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C/2012 S1 (ISON)

Orbit by Kazuo Kinoshita

Morning sky plots of the comet's position in December


Image of comet ISON on 2013 November 15
Copyright © 2013 by Damian Peach (Selsey, West Sussex, England)

This image was acquired on 2013 November 15, using a 11-cm telescope and an STL-11k CCD camera. Several exposures using various filters were combined to make this color image, with the total exposure time amounting to 12 minutes.

Latest News (Updated November 30, 2013 @ 20:49 UT)

  • Comet C/2012 S1 (ISON) was closest to the Sun on November 28. Within a week of the comet's discovery during September 2012 there was speculation that the comet might become visible in broad daylight. This did not to happen. Visual and photographic observations of the comet from Earth ended as the comet moved into bright twilight after November 23; however, observations continued thanks to the STEREO and SOHO spacecraft which orbit the Sun and continuously monitor the Sun and the region surrounding it. These revealed that the comet faded as it approached its closest distance from the Sun, seeming to almost vanish. The comet did brighten within a few hours after perihelion and was seemingly healthy again during November 29; however, as November 30 arrived, the comet was again not looking very good and, as the image below shows, it seems to be nothing more than a dissipating cloud of dust.
  • Image of comet ISON on 2013 November 30
    Copyright © 2013 by NASA/SOHO

    This image was acquired on 2013 November 30 at about 19:42 UT by the Solar and Heliospheric Observatory (SOHO) spacecraft using the Large Angle and Spectrometric Coronagraph (LASCO) C3 camera. The remnants of the comet are near the top of the image.

    Discovery

    Vitali Nevski and Artyom Novichonok were expecting to use the International Scientific Optical Network's (ISON) 40-cm reflector at Kislovodsk Observatory (Russia) on the night of 2012 September 20/21, but clouds halted their plans...at least for most of the night. About a half hour prior to the beginning of morning twilight, they noticed the sky was clearing and got the telescope and CCD camera up and running to obtain some survey images in the Gemini and Cancer region. After twilight began, Novichonok left to get some rest, while Nevski loaded the images into a program called CoLiTec, which is designed to detect asteroids and comets moving between images. Nevski noted a rather bright object with unusually slow movement, which he thought could only mean it was situated beyond the orbit of Jupiter. The images showing the object were all acquired during the period of September 21.05-21.07. Notice of the discovery was sent to the Central Bureau for Astronomical Telegrams, which immediately placed the object on the NEOCP web page of the Minor Planet Center, so that other observers could obtain confirming images. It was then uncertain whether the object was a minor planet or a comet. Novichonok booked time on the 1.5-m reflector at Majdanak Observatory (Uzbekistan) and O. Burhonov answered the call by acquiring images on September 21.99. Although these new images revealed Nevski and Novichonok had discovered a comet, other observers following up on the NEOCP web site had already reported the cometary appearance, so the comet was named ISON, instead of being named after the discoverers.

    Image of the discoverers of comet ISON
    Copyright © 2012 by A. Novichonok (ISON-Kislovodsk Observatory, Russia)

    This is an image of the discoverers of comet ISON. Artyom Novichonok is on the left and Vitali Nevski is on the right.


    Image of comet ISON on 2012 September 21
    Copyright © 2012 by V. Nevski and A. Novichonok (ISON-Kislovodsk Observatory, Russia)

    This is very first image that was acquired by Nevski and Novichonok on 2012 September 21.05. The comet is in the middle of the circle.


    Prediscovery images were found by G. V. Williams (in the survey archives of the Mount Lemon Survey (Arizona, USA) and Pan-STARRS 1 (Haleakala, Hawaii, USA). The three Mount Lemon images were obtained using the 1.5-m reflector and a CCD camera during 2011 December 28.35-28.38 and revealed a magnitude range of 19.5-19.9. The three Pan-STARRS 1 images were obtained using the 1.8-m refelctor and a CCD camera during 2012 January 28.45-28.50 and indicated a magnitude range of 19.8-20.6.


    Early Orbit Calculations

    While on the NEOCP web page, the object was designated AS03D20. Maik Meyer (Germany) took an interest in this object and began calculating orbits. He published his first orbit on the "comets-ml" group on Yahoo on 2012 September 23 at 10:29 UT. This used 33 positions spanning September 21-23, giving the perihelion date as 2013 October 19.62 and the perihelion distance as 0.03 AU. The latter number was enough for Meyer to include the text "Something to dream of?" At 15:59 UT, Meyer sent a revised orbit to "comets-ml" which used 40 positions from September 21-23. The perihelion date was given as 2013 November 14.97, while the perihelion distance was 0.01 AU. He commented, "still looks good. There is a q=2.x solution but with T in 2010, so I still would bet a few Euro's on the low-q solution." Meyer's final orbit came nearly 24 hours later, when he announced on the "comets-ml" group that 50 positions spanning September 21-24 indicated a perihelion date of 2013 November 1.03 and a perihelion distance of 0.02 AU. Later that same day, at 18:40 UT, the Minor Planet Center sent a notice which provided all available observations of this comet, including the prediscovery images received from Mount Lemon and Pan-STARRS 1. The resulting orbit used 54 positions spanning 2011 December 28 to 2012 September 23, giving the perihelion date as 2013 November 28.87 and the perihelion distance as 0.012 AU. We now know that the comet passed perihelion on November 28.78 at a distance of 0.012 AU. The comet seems to be fresh from the Oort cloud, meaning that this is likely the first time it has approached the Sun since the birth of our solar system.

    Speculation

  • Although this comet was over a year from passing closest to the sun, there was a lot of speculation during the first week following its discovery. Here are a few of the details:

    *Several people have suggested the comet might reach a maximum magnitude of -6 to -10 when the comet is closest to the sun, which would enable it to be seen in broad daylight. As of 2012 September 25, the Central Bureau for Astronomical Telegrams web site indicated a maximum brightness of -13.1 on 2013 November 28 at 21:00 UT.
    *J. E. Bortle (New York, USA) wrote the following, "based on the development of past major comets with perihelia less than 0.1 AU, together with the earth-comet-sun alignment of 2012 S1 during early to mid December of 2013, and assuming a typical rate of dust production, that the dust tail generated by 2012 S1 might be among the longest ever recorded."
    *Reinder J. Bouma (Netherlands) first pointed out on 2012 September 24 that the orbit of this is "somewhat similar" to the orbit of the great comet of 1680. Others have suggested the possibility that the 1680 comet and this new comet might have split in the distant past.
    Concerning the first two points, all have suggested caution until more is known about this comet. In particular, Bortle noted the past incidences of the last few decades, when comets failed to live up to the early expectations. Only time will tell.

  • Will the comet hold together?

  • Astronomer Ignacio Ferrin (Columbia) has published a prediction that comet ISON may be on the verge of disingrating. The prediction was not made using a crystal ball, but using comet research spanning several years. Over a decade ago, Ferrin came up with a new way of studying the brightness behavior of comets. He recently applied this to comet ISON and found an unusual brightness "discontinuity" when the comet was near Jupiter earlier this year. Looking through his analyses of 87 other comets, Ferrin found only two other comets that have shown this same behavior: comet Tabur of 1996 and comet Honig of 2002. Both of these comets disintegrated, hence his recent prediction. The fact that so many observers are now following this comet offers an excellent chance to test Ferrin's prediction. If the comet does indeed break up, it will be the most studied comet event of this kind ever, perhaps allowing astronomers to better understand these events and comets in general. If it does not break up, Ferrin goes back to the drawing board to tweak his theory.
  • Two more papers have been submitted to various journals that give a more optimistic prediction for comet ISON. Zdenek Sekanina has conducted an analysis of comet ISON compared to two other comets which were fresh from the Oort cloud. One comet, Seki-Lines, performed quite well during 1962, while the other comet, Honig, disintegrated during 2002. He finds comet ISON to be performing closer to comet Seki-Lines. Matthew Knight and Kevin Walsh compared comet ISON to other sungrazing comets. Although there were an number of parameters about comet ISON that are currently unknown, they predicted that "tidal disruption [is] unlikely unless other factors affect ISON substantially." One of these factors was a possible speeding up of the rotation of the nucleus.
  • Observations

  • The first independent confirmation of this comet's discovery came from W. H. Ryan and E. V. Ryan (Magdalena Ridge Observatory, Socorro, New Mexico, USA) on September 21.42. They were using the 2.4-m reflector and a CCD camera. The comet's magnitude was given as 17.5.
  • Although the comet steadily brightened as expected during the remainder of 2012, it was expected to slow down during the early months of 2013, as Earth's motion around its orbit was putting a lot of distance between it and the comet. After Earth reached the point in its orbit when it was on the other side of the Sun from the comet, the distance between the two bodies began to decrease. Although the comet was expected to resume its brightening, it did not. In fact, during the period of January through June, the comet may have actually faded slightly, making it almost two magnitudes fainter than predicted by the beginning of July. This indicates the comet's activity level has decreased during a time when it should be increasing.
  • The comet dropped into evening twilight near the end of June 2013 and was recovered in August. The first reported observation was possibly made from southeastern Arizona (USA), when an amateur astronomer used a video camera attached to a telescope and stacked several of the frames. The comet would have been at a very low elevation above the horizon (he Author has yet to see this image and considers the observation as uncertain for now). The first definite observation was obtained by Bruce Gary (Hereford Arizona Observatory, Arizona, USA) on August 12.5.
  • Visual observers were placing the brightness of comet ISON at about magnitude 12 during the first week of September. The coma was about 2' across and slightly condensed. The comet attained a magnitude of about 11 during the first week of October. The coma was then about 3' across and moderately condensed. Jakub Cerny (Czech Republic) noted a tail extending 0.1 degree toward a position angle of 300 degrees on October 2 and 4, while using his 35-cm reflector.
  • Visual observers placed the brightness of comet ISON at about magnitude 10 during the final days of October. The coma was variously estimated as 3-4 arc minutes across and slightly condensed. A faint taillike extension was noted by several observers. During November 1-3, visual observers using binoculars were reporting a magnitude of 9 and a coma 4-5 arc minutes across. The coma was moderately condensed and a tail was detected toward the west-northwest.
  • On November 4, Sekanina provided a status report in the paper that was mentioned above. He stated that the comet's intrinsic brightness had stagnated since October 13. Interestingly, on November 6, C. Opitom, E. Jehin, J. Manfroid, and M. Gillon (Liege University) reported that they had been making observations of this comet using the robotic TRAPPIST telescope at La Silla Observatory (Chile) since October 12. They noted that activity levels had been stable until about November 3, when the gas production rates started to rapidly increase. They added that dust production has not increased during this time and they do not suspect that the comet is disrupting. They do suggest this might be due to a "deeper layer of ices" that have begun to sublimate. In addition, cyanogen and diatomic carbon filters are now revealing two jets extending from the nucleus.
  • Comet ISON experienced an outburst in brightness sometime during November 13/14. The increase in brightness amounted to 2 magnitudes and was accompanied by a more complex tail. One observer, Alexandre Amorim (Florianopolis, Brazil) gave the magnitude as 7.8 on November 13.30 and 6.1 on November 14.30, while using a 7-cm refractor. Chris Wyatt (Walcha, New South Wales, Australia) observed using 11x70 binoculars on November 13.72 and gave the magnitude as 7.4. He switched to 10x50 binoculars on November 14.71 and gave the magnitude as 5.3. Wyatt also noted the comet was visible to the naked eye on the last date. All observers have noted that the coma became more condensed as a result. The brightening seems to have continued into November 15. On November 15.44, Han Chen (Fairfax, Virginia, USA) said the comet was magnitude 4.8 in 7x50 binoculars, while, on November 15.50, Alan Hale (Mew Mexico, USA) observed with 10x50 binoculars and gave the same magnitude. Although the comet seemed to fade slightly during the next few days, as it dropped deeper into morning twilight, a few observers on November 21 were estimating magnitudes around 4. A disconnection event was also brought to the attention of observers by Denis Buczynski on the 21st. The comet's distance from the Sun was continuing to decrease and was situated only 20 degrees away on November 22.
  • The comet was located only 10 degrees from the Sun on November 26.
  • Additional Images

    Image of comet ISON on 2012 September 22
    Copyright © 2011 by E. Guido, G. Sostero, and N. Howes (Michelago, New South Wales, Australia)

    This image was acquired on 2012 September 22.5 (UT), while remotely using a 25-cm reflector and CCD camera at the RAS Observatory near Mayhill, New Mexico, USA. It is a stack of twenty-four 120-second exposures. This reveals a slightly diffuse object with a coma 5 arc seconds across.


    Image of comet ISON on 2012 September 24
    Copyright © 2012 by Michael Jäger (Austria)

    This image was acquired on 2012 September 24, using a 25-cm reflector and an FLI 8300 CCD camera. Four 7.5-minute exposures were combined to make this image.


    Image of comet ISON on 2013 January 16
    Copyright © 2013 by R. Ligustri (Italy)

    This image was acquired on 2013 January 16, using the remote 45-cm reflector and an FLI PL6303E CCD camera at Mayhill, New Mexico. The comet is indicated by the tick marks to the right of the middle of the image. [This is a crop of the original image]


    Image of comet ISON on 2013 June 13
    Copyright © 2013 by NASA/JPL-Caltech/JHUAPL/UCF

    These images from NASA's Spitzer Space Telescope of C/2012 S1 (Comet ISON) were taken on June 13, when ISON was 310 million miles (about 500 million kilometers) from the sun. The images were taken with the telescope's infrared array camera at two different near-infrared wavelengths, 3.6 and 4.5 microns (the representational colors shown were selected to enhance visibility). The 3.6-micron image on the left shows a tail of fine rocky dust issuing from the comet and blown back by the pressure of sunlight as the comet speeds towards the sun (the tail points away from the sun). The image on the right side shows the 4.5-micron image with the 3.6-micron image information (dust) removed, and reveals a very different round structure -- the first detection of a neutral gas atmosphere surrounding ISON. In this case, it is most likely created by carbon dioxide that is "fizzing" from the surface of the comet at a rate of about 2.2 million pounds (1 million kilograms) a day. According to the Spitzer web site, the observations revealed "what most likely are strong carbon dioxide emissions." At a distance of 312 million miles (502 million kilometers) from Earth, the indicated tail length was 186,400 miles (300,000 kilometers) long.


    Image of comet ISON on 2013 September 25
    Copyright © 2013 by Rolando Ligustri (Italy)

    This image was acquired on 2013 September 25, using the remote 45-cm reflector and an FLI PL6303E CCD camera at Mayhill, New Mexico. This was a 25-minute exposure.[This is a crop of the original image]


    Image of comet ISON on 2013 September 28
    Copyright © 2013 by Rolando Ligustri (Italy)

    This images was acquired by Ligustri on 2013 September 28. The image reveals Mars in the lower right quadrant, comet ISON in the upper right quadrant, and the asteroid 433 Eros on the left side of the image.


    Image of comet ISON on 2013 September 29
    Copyright © 2013 by NASA/JPL/University of Arizona

    These images were acquired by the Mars Reconnaissance Orbiter on 2013 September 29, when comet ISON was located about 8 million miles from the planet Mars.


    Image of comet ISON on 2013 October 3
    Copyright © 2013 by Martin P. Mobberley (England)


    Image of comet ISON on 2013 October 5
    Copyright © 2013 by Michael Jäger (Austria)

    This image was acquired on 2013 October 5, using a 20-cm reflector and an ASA SXV-H9 CCD camera. Several exposures using various filters were combined to make this color image, with the total exposure time amounting to 63 minutes.


    Image of comet ISON on 2013 October 8
    Copyright © 2013 by Adam Block (Mount Lemmon SkyCenter, University of Arizona, USA)

    This image was acquired on 2013 October 8, using an 81-cm reflector and an SBIG STX16803 CCD camera. Several exposures using various filters were combined to make this color image, with the total exposure time amounting to 52 minutes.


    Image of comet ISON on 2013 October 31
    Copyright © 2013 by Martin P. Mobberly (England)


    Image of comet ISON on 2013 October 31
    Copyright © 2013 by Michael Jäger (Austria)

    This image was acquired on 2013 October 31, using a 20-cm reflector and an FLI 8300 CCD camera. Several exposures using various filters were combined to make this color image, with the total exposure time amounting to 20 minutes.


    Image of comet ISON on 2013 October 31
    Copyright © 2013 by Martin P. Mobberly (England)


    Image of comet ISON on 2013 November 1
    Copyright © 2013 by Denis Buczynski (Tarbatness Observatory, Portmahomack, Scotland)


    Image of comet ISON on 2013 November 1
    Copyright © 2013 by Martin P. Mobberly (England)


    Image of comet ISON on 2013 November 6
    Copyright © 2013 by Damian Peach (Selsey, West Sussex, England)

    This image was acquired on 2013 November 6, using a 43-cm reflector and an FLI-PL6303e CCD camera. Several exposures using various filters were combined to make this color image, with the total exposure time amounting to 19 minutes.


    Image of comet ISON on 2013 November 8
    Copyright © 2013 by Adam Block (Mount Lemmon SkyCenter, University of Arizona, USA)

    This image was acquired on 2013 November 8, using an 81-cm reflector and an SBIG STX16803 CCD camera. Several exposures using various filters were combined to make this color image, with the total exposure time amounting to 36 minutes.


    Image of comet ISON on 2013 November 10
    Copyright © 2013 by Damian Peach (Selsey, West Sussex, England)

    This image was acquired on 2013 November 10, using a 11-cm telescope and an STL-11k CCD camera. Several exposures using various filters were combined to make this color image, with the total exposure time amounting to 18 minutes.


    Image of comet ISON on 2013 November 15
    Copyright © 2013 by Erik Bryssinck (BRIXIIS Observatory, Belgium)

    This image was acquired on 2013 November 15, using a 0.4-m astrograph and a CCD camera. The exposure time was 3 minutes.


    Image of comet ISON on 2013 November 20
    Copyright © 2013 by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Southwest Research Institute

    This image was acquired on 2013 November 20 by the Messenger spacecraft (in orbit around the planet Mercury) using the Wide Angle Camera of the Mercury Dual Imaging System. The comet was then at its closest distance from Mercury, which was about 22.5 million miles (36.2 million kilometers).


    Image of comet ISON on 2013 November 20
    Copyright © 2013 by José J. Chambó (La Llosa de Ranes, Valencia, Spain)

    This image was acquired on 2013 November 20, using a 20-cm reflector and a Canon EOS 350D camera. Fifteen 25-second exposures at ISO 800 were combined to create this image.


    Image of comet ISON on 2013 November 21
    Copyright © 2013 by Gerald Rhemann (Austria)

    This image was acquired on 2013 November 21 while Rhemann was visiting Namibia in Africa. It was acquired usng an ASA 31-cm astrograph and an FLI ML 8300 CCD camera. Four total exposures were combined to produce this color image: a 3-minute exposure with an L filter and separate 2-minute exposures with R, G, and B filters. Rhemann said the skies were excellent, which accounts for the excellent photo despite the fact that the first exposure was obtained when the comet was only about 1.5 degrees above the horizon, while the last was made when the comet was at an altitude of only 5 degrees.


    Image of comet ISON on 2013 November 22
    Copyright © 2013 by Michael Jäger (Austria)

    This image was acquired on 2013 November 22 at 5:00 UT, using a 8-cm APO refractor and an Kai 11002 CCD camera, as well as an 18-cm APO refractor and a KAF 6300 CCD camera. Several exposures using various filters were combined to make this color image, with the total exposure time amounting to nearly 10 minutes.


    Image of comet ISON on 2013 November 22
    Copyright © 2013 by NASA/STEREO

    This image was acquired on 2013 November 22 at 5:29 UT by the STEREO Ahead spacecraft using the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) hi1 camera. The image shows the present locations of the planets Mercury and Earth, as well as two comets. Comet ISON is the brightest, with bright tail extending toward the left. Comet Encke is a periodic comet that returns every 3.3 years and is displaying a very faint tail toward the left.


    Image of comet ISON on 2013 November 23
    Copyright © 2013 by NASA/STEREO

    This image was acquired on 2013 November 23 at 5:29 UT by the STEREO Ahead spacecraft using the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) hi1 camera. The image shows the present locations of the planets Mercury and Earth, as well as two comets. Comet ISON is the brightest, with bright tail extending toward the left. Comet Encke is a periodic comet that returns every 3.3 years and is displaying a very faint tail toward the left.


    Image of comet ISON on 2013 November 23
    Copyright © 2013 by Pete Lawrence (Roques de los Muchachos Observatory, La Palma, Canary Islands)

    This image was acquired on 2013 November 23 at about 6:30 UT, using the 254-cm Isaac Newton Telescope and a Canon 40D camera. This is a 30-second exposure at ISO 400.


    Image of comet ISON on 2013 November 24
    Copyright © 2013 by NASA/STEREO

    This image was acquired on 2013 November 24 at 5:29 UT by the STEREO Ahead spacecraft using the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) hi1 camera. The image shows the present locations of the planets Mercury and Earth, as well as two comets. Comet ISON is the brightest, with bright tail extending toward the left. Comet Encke is a periodic comet that returns every 3.3 years and is displaying a very faint tail toward the left.


    Image of comet ISON on 2013 November 25
    Copyright © 2013 by NASA/STEREO

    This image was acquired on 2013 November 25 at 5:29 UT by the STEREO Ahead spacecraft using the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) hi1 camera. The image shows the present locations of the planets Mercury and Earth, as well as two comets. Comet ISON is the brightest, with bright tail extending toward the left. Comet Encke is a periodic comet that returns every 3.3 years and is displaying a very faint tail toward the left.


    Image of comet ISON on 2013 November 27
    Copyright © 2013 by NASA/SOHO

    This image was acquired on 2013 November 27 at 13:30 UT by the Solar and Heliospheric Observatory (SOHO) spacecraft using the Large Angle and Spectrometric Coronagraph (LASCO) C3 camera. The image shows comet ISON toward the far right.


    Image of comet ISON on 2013 November 28
    Copyright © 2013 by NASA/SOHO

    This image was acquired on 2013 November 28 at 0:54 UT by the Solar and Heliospheric Observatory (SOHO) spacecraft using the Large Angle and Spectrometric Coronagraph (LASCO) C3 camera.


    Image of comet ISON on 2013 November 28
    Copyright © 2013 by NASA/SOHO

    This image was acquired on 2013 November 28 at 21:48 UT by the Solar and Heliospheric Observatory (SOHO) spacecraft using the Large Angle and Spectrometric Coronagraph (LASCO) C2 camera.

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