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C/1969 Y1

Comet Bennett on 30 March 1970
Discovery
Discovered by	John Caister Bennett
Discovery date	28 December 1969
Designations
Alternative designations	Comet Bennett, 1969 Y1
Orbital characteristics
Epoch	2440680.5 (April 4, 1970)
Aphelion	282 AU
Perihelion	0.538 AU
Semi-major axis	141 AU
Eccentricity	0.9962
Orbital period	1678 a
Inclination	90.0°
Last perihelion	March 20, 1970
Next perihelion	3600s

Comet Bennett, formally known as C/1969 Y1 (old style 1970 II and 1969i), was one of the two bright comets observed in the 1970s, along with Comet West and is considered a great comet. The name is also borne by an altogether different comet, C/1974 V2. Discovered by John Caister Bennett on December 28, 1969 while still almost two AUs from the Sun, it reached perihelion on March 20, passing closest to Earth on March 26, 1970 as it receded, peaking at magnitude 0. It was last observed on February 27, 1971.

Observational history

The comet was discovered by John Caister Bennett on 28 December 1969 from Pretoria, South Africa, during his comet seeking routine. The comet was located in the costellation Tucana, in 65° south declination, and had an estimated magnitude of 8.5. At that time the comet was about 1.7 AU both from the Sun and the Earth. The orbit was computed by M. P. Candy of the Perth Observatory and it became apparent that the comet could became a bright object by the end of March, during its perihelion at a distance of 0.54 AU, as it moved northwards.

The comet became visible to the naked eye in February, and the first week of that month it had a magnitude of 5 and its tail measured about one degree in length. By the end of February the comet had brightened to a magnitude of 3.5 while its tail was about two degrees long. The comet continued to brighten during March, as it approached both the Sun and Earth. By the middle of the month it was a first magnitude with a prominent curved tail about 10 degrees long.

The comet reached perihelion on 20 March and crossed the equator on 25 March, becoming better visible in the morning sky of the north hemisphere, staying at an elongation greater than 32 degrees. On 26 March was the perigee of the comet, when it approached Earth at a distance of 0.69 AU. The comet was then at the square of the Pegasus and continued moving northwards until it reached its maximum north declination of 83° in August, when the comet was in the constellation of Camelopardalis. The comet at the start of April had a magnitude of 1, but as it receded both from the Sun and Earth, it had dimmed to a magnitude of 3-4 by the end of April, when its circumpolar, located in Cassiopeia. The comet had in April two tails, with the longest being 20-25 degrees long. Although by the start of May the comet head had faded to magnitude 5, its tail was still 10-15 degrees long, but by the end of the month it was only 2.5 degrees long. It was last seen by naked eye around mid May.

The comet was observed to fade during summer, autumn and winter. By the start of July it was around magnitude 10 and by the September it was magnitude 12. In January of 1971 it was photographed as a 18.9 magnitude object. It was last photographed by Elizabeth Roemer on 27 February 1971, when the comet was 4.9 AU from the Sun and 5.3 AU from Earth.

Scientific results

Soon after the first orbital elements could be calculated, it was suggested that the comet would become "a bright object, that could be observed with unaided eye." It was found to combine three favorable characteristics that made it an exceptional comet for observation: a short perihelion distance, a short distance from Earth, and high intrisic brightness. Numerous research projects were therefore initiated, so that Comet Bennett became the most photographed and most thoroughly researched comet at the time of its appearance.

Ultraviolet observations

A few years earlier it had been suggested that comets are surrounded by a shell of hydrogen gas, which could be detected by observing in the ultraviolet the Lyman α line at 121.5 nm. However, this observation is not possible from the ground because the ultraviolet light does not penetrate the atmosphere. The first observation of a comet in the ultraviolet came in January 1970 when the Orbiting Astronomical Observatory 2 (OAO-2) acquired the spectrum of comet C/1969 T1 (Tago-Sato-Kosaka) and verified the predicted hydrogen envelope. In February of the same year, Comet Bennett reached a favorable observation position for observation from space and was systematically observed with OAO-2 and OGO-5 on the basis of this discovery from mid-March to mid-April in order to track the temporal and spatial changes in the comet's coma.

From the photometric data obtained with OAO-2, the production rates of OH and H and their dependence on the comet's distance from the sun could be derived. The results confirmed the assumption that the gas production of comets at small solar distances is determined by the evaporation of water from the nucleus. The total loss of water during its passage through the inner solar system has been estimated at about 200 million tones.

The comet was also observed for the first time by the Orbiting Geophysical Observatory (OGO-5) on April 1 and 2. With a more sensitive photometer than with OAO-2, emissions from hydrogen atoms could be detected up to a distance of several million km from the comet's nucleus. From the measurements, the mass of this hydrogen could be derived at about 2 million tones. After these first successful measurements, it was decided to continue observing the comet with the instruments on board OGO-5 and thus a total of twelve intensity maps of the comet's Lyman-α emission were obtained by April 30. The maps show the evolution of the hydrogen envelope over the course of a month. On April 1, when the comet was about 0.6 AU from the Sun, the hydrogen envelope was 20 million km × 15 million km in size, after which it slowly began to shrink. The derived hydrogen atom production rate was comparable to the value obtained from the OAO-2 observations. In further investigations, attempts were then made to theoretically underpin the measurement results with greater agreement and to provide refined models for the formation of the hydrogen shells.

Visible light

At the Goddard Space Flight Center in Maryland, images of the comet were taken from March 28 to April 18, 1970 with interference filters at different wavelengths in the violet, blue, green, and yellow regions of the spectrum. In particular, the emission lines of CN, C2, CO+ and Na were evaluated. Maps of the comet's coma with lines of the same brightness (isophotes) up to a distance of 150,000 km from the nucleus were created from these and other images taken on April 8 and 9 at the Hamburg Observatory in white light. Similar surveys were also conducted from March 31 to April 27 at the University of Western Ontario's Hume Cronyn Memorial Observatory in Canada. There, too, images of the comet were taken with interference filters at different wavelengths in the violet, blue and green regions of the spectrum. In particular, the emission lines of CN and C2 were measured and their intensity profiles evaluated in parallel and perpendicular directions to the comet's tail and presented in the form of isophotes.

From March 30 to May 7, 1970, spectrographic studies of the comet were made at the Observatory of the University of Toledo in Ohio. In this way, brightness profiles of the emission lines of C2 and CN were obtained up to a distance of 100,000 km from the comet's nucleus. A brightness profile of the "forbidden" emission line of the oxygen atom at 630 nm was also created from images from April 18. It has been suggested that these atoms result from the decay of CO2 and that comet Bennett contained CO2 in excess of water. The same images were also used to create a brightness profile of the H₂O+ ion up to a distance of about 100,000 km from the nucleus and to determine its production rate. The results could later be revised through improved processing of the data.

From March 7 to 18, images of the comet were taken at the Cerro Tololo Inter-American Observatory in Chile. The comet's tail showed no noticeable disturbances, only pronounced side rays could be observed. This indicates that relatively quiet interactions between the solar wind and associated magnetic fields and the comet were occurring during this period.

Images taken from late March to late May at the Osservatorio Astrofisico di Asiago in Italy were evaluated for the distribution of gas and dust in Comet Bennett's tail. On the 3rd/4th of April, it was observed that the comet's gas tail had been torn off the coma. Spectra of the neutral gas envelope showed the emission lines of CN, C2, C3, CH, NH2 and Na. The gas tail showed a diurnal variation in intensity and structure, indicating a very erratic production of CO+. In particular, attempts were also made to correlate a prominent kink observed in the comet's gas tail on April 4 with simultaneous measurements of solar activity and solar wind. This was done using measurement data provided around the same time by the OGO-5, Vela 5, HEOS-1 and Pioneer 8 spacecraft, as well as by the ALSEP experiment installed on the lunar surface by Apollo 12. In a first investigation, no events were found in the measured dynamics of the solar wind that could explain the deformations of the comet's tail. However, further investigation concluded that, first, the dynamics of the solar wind measured near Earth were probably different from those near the comet, and second, the monitoring of the solar wind was patchy in terms of location and time, so that the deformations of the comet's tail can probably still be traced back to events in the solar wind.

Three images of the comet in red light, taken May 5-8 at the Thuringian State Observatory in Tautenburg, when the Earth was almost in the comet's orbital plane, showed two anomalous structures in the comet's tail: a radial structure and a short sunward spikes, probably caused by the comet's dust. The later evaluation of these observations provided evidence for the peculiarity of a "neckline structure" (NLS) in the dust tail of a comet, which was only theoretically derived in 1977.

Infrared

Observations of the comet's brightness evolution in the infrared were made in late March to mid-April 1970 at the Lunar and Planetary Laboratory in Arizona. In addition, on March 31, 1970, observations were made with an infrared telescope on board a Learjet.

On April 4, 1970, Comet Bennett was photometrically measured at the O'Brien Observatory of the University of Minnesota in the near and mid-infrared at 2-20 µm wavelength. In addition to the continuum of a black body of about 500 K at short wavelengths, an emission line could also be detected at 10 µm, which was traced back to silicate grains in the dust of the comet. The measurement result was confirmed by another measurement on April 21 at Kitt Peak National Observatory in Arizona.

Microwaves

With the radio telescope of the Green Bank Observatory in West Virginia, an attempt was made over six days in mid-March 1970 to detect the emission of formaldehyde at 4.83 GHz. Likewise, the radio telescope at the United States Naval Research Laboratory in Maryland attempted to detect the emission of water molecules at 22.2 GHz over four days at the end of March 1970. In both cases, no such emissions could be detected.

Apollo 13 attempted photograph

Comet Bennett was intended to be photographed by the crew of Apollo 13 during their journey to the Moon. Their first attempt on April 13, 1970 was unsuccessful. On April 14, 1970, after completing the maneuver to orient the spacecraft for a second attempt, Odyssey's service module ruptured, forcing the cancellation of the mission's scientific objectives and touchdown on the lunar surface.

References

1. Yeomans, Donald K. "Great Comets in History". ssd.jpl.nasa.gov. Retrieved 17 April 2023.
2. ^ C&MS: C/1969 Y1 (Bennett)
3. ^ Hendrie, M. J. (1 February 1999). "Comet Bennett 1969i". Journal of the British Astronomical Association. 109: 14–21. ISSN 0007-0297.
4. ^ "THE BRIGHT-COMET CHRONICLES". www.icq.eps.harvard.edu. Retrieved 12 February 2023.
5. ^ Marsden, B. G. (1 March 1971). "Comets in 1970". Quarterly Journal of the Royal Astronomical Society. 12: 244–273. ISSN 0035-8738.
6. Mobberley, Martin (2011). "Hunting and Imaging Comets". Springer: 64–66. doi:10.1007/978-1-4419-6905-7. {{cite journal}}: Cite journal requires |journal= (help)
7. A. D. Code, T. E. Houck, C. F. Lillie: Ultraviolet Observations of Comets. In: A. D. Code (Ed.): The Scientific Results from the Orbiting Astronomical Observatory (OAO-2). NASA Scientific and Technical Information Office, Washington D.C. 1972, NASA SP-310, S. 109–114 (PDF; 350 kB).
8. Lillie, C. F.; Keller, H. U. (1 January 1976). "The Gas Production Rate of Comet Bennett". NASA Special Publication. 393: 323.
9. Keller, H. U.; Lillie, C. F. (1 August 1974). "The Scale Length of OH and the Production Rates of H and OH in Comet Beunett (1970 II)". Astronomy and Astrophysics. 34: 187. ISSN 0004-6361.
10. J.-L. Bertaux, J. Blamont: Observation de l’émission d’hydrogène atomique de la comète Bennett. In: Comptes rendus hebdomadaires des séances de l'Académie des sciences. Vol. 270, Serie B, 1970, p. 1580–1584 (Archive link)
11. Bertaux, J. L.; Blamont, J. E.; Festou, M. (1 June 1973). "Interpretation of Hydrogen Lyman-Alpha Observations of Comets Bennett and Encke". Astronomy and Astrophysics. 25: 415–430. ISSN 0004-6361.
12. Keller, H. U. (1 August 1973). "Hydrogen Production Rates of Comet Bennett (1969i) in the First Hall of April 1970". Astronomy and Astrophysics. 27: 51. ISSN 0004-6361.
13. Keller, H. U.; Thomas, G. E. (1 February 1975). "A cometary hydrogen model: comparison with OGO-5 measurements of comet Bennett (1970 II)". Astronomy and Astrophysics. 39: 7–19. ISSN 0004-6361.
14. H. U. Keller, G. E. Thomas: A High-Velocity Component of Atomic Hydrogen in Comet Bennett (1970 II). In: B. D. Donn, M. Mumma, W. Jackson, M. A’Hearn, R. Harrington (Ed.): The Study of Comets. Part 1. The Proceedings of IAU Colloquium No. 25. NASA Scientific and Technical Information Office, Washington D. C. 1976, NASA SP-393, S. 316–321, Bibcode:1976NASSP.393..316K (PDF; 113 kB).
15. Rahe, J.; McCracken, C. W.; Donn, B. D. (1 January 1976). "Monochromatic and white-light observations of comet Bennett 1969i (1970 II)". Astronomy and Astrophysics Supplement Series. 23: 13–35. ISSN 0365-0138.
16. Borra, Ermanno F.; Wehlau, William H. (April 1971). "Narrow-Band Photometry of Comet Bennett (1969 i)". Publications of the Astronomical Society of the Pacific. 83: 184. doi:10.1086/129098.
17. Borra, Ermanno F.; Wehlau, William H. (October 1973). "Narrow-Band Isophotes of Comets Tago-Sato-Kosaka and Bennett". Publications of the Astronomical Society of the Pacific. 85: 670. doi:10.1086/129525.
18. Delsemme, A. H.; Moreau, J. L. (1 January 1973). "Brightness Profiles in the Neutral Coma of Comet Bennett (1970 II)". Astrophysical Letters. 14: 181. ISSN 0004-6388.
19. Delsemme, A. H.; Combi, M. R. (1 November 1976). "The Production Rate and Possible Origin of O ((1) d) in Comet Bennett 1970 II". The Astrophysical Journal. 209: L149. doi:10.1086/182286.
20. Delsemme, A. H.; Combi, M. R. (1 November 1976). "Production Rate and Origin of H20(+) in Comet Bennett 1970 II". The Astrophysical Journal. 209: L153. doi:10.1086/182287.
21. Delsemme, A. H.; Combi, M. R. (February 1979). "O/1D/ and H2O/+/ in comet Bennett 1970. II". The Astrophysical Journal. 228: 330. doi:10.1086/156850.
22. Miller, Freeman D. (September 1992). "The side-ray systems of Comet Bennett, 1970 March 7-18". The Astronomical Journal. 104: 1207. doi:10.1086/116309.
23. Wurm, Karl; Mammano, Augusto (October 1972). "Contributions to the kinematics of type I tails of comets". Astrophysics and Space Science. 18 (2): 273–286. doi:10.1007/BF00645393.
24. Wurm, Karl; Mammano, Augusto (October 1972). "The motion of dust and gas in the heads of comets with type II tails". Astrophysics and Space Science. 18 (2): 491–503. doi:10.1007/BF00645412.
25. Burlaga, L. F.; Rahe, J.; Donn, B.; Neugebauer, M. (May 1973). "Solar wind interaction with Comet Bennett (1969i)". Solar Physics. 30 (1): 211–222. doi:10.1007/BF00156190.
26. Jockers, K.; Lust, Rh. (1 July 1973). "Tail Peculiarities in Comet Beunett Caused by Solar Wind Disturbances". Astronomy and Astrophysics. 26: 113. ISSN 0004-6361.
27. Pansecchi, L.; Fulle, M.; Sedmak, G. (1 April 1987). "The nature of two anomalous structures observed in the dust tail of Comet Bennett 1970. II - A possible Neck-Line Structure". Astronomy and Astrophysics. 176: 358–366. ISSN 0004-6361.
28. Kleinmann, D. E.; Lee, T.; Low, F. J.; O'dell, C. R. (May 1971). "Infrared Observations of Comets 1969g and 1969i". The Astrophysical Journal. 165: 633. doi:10.1086/150927.
29. Maas, R. W.; Ney, E. P.; Woolf, N. J. (May 1970). "The 10-MICRON Emission Peak of Comet Bennett 1969i". The Astrophysical Journal. 160: L101. doi:10.1086/180537.
30. Hackwell, J. A. (1 February 1971). "10 micron emission spectrum of Comet Bennett". The Observatory. 91: 33–34. ISSN 0029-7704.
31. Huebner, Walter F.; Snyder, Lewis E. (September 1970). "Radio Search for Formaldehyde in Comet Bennett (1969i)". The Astronomical Journal. 75: 759. doi:10.1086/111021.
32. Clark, T. A.; Donn, B.; Jackson, W. M.; Sullivan, W. T., Iii; Vandenberg, N. (September 1971). "Search for Microwave H20 Emission in Comet Bennett (1969i)". The Astronomical Journal. 76: 614. doi:10.1086/111171.{{cite journal}}: CS1 maint: multiple names: authors list (link)
33. "Apollo Expeditions to the Moon: Chapter 13". history.nasa.gov. Retrieved 2015-06-05.
34. Apollo 13 Accident – Flight Director Loop Part 1, retrieved 2015-06-05

External links

• Cometography.com
• Orbital simulation from JPL (Java) / Ephemeris

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P1 (2007) 103P/Hartley (2010) 67P/Churyumov–Gerasimenko (2014) Near-Parabolic comets (notable) Until 1990 C/-43 K1 (Caesar's Comet) X/1106 C1 (Great Comet of 1106) C/1264 N1 (Great Comet of 1264) C/1402 D1 (Great Comet of 1402) C/1471 Y1 (Great Comet of 1472) C/1577 V1 (Great Comet of 1577) C/1652 Y1 C/1680 V1 (Great Comet of 1680, Kirsch's Comet, Newton's Comet)) C/1702 H1 (Comet of 1702) C/1729 P1 (Comet of 1729, Comet Sarabat) C/1743 X1 (Great Comet of 1744, Comet Klinkenberg-Chéseaux) C/1760 A1 (Great Comet of 1760) C/1769 P1 (Great Comet of 1769) C/1807 R1 (Great Comet of 1807) C/1811 F1 (Great Comet of 1811) C/1819 N1 (Great Comet of 1819) C/1823 Y1 (Great Comet of 1823) C/1843 D1 (Great March Comet of 1843) C/1847 T1 (Miss Mitchell's Comet) C/1858 L1 (Comet Donati) C/1861 G1 (Comet Thatcher) C/1861 J1 (Great Comet of 1861) C/1865 B1 (Great Southern Comet of 1865) X/1872 X1 (Pogson's Comet) C/1874 H1 (Comet Coggia) C/1881 K1 (Comet Tebbutt) C/1882 R1 (Great Comet of 1882) C/1887 B1 (Great Southern Comet of 1887) C/1901 G1 (Great Comet of 1901) C/1910 A1 (Great January Comet of 1910) C/1911 O1 (Brooks) C/1911 S3 (Beljawsky) C/1927 X1 (Skjellerup–Maristany) C/1931 P1 (Ryves) C/1941 B2 (de Kock-Paraskevopoulos) C/1947 X1 (Southern Comet) C/1948 V1 (Eclipse) C/1956 R1 (Arend–Roland) C/1957 P1 (Mrkos) C/1961 O1 (Wilson-Hubbard) [de] C/1961 R1 (Humason) C/1962 C1 (Seki-Lines) C/1963 A1 (Ikeya) C/1963 R1 (Pereyra) C/1964 N1 (Ikeya) C/1965 S1 (Ikeya-Seki) C/1969 T1 (Tago-Sato-Kosaka) [de] C/1969 Y1 (Bennett) C/1970 K1 (White–Ortiz–Bolelli) C/1973 E1 (Kohoutek) C/1975 V1 (West) C/1980 E1 (Bowell) C/1983 H1 (IRAS–Araki–Alcock) C/1989 W1 (Aarseth-Brewington) C/1989 X1 (Austin) C/1989 Y1 (Skorichenko–George) After 1990 C/1990 K1 (Levy) C/1992 J1 (Spacewatch–Rabinowitz) C/1993 Y1 (McNaught–Russell) C/1995 O1 (Hale–Bopp) C/1996 B2 (Hyakutake) C/1997 L1 (Zhu–Balam) C/1998 H1 (Stonehouse) C/1998 J1 (SOHO) C/1999 F1 (Catalina) C/1999 S4 (LINEAR) C/2000 WM1 (LINEAR) C/2001 A2 (LINEAR) C/2001 OG108 (LONEOS) C/2001 Q4 (NEAT) C/2002 T7 (LINEAR) C/2002 V1 (NEAT) C/2004 F4 (Bradfield) C/2004 Q2 (Machholz) C/2006 A1 (Pojmański) C/2006 M4 (SWAN) C/2006 P1 (McNaught) C/2007 E2 (Lovejoy) C/2007 F1 (LONEOS) C/2007 N3 (Lulin) C/2007 Q3 (Siding Spring) C/2007 W1 (Boattini) C/2009 F6 (Yi–SWAN) C/2009 R1 (McNaught) C/2010 X1 (Elenin) C/2011 L4 (PANSTARRS) C/2011 W3 (Lovejoy) C/2012 E2 (SWAN) C/2012 F6 (Lemmon) C/2012 K1 (PANSTARRS) C/2012 S1 (ISON) C/2013 A1 (Siding Spring) C/2013 R1 (Lovejoy) C/2013 US10 (Catalina) C/2013 V5 (Oukaimeden) C/2014 E2 (Jacques) C/2014 Q1 (PanSTARRS) C/2014 Q2 (Lovejoy) C/2015 ER61 (PanSTARRS) C/2015 V2 (Johnson) C/2017 K2 (PanSTARRS) 1I/2017 U1 ʻOumuamua C/2018 Y1 (Iwamoto) 2I/Borisov C/2019 U6 (Lemmon) C/2019 Y4 (ATLAS) C/2020 F3 (NEOWISE) C/2020 F8 (SWAN) C/2021 A1 (Leonard) C/2022 E3 (ZTF) C/2023 A3 (Tsuchinshan–ATLAS) C/2023 P1 (Nishimura) After 1910 (by name) Aarseth-Brewington Arend–Roland Austin Beljawsky Bennett Boattini Borisov Bowell Bradfield Brooks Catalina C/1999 F1 C/2013 US10 de Kock–Paraskevopoulos Eclipse Elenin Hale-Bopp Humason Hyakutake Ikeya C/1963 A1 C/1964 N1 Ikeya-Seki IRAS–Araki–Alcock ISON Iwamoto Jacques Johnson Kohoutek Lemmon C/2012 F6 C/2018 C2 C/2019 U6 Leonard Levy LINEAR C/1999 S4 C/2000 WM1 C/2001 A2 C/2002 T7 LONEOS C/2001 OG108 C/2007 F1 Lovejoy C/2007 E2 C/2011 W3 C/2013 R1 C/2014 Q2 Lulin Machholz McNaught C/2006 P1 C/2009 R1 McNaught–Russell Mrkos NEAT C/2001 Q4 C/2002 V1 NEOWISE Nishimura Oukaimeden ʻOumuamua Pan-STARRS C/2011 L4 C/2012 K1 311P/PanSTARRS C/2014 Q1 C/2015 ER61 C/2017 K2 Pereyra Pojmański Ryves Seki–Lines Siding Spring C/2007 Q3 C/2013 A1 Skjellerup–Maristany Skorichenko–George SOHO Southern Spacewatch–Rabinowitz Stonehouse SWAN C/2006 M4 C/2012 E2 C/2020 F8 Tago-Sato-Kosaka [de] Tsuchinshan–ATLAS West White–Ortiz–Bolelli Wilson–Hubbard [de] Yi–SWAN Zhu–Balam ZTF
Category

• Long-period comets
• Great comets
• Discoveries by amateur astronomers
• Astronomical objects discovered in 1969
• 1969 in science
• 1970 in science