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Comet ISON (アイソン彗星) (C/2012 S1)


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アイソン彗星(アイソンすいせい、ISON)とは、彗星の1つ。
彗星の命名規則による仮符号はC/2012 S1。

発見
アイソン彗星は2012年9月21日にキスロヴォツク天文台 (Kislovodsk Observatory) にてヴィタリー・ネフスキー (Vitaly Nevsky) とアルチョム・ノヴィチョノク (Artem Novichonok) によって発見された。
名前は発見者が所属しているチーム、国際科学光学ネットワーク (International Scientific Optical Network, ISON) に因む。
発見時は視等級が19等級程度の極めて暗い天体として発見されたが、地球から約10億km程度離れた木星周回軌道付近にある点を考慮すると、既に非常に明るい彗星。
アイソン彗星は、近日点距離が187万km (0.0125AU) しかない、極めて太陽に接近するサングレーザー。
これは太陽の表面からたった117万kmである。このため、2013年の11月からは肉眼で見える明るさとなり、近日点通過前後の11月28日には、視等級がマイナスになり、金星や満月の明るさを超える大彗星になる可能性もある(視直径は満月より小さい)。

また、史上最も明るくなった1680年の大彗星と呼ばれるキルヒ彗星 (C/1680 V1) と軌道が似ており、これに匹敵するか超える明るさとなる可能性もある。
ちなみに日本では近日点通過時は地平線の下であり見ることはできない。
また、核の大きさは4.8kmと推定されている。

なお、彗星の明るさの予測は非常に難しく、核の直径・近日点距離・地球からの距離という要素が揃っているアイソン彗星であっても、1973年のコホーテク彗星のように、予測の通りに明るくならない可能性もある。

Comet ISON (アイソン彗星) : Picture

Comet ISON
Comet ISON
(C) ESO
This new view of Comet C/2012 S1 (ISON) was taken with the TRAPPIST national telescope at ESO's La Silla Observatory on the morning of Friday 15 November 2013. Comet ISON was first spotted in our skies in September 2012, and will make its closest approach to the Sun in late November 2013.

TRAPPIST has been monitoring comet ISON since mid-October, using broad-band filters like those used in this image. It has also been using special narrow-band filters which isolate the emission of various gases, allowing astronomers to count how many molecules of each type are released by the comet.

Comet ISON was fairly quiet until 1 November 2013, when a first outburst doubled the amount of gas emitted by the comet. On 13 November, just before this image was taken, a second giant outburst shook the comet, increasing its activity by a factor of ten. It is now bright enough to be seen with a good pair of binoculars from a dark site, in the morning skies towards the East. Over the past couple of nights, the comet has stabilised at its new level of activity.

These outbursts were caused by the intense heat of the Sun reaching ice in the tiny nucleus of the comet as it zooms toward the Sun, causing the ice to sublimate and throwing large amounts of dust and gas into space. By the time ISON makes its closest approach to the Sun on 28 November (at only 1.2 million kilometres from its surface — just a little less than the diameter of the Sun!), the heat will cause even more ice to sublimate. However, it could also break the whole nucleus down into small fragments, which would completely evaporate by the time the comet moves away from the Sun's intense heat. If ISON survives its passage near the Sun, it could then become spectacularly bright in the morning sky.

The image is a composite of four different 30-second exposures through blue, green, red, and near-infrared filters. As the comet moved in front of the background stars, these appear as multiple coloured dots.

TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) is devoted to the study of planetary systems through two approaches: the detection and characterisation of planets located outside the Solar System (exoplanets), and the study of comets orbiting around the Sun. The 60-cm national telescope is operated from a control room in Liège, Belgium, 12 000 km away.

Comet ISON
Comet ISON Passes Through Virgo
(C) NASA/MSFC/Aaron Kingery
Comet ISON shines in this five-minute exposure taken at NASA's Marshall Space Flight Center on Nov. 8 at 5:40 a.m. EST. The image has a field of view of roughly 1.5 degrees by 1 degree and was captured using a color CCD camera attached to a 14" telescope located at Marshall. At the time of this picture, Comet ISON was 97 million miles from Earth, heading toward a close encounter with the sun on Nov. 28. Located in the constellation of Virgo, it is now visible in a good pair of binoculars.

Comet ISON
Comet ISON Enhanced
(C) NASA/MSFC/MEO/Cameron McCarty
Taken on Nov. 19, 2013, this image shows a composite "stacked" image of comet ISON. These five stacked images of 10 seconds each were taken with the 20" Marshall Space Flight Center telescope in New Mexico. This technique allows the comet's sweeping tail to emerge with more detail.

Bright Comet ISON
Bright Comet ISON
(C) NASA/MSFC/MEO/Cameron McCarty
Comet ISON shines brightly in this image taken on the morning of Nov. 19, 2013. This is a 10-second exposure taken with the Marshall Space Flight Center 20" telescope in New Mexico. The camera there is black and white, but the smaller field of view allows for a better "zoom in" on the comet's coma, which is essentially the head of the comet.

Active Comet ISON
Active Comet ISON
(C) Babak Tafreshi (TWAN)
Falling through planet Earth's predawn skies toward its close encounter with the Sun on November 28, Comet ISON is coming to life. The much anticipated comet has now been reported to have substantially increased in activity, surging to naked-eye visibility for dark sites and sprouting a more complex tail. ISON's tail stretches over two degrees in this telephoto skyview from southern Kenya, captured on the morning of November 14. Shown in two panels, the enlarged negative version on the right makes details of the long tail easier to trace, including the tail's separated filaments toward the top of the frame. A sungrazer and first time visitor to the inner solar system, the possibility of ISON's survival to become a bright comet in planet Earth's December skies remains a question.

Comet ISON Before and After
Comet ISON Before and After
(C) NASA, SOHO
Sungrazing Comet ISON reached perihelion, its closest approach to the Sun, yesterday, November 28, at 18:45 UT. The comet passed just over 1 million kilometers above the solar surface, a distance less than the diameter of the Sun. These two panels follow ISON before (right) and after its close approach, imaged by the LASCO instrument onboard the Sun staring SOHO spacecraft. Overwhelming sunlight is blocked by LASCO's central occulting disk with a white circle indicating the Sun's positon and scale. The bright comet is seen along its path at the bottom of the before panel, but something much fainter exits near the top of the after panel, potentially a dust tail reforming from the debris left from ISON's perihelion passage.

Comet ISON
Comet ISON
(C) ESA/NASA/SOHO/GSFC
ISON appears as a white smear heading up and away from the sun. ISON was not visible during its closest approach to the sun, so many scientists thought it had disintegrated, but images like this one from the ESA/NASA Solar and Heliospheric Observatory suggest that a small nucleus may be intact

Comet ISON Comet ISON
Comet ISON
(C) ESO
Comet ISON
(C) NASA
Comet ISON Comet ISON
Comet ISON
(C) NASA
Comet ISON
(C) NASA
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Comet ISON (アイソン彗星) : Movie

NASA | Comet ISON's Path Through the Solar System

NASA | Comet ISON's Full Perihelion Pass
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「ウィキペディア(wikipedia):フリー百科事典」より文章引用。
アイソン彗星. (2013, November 30). In Wikipedia.
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