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Comet ISON
Comet ISON, formally known as C/2012 S1, was a sungrazing comet discovered on 21 September 2012 by Vitali Nevski (Виталий Невский, Vitebsk, Belarus) and Artyom Novichonok (Артём Новичонок, Kondopoga, Russia).〔 The discovery was made using the reflector of the International Scientific Optical Network (ISON) near Kislovodsk, Russia.〔 Data processing was carried out by automated asteroid-discovery program CoLiTec.〔 Precovery images by the Mount Lemmon Survey from 28 December 2011 and by Pan-STARRS from 28 January 2012 were quickly located.〔 Follow-up observations were made on 22 September by a team from Remanzacco Observatory in Italy using the iTelescope network.〔〔 The discovery was announced by the Minor Planet Center on 24 September.〔 Observations by Swift in January 2013 suggested that Comet ISON's nucleus was around in diameter.〔 Later estimates were that the nucleus was only about in diameter.〔 Mars Reconnaissance Orbiter (MRO) observations suggested the nucleus was smaller than in diameter.〔
Shortly after Comet ISON's discovery, the media reported that it might become brighter than the full moon. However, as events transpired, it never became bright enough to be readily visible to the naked eye. Furthermore, it broke apart as it passed close to the Sun. Reports on 28 November 2013 (the day of perihelion passage)〔〔 indicated that Comet ISON had partially or completely disintegrated due to the Sun's heat and tidal forces. However, later that day CIOC (NASA ''C''omet ''I''SON ''O''bserving ''C''ampaign) members discovered a coma-like feature, suggesting a small fragment of it may have survived perihelion.〔〔〔 On 29 November 2013, the coma dimmed to an apparent magnitude of 5.〔 By the end of 30 November 2013, the coma had further faded to below naked-eye visibility at magnitude 7.〔 On 1 December, the coma continued to fade even further as it finished traversing the Solar and Heliospheric Observatory's view.〔 On 2 December 2013, the CIOC announced that Comet ISON had fully disintegrated.〔〔 The Hubble Space Telescope failed to detect fragments of ISON on 18 December 2013.〔 On 8 May 2014, a detailed examination of the disintegration was published, suggesting that the comet fully disintegrated hours before perihelion.〔
==Discovery==
During routine observations on 21 November 2012, Vitali Nevski and Artyom Novichonok monitored areas of Gemini and Cancer after their observations were delayed by clouded weather for much of the night. The team used ISON's reflector near Kislovodsk, Russia and CCD imaging to carry out their observations. Shortly after their session, Nevski processed data using CoLiTec, an automated asteroid discovery software program. In analysis he noted an unusually bright object with slow apparent movement, indicating a position outside the orbit of Jupiter based on the use of four 100-second CCD exposures.〔 At the time of discovery, the object's apparent magnitude ranged from 19.1 to as bright as 18.8.〔Astronomical magnitudes decrease as brightness increases, from large positive values, through zero, to negative values for very bright objects.〕
The group reported their discovery to the Central Bureau for Astronomical Telegrams as an asteroidal object, which was subsequently forwarded to the Minor Planet Center. However, the group later reported that the object had a cometary appearance with a coma approximately 8 arcseconds across. The object's position and cometary appearance was confirmed by several other unaffiliated observers, and as such the comet was named ''ISON'', after the international observational project and in accordance with International Astronomical Union naming guidelines.〔〔 Comet ISON was precovered in analysis of Mount Lemmon Observatory imagery by G.V. Williams and Pan-STARRS imagery in Haleakalā. Precovery images from Mount Lemmon were first taken on 28 December 2011 and indicated that the comet had an estimated apparent magnitude ranging from 19.5 to 19.9. Images from Pan-STARRS were taken on 28 January 2012 and in those images the comet had an estimated apparent magnitude ranging from 19.8 to 20.6.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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