet was first discovered on 1786 January 17.8, by Pierre Méchain (Paris, France) while searching for comets in the Aquarius region. Mechain said the comet appeared fairly bright when viewed through a telescope and exhibited a faint, narrow tail. No observations were possible on the 18th, but Méchain and Charles Messier were able to confirm the comet on the 19th. Unfortunately, the comet's elongation from the sun was rapidly decreasing and no observations were made after the 19th. Subsequently, no orbit was computed. The comet passed closest to Earth (0.62 AU) on January 23.
The comet's second discovery was made by Caroline Herschel (Slough, England) during a routine sweep for comets on 1795 November 7.8. It was quickly confirmed by her brother William Herschel, who noted it could be seen with the naked eye. The comet was closest to Earth (0.26 AU) on November 9, and observations continued as the comet's elongation from the sun decreased. The comet was last detected on November 29.
The comet's third discovery was made by Jean Louis Pons (Marseille, France) on 1805 October 20, with independent discoveries being made by Johann Sigismund Huth (Frankfurt an der Oder, Germany) on the 21st and Alexis Bouvard on the 22nd. On the 23rd Huth said the comet was visible to the naked eye and was similar in size and brightness to the Andromeda Galaxy (M31). The comet was last detected on November 20. Later calculations revealed the comet had passed closest to Earth (0.44 AU) on October 16.
The comet's fourth discovery was made by Pons (Marseille, France) on 1818 November 27.9. He described it as very faint. The comet passed closest to Earth (0.60 AU) on 1819 January 17.
J. F. Encke would ultimately be the first person to recognize that comets discovered in 1786, 1795, 1805, and 1818 were the same comet. Encke first began to notice this relationship while investigating the orbit of Pons' comet of 1818-19. He published a parabolic orbit in the February 1819 issue of the Correspondance astronomique. He took positions obtained on 1818 December 22, January 1, and 6, and determined a perihelion date of 1819 January 25.40. The article added that the orbit "resembles a little that of the first comet of 1805; perhaps later calculations will teach us something on their identity." Encke published another article in the same issue of the Correspondance astronomique which gave the first elliptical orbit. He took positions from November 30 to January 12 and determined a perihelion date of January 27.60 and a period of 4.15 years. He compared his orbit for the 1819 comet, with the parabolic orbit calculated by Bessel for the 1805 comet and said the differences between the two were within the limits of what planetary perturbations can produce. In the March 1819 issue of the Correspondance astronomique, Encke showed the results of his calculations of an elliptical orbit for the 1805 comet. The comparison between the orbits of the comets of 1805 and 1819 now showed very little difference, and Encke was sure the two were identical. He continued working on the problem and, in May of 1819, Encke published details of his attempts to link the comets of 1805 and 1819 to a comet observed in 1795. During June of 1819, Encke had successfully linked this comet to one seen on only two nights in 1786. It was this laborious investigation that led to the comet being named "Encke".
Apparition of 1822 (first predicted return): During 1819, Encke suggested the comet would likely return during May of 1822. About a year later, he took the positions from the 1818-19 apparition and determined a perihelion date of 1822 May 24.97. There was an ephemeris for the period of 1822 February 25 to July 27. One of the earliest documented searches was made by J. E. Bode (Berlin, Germany) on the evening of 1822 February 15. Using a 3.5-foot focal length refractor he swept the area the comet was predicted to be located, which was the region south of Omega Piscium. No trace of the comet was found. Calculations now reveal the comet was in the predicted region, but was then too faint for recovery. It was moving quite slowly because of its distance from the Earth and sun, and that area of the sky was carried into twilight during March and then daylight by the end of April. It passed 10° from the sun on April 24, and then slowly moved away. C. K. L. Rümker (Paramatta, New South Wales) recovered this comet with the aid of Encke's ephemeris on 1822 June 2.33. The comet was then situated very low in the evening sky. Rümker confirmed the recovery and therefore the identity with the expected comet on June 3.33. The comet was about a half day earlier than Encke's prediction. Physical descriptions were few during this apparition, with the bulk coming from W. Robertson and C. Drinkwater (H.M.S. Creole, in harbor of Rio de Janeiro, Brazil), who managed to observe the comet after sunset for nearly two weeks during June. They described the comet as "like a faint nebula of a round form" on June 7. They said it appeared faint in a telescope on the 12th, while on the 13th they remarked that the comet had not increased in brightness since it was seen on the 7th. On June 17, Robertson and Drinkwater noted the comet had "the same nebulous, orbicular appearance as when first seen." They again described it as "very faint" in a telescope on the 18th. Further attempts to see the comet on the 19th and 22nd, proved fruitless, first because of hazy skies, and then because of moonlight. Rümker measured the comet's position for the final time on June 23.37. He noted its faintness and the fact that increasing moonlight would hamper further observations. The last apparent observation came on June 29.4, when Rümker detected a faint glow near the expected position, but no precise measurements were possible. Rümker's searches in early July revealed no trace of the comet.
Magnitude estimates were not made until the late 19th century, but astronomers have attempted to determine the maximum brightness of this comet at each of its returns. It seems apparent that the comet has faded since 1786. The greatest recorded brightness was about 3.5 in 1829, while a value of 4.0 was indicated in 1805. The comet has not been observed as brighter than magnitude 5.0 during the 20th century. A magnitude of 5.0 was last registered in 1964.
The comet's longest recorded tail length was 3 degrees in 1805, while it reached 2 degrees in 1871 and 1961.
Although the orbit of this comet appears to have been stable for several thousand years, it is puzzling to astronomers that ancient or medieval comets have not been linked to comet Encke. It is especially perplexing considering the comet was seen with the naked eye during several returns during the 19th century.
The comet's maximum brightness was estimated as near 6 during 1997 and 7 during 2000. The comet's 60th observed apparition came in 2003. It was well observed and extensively photographed as it moved through the evening sky and attained a maximum magnitude near 6.5.
Close approaches to planets: The comet experienced one close approach to Mercury, eleven close approaches to Earth, and two close approaches to Jupiter during the 20th century. It will make three close approaches to Earth and one close approach to Jupiter during the first three decades of the 21st century. None of the close approaches to Jupiter produce notable changes to the comet's orbit, so details of alterations in the perihelion distance and period are excluded. (From the orbital work of Kazuo Kinoshita)
- 0.91 AU from Jupiter on 1903 May 31
- 0.48 AU from Earth on 1904 December 12
- 0.06 AU from Mercury on 1905 January 11
- 0.32 AU from Earth on 1908 June 16
- 0.29 AU from Earth on 1914 October 27
- 0.31 AU from Earth on 1931 July 13
- 0.27 AU from Earth on 1937 November 15
- 0.42 AU from Earth on 1947 October 20
- 0.90 AU from Jupiter on 1962 September 28
- 0.33 AU from Earth on 1964 July 13
- 0.42 AU from Earth on 1970 December 1
- 0.36 AU from Earth on 1974 June 14
- 0.28 AU from Earth on 1980 October 28
- 0.19 AU from Earth on 1997 July 5
- 0.26 AU from Earth on 2003 November 17
- 0.48 AU from Earth on 2013 October 17
- 0.91 AU from Jupiter on 2022 January 27
- 0.27 AU from Earth on 2030 July 11
Copyright © 1993 by James V. Scotti
This image was taken by James V. Scotti (Spacewatch) on 1993 October 24. He used a 0.9-m Spacewatch telescope. The comet is nearly stellar, with only a faint trace of coma and a hint of tail extending towards the upper right.
Copyright © 1994 by James V. Scotti
This image was taken by James V. Scotti (Spacewatch) on 1994 January 5. He used a 0.9-m Spacewatch telescope. The nuclear region is still visible, but the comet now displays a larger coma and a more prominent tail that extends upwards with a slight tilt to the right.
Copyright © 1994 by Gerald Rhemann (Austria)
This image was obtained on 1994 January 9.78 UT with the 171/200/257mm Schmidt camera. Exposure time was 5 minutes and the photographic emulsion was hypered Technical Pan 2415. The comet's total magnitude was then about 8.5. (The image has been cropped by the webmaster to save space.)
Copyright © 1997 by Gordon Garradd (Australia)
This photo of periodic comet Encke was obtained by G. Garradd on 1997 June 5. It was a 100-second exposure obtained with a 25-cm Newtonian and a CCD camera. The comet was then slightly more than two degrees above the horizon. A thin gas tail can be seen. The field of view of the image measures 8 arcmin high and 19 arcmin wide. The coloring does not represent the comet's true color, but was used to enhance some of the faint features.
Copyright © 2003 by R. Ligustri (Talmassons, Italy)
This image was obtained on 2003 September 20.94 UT with the 350/1750 reflector and an SBIG ST9E CCD camera. Three 120-second exposures were combined. The image covers a field measuring 16' by 16'. North is toward the top, while east is to the left.
Copyright © 2003 by Giovanni Sostero (Remanzacco Observatory, Italy)
This image was obtained on 2003 October 15.97 UT with the 0.45-m f/4.5 Newtonian reflector and a CCD camera. Six 30-second unfiltered exposures were combined. The false coloring of the image highlights the diffuse nature of the tail, which is actually a fan of material extending sunward.
Copyright © 2003 by Gerald Rhemann and Michael Jäger (Austria)
This color image was obtained by G. Rhemann and M. Jäger on 2003 November 12. It is composed of three 30-second exposures obtained with a 250/450 Schmidt camera and a Starlight SXV-H9 CCD camera.